Tsetse challenge, trypanosome and helminth...
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Tsetse challenge, trypanosome and helminth prevalences, and productivity of village
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Ndama cattle in Senegal
3
A. Fa11’,2 , A. Diack’, A. Diaité3, M. Seye3 and G.D.M. d’Ieteren4
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‘Institut Sénégalais de Recherches Agricoles, CRZI Kolda , BP 52, Kolda, Senegal.
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2Centre for Tropical Veterinary Medicine. Easter Bush Roslin, Midlothian, EH25 9RG, Scotland
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31nstitut Sénégalais de Recherches Agricoles, LNE;RV, BP 2057, Dakar, Senegal
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41ntemational
Livestock Research Institute, P.O. Box 30 709, Nairobi, Kenya
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Ahstract
9
Data on tsetse fly, and on village Ndama cattle collected over a 4-year period in southem Senegal, were analysed.
10
A total of 531 Ndama came in 4 herds of 3 villages in the Kolda area were monitored monthly. Glossina
11
morsitans submorsitans and Glossina nalnalis nambiensis are present in the study area. Mean tsetse apparent
12
density was 5.4 flies/trap/day.
Trypanosome (Trypanosoma conyonlense
and Trvuanosoma vivax) infection rate
13
in flies was 2.5(s.e. 0.37)%. Tsetse challenge index was 17.3(s.e. 4.18). Mean monthly trypanosome prevalence
14
in came was 2.5(s.e. 0.51)%. Highest trypanosome prevalence occurred during the dry season, and animals less
15
than 1 year old were more frequently infected than older animals. The linear relationship between the loglO+l
16
tsetse challenge and the arcsine of the trypanosome prevalence was significant only when mean monthly values
17
of these variables over the 4-year period were used with tsetse challenge preceding infection rate by 3 months.
18
Mean monthly prevalence of strongyle, strongyloides, ascaridia and coccidia were 34.4(s.e. 0.60), 2.l(s.e. 0.18),
19
1.2(s.e. 0.45) and 15.6(s.e. 0.47)%, respectively. Calf mortality rate at 1, 6 and 12 months of age was 2.l(s.e.
20
2.1), 5.2(s.e. 2.8) and 12.2(s.e. 3.3)%, respectively. Calving interval (584 s.e. 58 days) was not influenced
by
21
trypanosome status of the cow during lactation. Calving interval was shorter by 167 days when the calf died
22
before one year of age in comparison
to calving intervals for which the calf survived beyond one year. Live
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weight at birth, 6 and 12 months of age were 15.8(s.e. 0.54), 48.X(s.e. 2.56) and 71.l(s.e. 5.44) kg, respectively.
24
Mean lactation length, total and daily milk offtake were 389(s.e. 16) days, 231(s.e. 15) litres and 0.69(s.e. 0.037)
25
litres, respectively. Trypanosome infection during lactation did have a significant effect on the amount of milk
26
extracted for human consumption
nor did trypanosome status affect calf growth.
27
Key words: Ndama came, tsetse challenge, trypanosomiasis,
helminthiasis, productivity, Senegal.
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Introduction
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Because of their trypanotolerance, Ndama cattle constitute a unique animal genetic resource
31
which forms the basis of large ruminant agriculture in many parts of West Africa where the
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risk of trypanosomiasis is high. The Ndama cattle breed are a multipurpose breed that produce
33
milk, meat, power and manure and therefore contribute a great deal to the income and welfare
34
of millions of farmers in mixed trop-livestock production systems in West Afiica. However a
35
complex set of technical factors related to health, nutrition and management constrain the
36
productivity of Ndama cattle kept under traditional husbandry systems. The relative
37
importance of these factors needs to be determined i.f strategies to make better use of this
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genetic resource are to be developed to meet the growing demand for animal products in West
39
Africa. TO this end, an epidemiological study was carried out from 1988 to 1992 in the
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Casamance region of southem Senegal to investigate causes of variation of Ndama cattle
41
productivity and the stability of the trypanotolerance trait under village management systems.
42
This study was part of a large epidemiological programme that was conducted by International
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Livestock Centre for Africa (ILCA now ILRI) and National Agricultural Research Institutes in
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many sites in Africa with different degrees of trypanosomiasis risk. This paper reports fïndings
45
on the tsetse challenge, prevalence of parasitic diseases (helminthisiasis, trypanosomiasis) in
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village Ndama cattle in southern Senegal and
how these factors affect reproduction
47
performance, calf growth and milk production.
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49
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51
52
53
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Correspondance address: Dr Abdou FAL(L Institut Senegalais de Recherches Agricoles, Laboratoire National
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d’Elevage et de Recherches Vétérinaires, BP 2057, Dakar, Senegal, Tel (221) 832 3678, Fax (221) 832 2118
1
Materials and Methods
2
The study area
3
The study was carried out in the region of Casamance in Southem Senegal. The climate in this
4
region is of a sudano-guinean type and annual rainfall during this study at Kolda was 1018,
5
1045, 787, and 684 mm in 1988, 1989, 1990 and 1991., respectively. The unimodal rainfall at
6
Kolda occurs between June and October. Four herds in three villages (Salamata, Yassiriba,
7
Sare Pathe) were selected for the evaluation of Ndama cattle health characteristics and the
8
estimation of production parameters. Salamata and Yassiriba are along the Mahon forest
9
boundaries and close to a stream. Sare Pathe is located in the forest of Bakor.
1 0
11
Herd management
1 2
Multipurpose Ndama cattle are kept in the mixed trop-livestock farming system at Kolda as a
1 3
supplier of food (milk), cash through offiake for meat, power for cropping and transport, and
1 4
for manure for the restoration of soi1 fertility. Animals belonging to many individuals form a
1 5
herd which is under the responsibility of the head of a household. Animals graze natural
1 6
pastures which form the main source of the food supply. Pastures are abundant and are of good
1 7
quality during the rainy season and early dry season. After the grain harvest, animals have
1 8
access to upland (millet, sorghum) and lowland (rice) trop residues that are consumed directly
1 9
in the fields. Shortage of food supply during the critical months of March, April, May and
20
June is the single most important constraint that face herd owners in this area.
2 1
22
Animals are tethered individually ovemight in a trop fïelds during the dry season and are
23
moved to the forest during the cropping season to avoid damage to crops. Mating is not
24
controlled and calving occurs a11 year round. However peak calving is recorded in July and
25
August. Milking is performed once a day, and begins one week afier calving. The calf is
26
allowed to suckle its dam for a few seconds to trigger milk let-down and thereafter, is tethered
27
at the foot of the dam during the course of milking. The residual milk is suckled by the calf.
28
Suckling of calves takes places a second time in the evening when adult animals retum from
29
grazing. Calves are tethered over night to prevent suckling. They also graze separately from
30
adults in areas surrounding homesteads. A main feature of the milking system in the Kolda
31
area is that milking for human consumption is suspended during part of the dry season and is
32
resumed during the next wet season.
33
Experimen ta1 design
34
This study was carried out over a 4-year period (1988 to 1992). Data was collected
35
concomitantly on tsetse challenge, animal health and animal production parameters.
36
37
Animais
38
A total of 531 Ndama cattle kept in 4 herds of 3 villages were monitored monthly for 52
39
months in Salamata and Yassiriba with 163 animals, and for 24 months in Sare Pathe with 268
40
animals. Animals were individually tagged on both ears. At the start of the programme each
41
anima& age and the number of calving of each adult female were estimated by farmers.
42
Animals were managed under traditional village conditions and therefore were subjected to
43
natural tsetse challenge. Routine vaccination against rinderpest, anthrax, hemorrhagic
44
septicaemia, and contagious bovine pleuropneumonia was given. Animals were also treated
45
with diminazene aceturate (Berenil, 3.5 mg kg-’ body weight) when trypanosomes
were
46
detected and the packed red ce11 volume (PCV) was below 20%.
47
48
Field recording and laboratory determinations
49
Monitoring of tsetse flies
50
Twelve biconical traps, as described by Challier and Laveissière (1973), were placed at each
5 1
site each month for 3 consecutive days and harvested every 24 hours. Traps were set 100 m
2
apart from each other. Furthermore they were distributed in Savannah and river-me areas within
2
the forests of Bakor and Mahon which constitute common grazing areas for cattle from
3
surrounding villages. Al1 flies caught were identified and recorded with reference to biotope,
4
species, sex, teneral/non-teneral status, and age group by wing-fi-ay method as described by
5
Jackson(l946). Al1 live non-teneral flies were then dissected in a 0.9% saline solution and the
6
midgut, labrum, hypopharynx and the salivary glands were examined for the presence of
7
trypanosomes by phase-contrast microscopy at 320x magnification using a combination of
8
Periplan 10x eyepieces and a long-distance L32 objective.
9
10
Cattle herd monitoring
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Each month, immediately following the tsetse trapping on the site, blood samples were
1 2
collected from the jugular vein of the cattle into evacuated tubes containing EDTA. The PCV
1 3
was measured and the level of parasitaemia estimated -using phase-contrast examination of the
1 4
blood buffl-coat (Murray et al., 1983). Whenever the PVC declined below 20%, blood smears
1 5
were made in order to determine if other hemoparasites (e.g., babesia spp, anaplasma spp.)
16
were present. Faeces samples were collected from the animal’s rectum for the entire herd every
1 7
3 months and monthly for animals aged O-3 years. Faecal samples were immediately examined
1 8
for the presence of gastro-intestinal parasites using the McMaster Egg-counting technique
1 9
(Murray et al., 1983). Animals were weighed each month using an electronic scale (Barlo,
20
Australia) and milk offtake for human consumption was measured using a graduated tube.
2 1
Information on herd dynamics including date of birth, mortality and animal transactions (e.g.,
22
purchases, sales, exchanges and transfers) were routinely collected during weekly herd visits.
23
24
Data analysis
25
Data was analysed using SAS General Linear Mode1 procedures (SAS, 1989). A regression
26
analysis of the arcsine of trypanosome prevalence on L,oglO+l of the challenge index (CI), the
27
product of the apparent density and the infection rate of flies, was performed to investigate the
28
relationship between these two variables. Village and herd within village, month and year the
29
observation was made, age category (category 1: < 1 year, category 2: 1 to 3 years, category 3:
30
>3 years) and sex of the animal (female, entire male, castrated male) were included in a11
3 1
analyses of health parameters and production traits. Specific additional factors were also
32
included as necessary. Additional sources of variation for the analysis of trypanosome
33
prevalence included the level of infection with strongyle parasites ( level 1: 0 egg per gram of
34
faeces (epg), leve12: 100-500 epg, leve13: > 500 epg).
35
36
The analysis of PCV included the trypanosomiasis status of the animal and the interaction
37
between trypanosome and helminthiasis infections. The data set used to investigate the effects
38
of these factors on PCV was formed by using data from animals for which both faecal and
39
blood samples were taken and analysed for the determination of blood and gastro-intestinal
40
parasites. Also, the data set used to analyse PCV excluded data from 49 animals which were
41
infected with babesia or anaplasma. These animals ha.d a mean PCV of 19 (S.D. 10) %. This
42
was intended to exclude the influence of these diseases on the evolution of anaemia and
43
therefore to improve estimates of PCV based on factors included in the statistical model.
44
45
For the analysis of calving interval, the effects of parity of the previous parturition and the
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trypanosome status of the cow were investigated. Calving number was classified into two
47
groups, with group 1 formed by parturition number 1 and 2, and group 2 composed of cows
48
with 3 or more calvings. Cows were also grouped into non-infected and infected with
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trypanosomes after the fïrst parturition of the inter-val. Trypanosome status was also included
50
in the analysis of calves live weight (LW) growth up to the age of 12 months. Two classes of
3
infection status (non-infected and infected at least once with trypanosomes), between the age
2
of 0 to 6 months and between 6 to 12 months, were formed.
3
4
For the analysis of lactation length, total and daily milk for human consumption, the following
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classes of factors were included: 3 seasons of calving (season 1, the wet season: June, July,
6
August, September with minimum and maximum ambient temperatures of 24 and 34 “C,
7
season 2: the cool dry season, October, November, December with minimum and maximum
8
ambient temperatures of 18 and 35 “C and season 3, the hot dry season, February, March,
9
April, May, with minimum and maximum ambient temperatures of 21 and 39 “C), 2 levels of
10
infection status (non-infected and infected at least once during lactation irrespective of the
11
time during lactation when infection occurred), the interaction between season and infection
12
status, and 2 types of milk extraction practices (continuous milk extraction throughout
13
lactation, and suspension, and later resumption of milk offtake).
14
15
Mean calving intervals and cow survival rate, calf mortality rate, calf live weight at one year,
16
and milk offiake for human consumption, were combined to determine productivity indices as
17
described by Agyemang et al. (1991).
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19
Results
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Tsetse challenge
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Tsetse flies present in the study area were identified as G. m. submorsitans and G. n.
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gambiensis. Out of the 10,210 flies caught from Marc11 1988 to March 1992, 64% were G. m.
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submorsitans and 36% were G. D. gambiensis. The number of flies caught per trap per day is
24
an estimate of the apparent density of tsetse flies and the average apparent density found in
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this study was 5.4 flies/trap/day. Although the apparent density was highest between January
26
and April with a peak in February the two tsetse species showed different patterns of
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distribution over the year. The number of G. p. Gambiensis trapped was highest during the
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rainy season (June to September) and during the first months of the dry season (November,
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December, January) whereas most of catches of G. m. submorsitans occurred during the
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second half of the dry season (February and May). Finally, there were more marked seasonal
31
changes in the distribution of G. m. submorsitans than in that for G. D. aambiensis.
32
33
The dissection of 50% of caught flies gave a mean monthly infection rate by T. congolense a
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T. vivax of 2.4 (s.e. 0.37)% during the 4-year period of the monitoring programme. Mean
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monthly CI, an estimate of the trypanosomiasis risk, was 17.3 (s.e. 4.18). Figure 1 shows the
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seasonal pattern of changes in CI. Tsetse challenge was more pronounced hem January to
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April, peaked in March and decreased gradually as the dry season progressed. Lowest CIs
38
were recorded during the rainy season. There was a Sharp decrease in tsetse apparent density in
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1991 and 1992 compared to 1988 and 1990.
40
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Trypanosomiasis infection rates in Ndama cattle
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The overall mean trypanosome prevalence was 2.5(s.e. 0.51)%. Infection rates due to T,
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congolense and T. vivax were 1.89(s.e. 0.43) and 0.64(:s.e. 0.27)%, respectively. Trypanosome
44
infection rates were signifïcantly affected by village (Pc O.OOl), month of the year (P<O.Ol)
45
and age of the animal (P<O.OOl). The monthly relative number of animals infected with
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trypanosomes was larger in Yassiriba (4.3 s.e. 0.68 %) than in Salamata (1.5 s.e. 0.54 %) or
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Sare Pathe (1.7 s.e. 0.59%). Figure 3 shows seasonal variation in trypanosome prevalence.
48
Trypanosome infection rates increased steadily each year fiom January, during the dry season,
49
and peaked in June, the end of the dry season. A gradua1 decrease of the infection rates was
50
then observed from June, during the rainy season. Lowest infection rates were recorded in
51
December and January.
4
Figure 3 shows that there was a time lag of 3 months between peak of the trypanosome
2
prevalence and that of the tsetse challenge. When the log+l of the monthly tsetse challenge
3
was regressed on the arcsine of the mean monthly infection rates aggregated over the 4-year
4
period, significant relationship (R2 = 0.52, PcO.01) was detected between these two factors.
5
However this relationship was no longer significant when the 48 monthly infection rates and
6
monthly tsetse challenges were used in the regression analysis.
7
8
Adult animals aged more than 3 years were more affected by trypanosomes (3.6 s.e. 0.5 %)
9
than younger animals (1.9 s.e. 0.5 %).
Although the effect of strongyle infection on
1 0
trypanosome infection rates was not signifïcant (PI> 0.05), animals which were heavily
11
infected with strongyle tended to be more infected with trypanosomes (epg > 500 epg,
1 2
trypanosome infection rate = 3.8 s.e. 1.01 %) than those with medium infestation (epg = lOO-
1 3
500 epg, trypanosome infection rate = 2.5 s.e. 0.69 %) or those which were strongyle free
1 4
(trypanosome infection rate = 2.6 s.e. 0.62 %,). Castrated males tended also to be less infected
1 5
with trypanosomes than both entire males and females (Table 2) but the difference was not
16
significant (P= 0.16).
1 7
1 8
Gastro-intestinal parasites
1 9
The analysis of 6,016 animal-month faecal samples gave a mean monthly prevalence of 34.4
20
(s.e. 0.60), 2.1 (s.e. 0.18), 1.2(s.e. 0.45) and 15.6(s.e. 0.47)Oh for strongyle, strongyloides,
2 1
ascaridia and coccidia types of infestation, respectively.
22
23
Figure 2 shows seasonal variations of strongyle infection and worm burden. Strongyle
24
prevalence and egg output were lowest during the dry months of January to May. The number
25
of animals infested with strongylidae increased gradually each year from April to reach a peak
26
in June and remained high (>40%) in July, August and September, the wettest months of the
27
year. The worm burden followed the same pattern, but its peak occurred in September, 3
28
months later than the peak of strongyle prevalence.
29
30
Mean strongyle egg counts were higher in animals less than 1 year old (epg = 346 se. 47)
31
than in animals l-3 years old (epg = 286 s.e. 43), or in animals more than 3 years old (epg =
32
220 se. 44). For animals carrying strongyle-type parasites, worm burden tended to be heavier
33
in those infected (epg = 318 s.e. 75) in comparison to those not infected with trypanosomes
34
(epg = 250 s.e. 20), but the difference was not significant. It has also been noted that
35
strongyloides prevalence was higher in animals infected (4.4 se 0.35%) than in animals not
36
infected (1.9 s.e. 0.35%) with trypanosomes. Age had a significant effect on prevalence of
37
ascaridia and strongyloidae. Young animals less than 1 year old were more frequently infected
38
with than older animals. Ascaridia were rare in animals between 1 and 3 years old and were
39
absent in animals more than 3 years old. The prevalence of strongyloides was also lower in
40
animals more the 1 year old (1.8 s.e. 0.74%) than in animals less than 1 year old (5.8 s.e. 0.80
4 1
%). Although adult animals were free of ascaridia and strongyloides, the prevalence of
42
strongyle-type infestation was almost as high (34 s.e. 2.5%) as in Young animals (36 s.e. 2.7).
43
44
Packed ce11 volume
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Packed ce11 volume, which is an indication of the degrele of anaemia, was significantly affected
46
by the year (PcO.01) and month (PcO.01) during which PCV was determined, sex (PcO.01)
47
and age (PcO.01) of the animal, and trypanosome infection (PcO.01). In general there was
48
trend of a decline of PCV from 1988 to 1992 (Table 2). Each year, PCV reached its peak in
49
February and the lowest values were recorded from May to October, coinciding with the end
50
of the dry season and the rainy season (Figure 3). Highest PCVs were recorded each year fi-om
5 1
November to February, with peak values reached in February. Thereafter, there was a Sharp
5
decrease of PCV values from February to May. This period coincided with the time when food
supply was critical and when significant increases in trypanosome infection rates were seen.
In general there was a decline in PCV values of 3.3 % in animals infected with trypanosomes
as compared to those not infected. Castrated males had higher PCV than entire males or
females. The effect of strongyle infection was close to signifïcance levels (P=O.O8). In general
strongyle-free animals had higher PCV than infected animals. Although the effect of the
8
interaction between strongyle and trypanosome infections was not signifïcant, PCV values
9
shown in table 2 suggest an additive effect of these infections on the development of anaemia.
1 0
11
Production parameters
1 2
Mortality rates
1 3
Out of the 225 calves bom during the course of the monitor-mg programme, 2.1 (se. 2.1), 5.2
1 4
(s.e. 2.8) and 12.2 ( s.e. 3.3%) died before the age of 1, 6 and 12 months, respectively. The
1 5
effect of herd on mortality rates at 1 and 6 months of age was signifïcant (PcO.05). Sex of the
1 6
animal, year and month of birth and parity did not signifïcantly influence mortality rates.
1 7
1 8
Calving in tervals
1 9
Sixty eight calving inter-vals of cows that gave birth in 1988, 1989 and 1990 were analysed.
20
The unadjusted mean calving interval was 634 (S.D. 186) days. The least square mean calving
2 1
interval was 584 (s.e. 58) days. Year and parity of previous parturition and calf survival to 1
22
year had significant effects (PcO.05) on calving inter-val. Cows whose calf died before the age
23
of 12 months had calving intervals shorter (by 167 days) than that of cows whose offspring
24
survived beyond 12 months of age.
25
26
The trypanosomiasis status of cows did not affect significantly calving inter-vals. When the
27
previous calving number was 1 or 2, the calving interval was greater by 98 days than when
28
previous calving number was greater or equal to 3. Mean calving inter-vals were 663 (s.e. 78),
29
493(s .e. 73) and 445(s.e. 65) days for cows that calved previously in 1988, 1989 and 1990,
30
respectively.
31
32
33
Live weight changes
34
Live weight at birth, 6 and 12 months of age were 15.8 (s.e. 0.54), 48.l(s.e.2.56) and 71.lts.e.
35
5.44) kg, respectively. Only the season of calving had a significant effect on calf weight at 6
36
months of age. Calves bom during the late dry season (February to May) were lighter (PcO.05,
37
42.9 s.e. 3.48 kg) than those bom during the wet season (50.5 s.e. 2.95 kg) or in the early dry
38
season (50.7 s.e. 3.09 kg). Trypanosome infection status did influence significantly calf live
39
weight at 6 or 12 months of age.
40
4 1
The average LW of empty cows was 222(s.e. 1.3) kg. However there was marked seasonal
42
fluctuation of cow LW during the year. Cows lost LW during the second half of the dry
43
season, from March to June and they gained LW progressively during the wet season, but it
44
was until November, the early dry season, that they fùlly recovered their LW. The magnitude
45
of LW losses between the highest LW in November and the lowest LW in June was an
46
average of 25 kg.
47
48
Lactation characteristics
49
Milk extraction was suspended during the dry season in 42% of lactating cows that were
50
subjected to milk recording. The average number of days milking was suspended was 127 days
5 1
with a minimum of 52 and a maximum of 298 days.
6
1
2
Mean lactation length, total milk extracted for human consumption and daily milk offtake
3
were 389(s.e. 16) days, 231(s.e. 15) litres and 0.69(s.e. 0.037) litres, respectively. However
4
season of calving had a significant effect (PcO.01) on lactation length. Lactation length was
5
longer when calving occurred during the wet season (season 1: June to September: 446 s.e. 18
6
days) than when calving took place during the early dry season (season 2: October to January:
7
358 s.e. 23 days) or during the late dry season (season 3: February to May: 365 s.e. 33 days).
8
Cows for which milk offtake was suspended had a longer lactation length (452 s.e. 18) days)
9
than cows that were continuously milked (327 s.e. 20 days). Total milk extracted for human
1 0
consumption was affected by calving season and herd. Cows that calved in season 1, the wet
1 1
season, out-produced (264 se. 17 litres) cows that gave birth during the dry season (seasons 2
1 2
and 3). Cows starting lactation in season 2 and 3 produced 188 (s.e. 22) and 240 (s.e. 31)
1 3
litres, respectively.
1 4
1 5
The interaction between season of calving and trypanosome infection on lactation length was
1 6
significant (PcO.05).
Cows that gave birth between February and May and that were infected
1 7
with trypanosomes during lactation had the shortest lactation length of 318 (s.e. 60) days.
1 8
Trypanosome infection did not appear to affect lactation length when calving occurred in the
1 9
wet season or in the early dry season. Total and daily milk offtake appeared also to be minimal
20
in cows that calved between February and May and that were infected with trypanosomes
2 1
during lactation, but these differences were not significant. When calving occurred between
22
October and January and the cows were detected parasitaemic, total and daily milk offtake
2 3
were 166(s.e. 36) and 0.560(s.e. 0.09) litres, respectively. In contrast cows that calved in the
24
same period but that were not detected parasitaemic produced 210(s.e. 18) litres during the
2 5
entire lactation and 0.740 (s.e. 0.044) litres per day. Trypanosome infections that occurred
26
during the wet season or during the last part of the dry season did not seem to affect milk
2 7
offtake. Total milk offtake of non-infected and infected cows that started lactation between
2 8
February to June were 242(s.e. 23) and 238(s.e. 56) litres, respectively.
29
30
Productivity indices
3 1
Mean calving inter-val (584 days), cow survival rate ( 98.5% per year), calf survival rate (88 %
32
per year), calf LW at one year of age (71 .l kg), and milk offtake during the first 12 months of
3 3
lactation (216 kg) found in this study were combined t:o produce productivity indices. Index 1
34
which is the amount of one-year old calf LW plus the LW equivalent of milk extracted for
3 5
human consumption produced per cow per year was 62.8 kg. Index 2, the LW of one-year old
36
calf produced plus LW equivalent of milk offtake per 100 kg of cow maintained per year was
3 7
28.8 kg. Index 3, the LW of a one-year old calf produced plus LW equivalent of milk offtake
3 8
per 100 kg of cow metabolic LW was 120.8 kg.
39
40
Discussion
4 1
In the present study, the population of tsetse flies decreased over the experimental period. The
42
apparent density of tsetse flies was particularly low in 1991 and 1992 as compared to previous
4 3
years. These changes in the population of flies may be attributed to the effect of continuous
44
trapping for 4 years in the same site. Another contributing factor to the decline of the tsetse
4.5
population could have been the reduced rainfall recorded during 1991 and 1992 and also the
46
occurrence of bush-fïres which may have destroyed fly habitat or caused migration of the fly
47
population. However, the decline in the challenge index in 1991 and 1992 did not translate
48
into reduced trypanosome infection rates in cattle during these years. The regression of the
49
monthly trypanosome infection rates on the monthly challenge index after a log transformation
5 0
of tsetse challenge and arcsine transformation of trypanosome infection rates showed a
51
significant correlation between these two parameters. However, cor-relation was only apparent
when data was aggregated over the 4-year period and that challenge preceded the prevalence
2
data by three months. The correlation of these two parameters on a monthly basis year by year
3
failed to detect any Sign&ant relationship betwee:n these two factors. The absence of
4
signifïcance relationship was even apparent when the moving average of the tsetse challenge
5
was used in the regressions analysis. There were many months when the number of flies
6
caught was zero in 1991 and 1992, but trypanosomes were detected in the blood of the
7
animals. This suggests that although the challenge index in a simple field estimate the
8
seriousness of trypanosomiasis in an area, it may fail to give valid assessment of the problem
9
if data is collected for a short period of time or if there are many months when the challenge
1 0
index is zero. Even when the index is zero it does not mean that flies are totally absent.
1 1
Vectors other than G. m. submorsitans and G. p. gambiensis may also have played a role in
1 2
the transmission of trypanosomes to cattle.
1 3
1 4
Mean trypanosome prevalence (2.5%) found in the present study is relatively low. Animals in
1 5
Yassiriba were more frequently infected with trypanosomes than those in Yassiriba and Sare
1 6
Pathe. The herd size in Yassiriba was smaller than in other villages. This, coupled with the fact
1 7
that Yassiriba was located deeper in the forest and at the vicinity of a stream may have created
1 8
conditions for animals in Yassiriba to be more exposed to tsetse flies than in other villages
1 9
where these conditions did not occur.
20
2 1
In the present study there was an increase in the trypanosome prevalence as animals aged. The
2 2
higher capacity of Young animais to resist trypanosomiasis relative to adult animals has
2 3
already been reported (Stephen, 1986; Rowlands et al., 1993) and is suggested to be related to
24
the superior erythropoeitic response of younger animals (Murray, 1988). However as
2 5
suggested by Rowlands et al. (1993), differences in exposure may contribute to these variation
26
in trypanosome prevalence in animals of different age classes. In this study castrated males
2 7
were also less subjected to trypanosome infection than entire males and females. It would have
2 8
been thought that being used for work, the physical stress castrated males undergo during work
29
would increase their susceptibility to infection. It is likely that both Young animals and
30
castrated males are less infected than other categories of animals because of differences in
3 1
their respective management. Not only are draught animals better fed during the dry season but
3 2
also both Young animals and draught animals graze at the vicinity of homesteads and are not
3 3
watered in gallery forest where contact with flies is more likely.
3 4
3 5
The time lag between peaks of tsetse challenge and trypanosome prevalence in cattle found in
36
this study is similar to that reported in studies in Ethiopia (Rowlands et al., 1993) and the
3 7
Gambia (Claxton, 1992). This is supposedly due to the time interval between the infective bite
3 8
and the detection of trypanosomes in the animals (Leak et al, 1993).
3 9
40
In this study, heavy strongyle burden was conducive to increased trypanosomiasis
4 1
susceptibility. The same finding is reported in Ndama cattle in the Gambia (Dwinger et al.,
42
1994).
4 3
44
Although this study showed a significant relationship between trypanosome prevalence and
4 5
tsetse challenge, the seasonal variations of trypanosome infection rates suggests also that
46
nutrition could be a confounding factor. Indeed, increases in trypanosome prevalence during
47
the dry season, from January to June, coincided with poor nutrition during that period and the
48
consequent reduction in animal LW and PCV%. Work done in the Gambia showed that
49
nutritional stress depresses the capacity of the animals to tope with trypanosome infections
5 0
(Little et al., 1994).
5 1
8
B<
’
.
1
The present study has also provided information on the epidemiology of helminthiasis in
2
Ndama cattle in southern Senegal. Infestations with strongyle-type parasites were more
3
fi-equent and the worm burden was heavier in the wet season than in the dry season. In general
4
adult animals appeared as frequently infested with strongyle parasites as younger animals and
5
therefore constitute a source of contamination of pastures. Studies in the Gambia revealed the
6
same epidemiological characteristics of gastrointestinal nematodes in Ndama cattle (Kaufmann
7
and Pfïster, 1990). It has also been demonstrated in the Gambia (Kaufmann and Pfister, 1990)
8
that Heamoncus contortus is the most frequent strongyle, which cari cause severe anaemia,
9
pastures are f?ee of infective larvae during the dry season and third, pasture recontamination in
1 0
the early wet season is caused by the development of inhibited Heamoncus larvae and residual
1 1
adult worms. Results from the present study suggest also that an interaction exists between
1 2
trypanosome and helminthiasis infections. Trypanosomiasis was more frequent in animals
1 3
heavily infested with strongyle parasites. The decline in PCV in animals infested with
1 4
strongyles seen in this study suggests that strongyle infestation may depress the capacity of
1 5
Ndama cattle to withstand trypanosome infections. Such an influence of helminth infections
1 6
on the susceptibility to trypanosomiasis is reported in the Gambia (Dwinger et al., 1994).
1 7
1 8
Additionna1 work in this study has also shown that when calving occurred during the late dry
1 9
season calves had a slow growth rate up to 6 months of age. Growth of calves born during this
20
period was impaired by low milk output of the dam due to poor nutrition. Trypanosome
2 1
infection did not signifïcantly affect calf growth. This, coupled with the fact that higher PCV
2 2
seen in animals younger than 1 year as compared to older animals and therefore their better
2 3
ability to resist anaemia, give further evidence of the capacity of Young animals to be more
24
resistant to trypanosomiasis than adult animals.
2 5
2 6
Although previous studies (Agyemang et al., 1993) bave indicated the depressing effect of
2 7
trypanosome infection on reproductive performance, in the present study calving interval was
2 8
not affected by the trypanosome status of Ndama cows during lactation. This finding is in
29
agreement that of Thorpe et al. (1988). The most important factor that influenced the
3 0
reproductive performance in the work described here was whether the calf survived or not up
3 1
to 12 months of age. The calving inter-val of cows whose calf died before the age of 12 months
32
was lower by 167 days than that of cows that suckle their offspring over 12 months. Indeed,
3 3
the depressing effect of suckling on post-partum cyclicity of Ndama cows is reported by
34
Sanyang u.(1995). As pointed out by Thorpe et al. (1988), use of calving interval as an
3 5
estimate of reproductive performance fail to take into account non-fertile cows in the herd and
36
this may mask the effect of trypanosome infections on reproductive performance.
37
38
The mean lactation length (389 s.e. 16 days) and total milk for human consumption (231 s.e.
39
15 litres) found in this study carried out in southern Senegal where milking is done once a day
40
agree with the level of lactation performance by Ndama cows milked once daily in the
4 1
Gambia. Lactation length and milk offtake were 437(s.e. 16.6) days and 239(s.e. 19.3) litres in
42
the once-daily milking system in the Gambia (Agyemang, et al., 1991). Trypanosome
4 3
infection did not affect lactation length or total milk offtake. This again agrees with results
44
obtained in the Gambia where non-infected cows out-produced infected cows during lactation
4 5
by only 24 kg during a 14-month location period and this difference was not signifïcant
46
(Agyemang, et al., 1991). However trypanosome infection caused a reduction in milk
47
production during the 6 months following infection in Ndama cows in The Gambia
48
(Agyemang et al., 1990).
49
50
Larger lactation length and greater milk offtake seen in cows starting lactation during the wet
5 1
season when food was plentiful and of good quality as compared to the dry season, suggest
9
1
that nutrition is the driving factor that determines milk production of village Ndama CO~S.
2
Cows calving during the last part of the dry season performed better than those calving during
3
the early part of the dry season. For the latter, most of the lactation length occurred during dry
4
months whereas the former Will benefït fi-om the pastures improvement in the next wet season.
5
In terms of milk production, cows that gave birth between November and January were more
6
severely affected by food shortage than cows calving; in other seasons. Feed restriction was
7
compounded in these cows by trypanosome infections and led to the shortest lactation length.
8
The trends observed regarding the interaction of season of calving and trypanosome infection
9
on milk offtake suggest that well fed Ndama cows could produce milk with a no major
1 0
negative influence of trypanosome infection. Similarly, Agyemang et al. (1990) suggested that
1 1
the depressive effect of trypanosome infections on milk production could be reduced through
1 2
the provision of additional food to cattle showing signs of the disease.
1 3
1 4
Finally, the productivity indices found in this study (Index 1 = 62.8 kg per cow, Index 2 =
1 5
28.3 kg per 100 kg cow LW and index 3 = 120.8 kg per 100 kg metabolic LW) are in
1 6
agreement with productivity indices found in Ndama cattle under once-daily milking system in
1 7
The Gambia where index 1, 2 and 3 averaged 60.4, 28.3 and 120.2 kg (Agyemang et al.,
1 8
1991). Village Ndama cow productivity seems relatively lower than that found in Ndama cows
1 9
reared on station with no milk extraction. Productivity indices 1, 2 and 3 were 70.1, 29.1 and
20
127.0, respectively for Ndama cows reared on station in Senegal (Fall et al, 1983).
2 1
22
Acknowledgements
2 3
This work was jointly carried out by ISRA, ILCA and ILRAD and was supported by the
24
European Development Fund. Additional fund provided by the British Overseas Development
2 5
Administration (ODA) allowed the main author to spend time at the Centre for Tropical
26
Veterinary Medicine, University of Edinburgh to analyse and publish the data. Comments
2 7
fi-om A.S. Peregrine are greatly appreciated.
2 8
29
30
References
3 1
Agyemang, K., Dwinger, R.H. Grieve, A.S. and Bah, M.L., 1991. Milk production
3 2
characteristics and productivity of N’Dama cattle kept under village management in The
3 3
Gambia. Journal of Dairy Science, 74, 1559-1608
34
3 5
Agyemang, K., Dwinger, R.H. Jeannin, P., Leperre,P. Grieve,A.S. Bah, M.L. and Little, D.A.,
3 6
1990. Biological and economic impact of trypanosome infections on milk production in
37
Ndama cattle managed under village conditions in The Gambia. Animal Production, 50: 383-
38
389
39
40
Agyemang,K., Little, D.A. Mattioli, R., Sonko, E. and Janneh, L., 1993. Effects of
4 1
trypanosome infection and postpartum liveweight change on resumption of reproductive
42
activity in N’dama CO~S. Theriogenelogy, 39:985-995
4 3
44
Challier, A. et Laveissière, C., 1973. Un niveau piège pour la capture de glossines, description
4 5
et essais sur le terrain. Cah. Orstom Ser. Ent. med. Parasitol., no 11: 25 l-262
46
47
Claxton, J.R. Leperre, P., Rawlings, P., Snow:, W.F. and Dwinger, R.H., 1992.
48
Trypanosomiasis in the Gambia: Incidence, prevalence and tsetse challenge, Acta Tropica, 50,
49
219-225.
5 0
1 0
Dwinger, R.H., Agyemang, K., Kaufmann, J., Grieve, A.S. and Bah, M.L. 1994. Effects of
2
trypanosome and helminth infections on health and production parameters of village N’Dama
3
cattle in The Gambia. Veterinary Parasitology, 54,353-365
4
5
Fall, A., Diop, M., Sandford, J., Wissocq, Y.J. Durkin, J. and Trail, J.C.M., 1983.
6
Productivities of Djallonke Sheep and Ndama Cattle at the Centre de Recherches
7
Zootechniques at Kolda, Senegal. ILCA Research Report no. 3. ILCA, Addis Ababa,
8
Ethiopia.
9
10
Jackson, C.H.N., 1946. An artificially isolated generation of tsetse flies (Diptera). Bulletin of
11
Entomological Research, 37 :29 l-299
1 2
1 3
Kaufmann, J. and Pfister, K., 1990. The seasonal epidemiology of gastrointestinal nematodes
1 4
in N’Dama cattle in The Gambia. Veterinary Parasitology, 37,45-54
1 5
1 6
Leak, S.G.A., Woudyalew Mulatu, Authié, E., d’iteren, G.D.M., and Peregrine, A.S.,
1 7
Rowlands, G.J. and Trial, J.C.M., 1993. Epidemiology of bovine trypanosomiasis in the
1 8
Ghibe valley, Southwest Ethiopia. 1. Tsetse challenge and its relationship to trypanosome
1 9
prevalence in cattle. Acta Tropica, 53, 12 1- 134
20
21
Little, D.A., Wassinls, G-J., Agyemang, K., Leperre, P., Janneh, L. and Badje, B., 1994. Feed
22
supplementation of lactating N’Dama cows under village husbandry. Tropical Agriculture
23
(Trinidad), 71,223-228
24
25
Murray, M., 1988. Trypanotolerance, its criteria and genetic and environmental influences. In
26
Livestock Production in Tsetse Affected Areas of AfricA. Proceedings of a meeting held 23-27
27
November 1987, Nairobi, Kenya. International Livestock Centre for Afiica (ILCA)/
28
International Laboratory for Research on Animal Diseases (ILRAD).
29
30
Murray, M., Trail, J.C.M., Turner, D.A. and Wissocq,Y., 1983. Livestock Productivity and
31
Trypanosomiasis. Network Training Manual. International Livestock Centre for Afiica. Addis
32
Ababa, Ethiopia.
33
34
Rowlands, G.J., Woudyalew Mulatu, Authié, E., d’ieteren, G.D.M., Leak, S.G.A., Nagda,
35
S.M. and Peregrine, A.S., 1993. Epidemiology of bovine trypanosomiasis in the Ghibe valley,
36
Southwest Ethiopia. 2. Factors associated with variations in trypanosome prevalence,
37
incidence of new infection and prevalence of recurrent infections. Acta Tropica, 53, 135-150
38
39
Sanyang, F.B., Wagner, H.-G.R. and Clifford, D.J., 1995. Influence of suckling on calving
40
interval of Ndama cows in The Gambia. Tropical Animal Health and Production, 27: 191-l 92
41
42
SAS Institute Inc., 1989, SASSTAT User’s Guide, Version 6, Fourth Edition, Volume 2,
43
Cary, NC: SAS Institute Inc., 1989. 846pp
44
45
Stephen, L.E., 1986. Trvpanosomiasis, a veterinarv perspective. Pergamon Press. Oxford,
46
England.
47
48
Thorpe, W., Coulibaly, L., Defly, A., d’Ieteren, G.D.M., Feron, A. Grundler, G. Hecker, P,
49
Itty, P., Maehf, J.H.H., Mawuena, K., Morkramer, G., Mulungo, M., Nagda, S.M., Paling,
50
R.W., Pelo, M., Rarieya, J.M., Shuetterle, A. and Trail, J.C.M., 1988. Facterus influençant les
5 1
performances de reproduction dans diverses situations du réseau. In Production Animale dans
t
11
1
les R&ions d’Afrique Infestées par les Glossines. Compte rendu réunion, 23-27 Novembre
2
1987, Nairobi, Kenya. Centre International pour 1’Elevage (CIPEA).
Table 1. Number of flies caught, number of flies dissected , unadjusted mean (*SD) yearly
number of Glossina morsitans submorsitans and Glossina nalnalis gambiensis caught per trap
per day, flies infection rates by Trypanosoma congonlense and Trvnanosoma vivax, and tsetse
challenge index (tsetse infection x number of flies caught per trap per day) at Kolda fi-om
march 1988 to march 1992.
~---
No.
No. flies
FTD’
FIR2
TC13
months cawht
dissected
Year
1988 10
2528
1546
6.1
2.1
21.1
1989 12
3968
2120
8.4
1.7
18.2
1990 11
2879
1121
6.4
4.8
33.7
1991 12
835
292
1.9
1.0
0.9
1992 3
84
29
0.8
2.8
0.1
7
8
1: FTD: Fly per trap per day; 2: FIR: Fly infection rates; 3: TCI: tsetse challenge index
1 3
1
Table 2.
Least square means infection rates with Trypanosoma congodense and
2
Trypanosoma vivax and packed ce11 volume (PCV %) in Ndama cattle kept under village
3
m
between 1999 and 1992.
-_x---m*
Source of variation
Trypanosome infection
Packed ce11 volume (%)
rate(%)
rl
mean f s.e.m
--IIxII.~-_--_l-..
n
mean f s.e.m
e...-----
Overall mean
9905
2.5 f 0.51
5972
27.7 If: 0.27
-
Year: ***
1988
259
1.4 f 1.2
210
30.5 f 0.43
1989
1458
2.4 f 0.6
1014
29.1 f 0.29
1990
1137
3.2 f 0.7
792
26.2 f 0.31
1991
3396
3.1 f 0.5
2151
26.4 f 0.27
1992
3655
2.4 f 0.6
1805
26.1 f 0.28
Sex ***
Female
6772
2.8 f 0.3
3589
27.5 f 0.23
Entire male
2968
3.4 f 0.4
2286
26.4 f 0.23
Castrated male
165
1.3 f 0.3
97
29.1 jz 0.23
Age ***
< 1 year
1586
1.9 f 0.7
1327
27.9 A 0.29
l-3 year
3398
1.9 * 0.5
2741
27.4 f 0.29
> 3 year
4921
3.6 * 0.5
1904
27.7 f 0.27
Strongyle infection (P= 0.08)
Negative
4127
28.0 f 0.29
Positive
1889
27.3 f 0.38
Trypanosome infection * **
Negative
5866
29.3 f 0.18
Positive
150
26.0 f 0.44
Tryp. x Strongyle infection
Negative
Negative
4025
29.7 f 0.19
Negative
Positive
1841
28.9 f 0.19
Positive
Negative
102
26.4 -f 0.48
Positive
Positive
4 8
25.7 f 0.69
4
Significance levels : *** P<O.Ol
14
1
Figure 1. Monthly tsetse challenge index and cattle infection rates with T. congonlense and T.
2
vivax
3
4
/----
45
40
35
J
F
M
A
M
J
J
A
S
O
N
D
5
/--
-
6
7
8
9
Figure 2. Mean monthly strongyle prevalence and egg output in Ndama cattle
1 0
600
Ê
E. 500
6 0
=
2
$j
5 0
400
L
ô
Y
2
40 fj
2 300
E
i!
3 0 8
g)
0.
200
8,
2 0
P
P 1 0 0
W
1 0
0
J F M A M J J A S
01 N D
Month
11
1 5
1
2
Figure 3. Monthly packed ce11 volume (PCV, %) and trypanosome prevalence in village
3
Ndama cattle between 1988 to 1992.
4
3 0
‘
,
’
I
\\-
I
I
I
,
I
.
I
2 6
J
F M A M J
J A S 0 N D
Month
5
1 6
Tsetse challenge, trypanosome and helminth prevalences, and productivity of village
2
Ndama cattle in Senegal
3
A. Fa11’,2 , A. Diack’, A. Diaité3, M. Seye3 and G.D.M. d’Ieteren4
4
‘Institut Sénégalais de Recherches Agricoles, CRZI Kolda , BP 52, Kolda, Senegal.
5
2Centre for Tropical Veterinary Medicine. Easter Bush Roslin, Midlothian, EH25 9RG, Scotland
6
31nstitut Sénégalais de Recherches Agricoles, LNE;RV, BP 2057, Dakar, Senegal
7
41ntemational
Livestock Research Institute, P.O. Box 30 709, Nairobi, Kenya
8
Ahstract
9
Data on tsetse fly, and on village Ndama cattle collected over a 4-year period in southem Senegal, were analysed.
10
A total of 531 Ndama came in 4 herds of 3 villages in the Kolda area were monitored monthly. Glossina
11
morsitans submorsitans and Glossina nalnalis nambiensis are present in the study area. Mean tsetse apparent
12
density was 5.4 flies/trap/day.
Trypanosome (Trypanosoma conyonlense
and Trvuanosoma vivax) infection rate
13
in flies was 2.5(s.e. 0.37)%. Tsetse challenge index was 17.3(s.e. 4.18). Mean monthly trypanosome prevalence
14
in came was 2.5(s.e. 0.51)%. Highest trypanosome prevalence occurred during the dry season, and animals less
15
than 1 year old were more frequently infected than older animals. The linear relationship between the loglO+l
16
tsetse challenge and the arcsine of the trypanosome prevalence was significant only when mean monthly values
17
of these variables over the 4-year period were used with tsetse challenge preceding infection rate by 3 months.
18
Mean monthly prevalence of strongyle, strongyloides, ascaridia and coccidia were 34.4(s.e. 0.60), 2.l(s.e. 0.18),
19
1.2(s.e. 0.45) and 15.6(s.e. 0.47)%, respectively. Calf mortality rate at 1, 6 and 12 months of age was 2.l(s.e.
20
2.1), 5.2(s.e. 2.8) and 12.2(s.e. 3.3)%, respectively. Calving interval (584 s.e. 58 days) was not influenced
by
21
trypanosome status of the cow during lactation. Calving interval was shorter by 167 days when the calf died
22
before one year of age in comparison
to calving intervals for which the calf survived beyond one year. Live
23
weight at birth, 6 and 12 months of age were 15.8(s.e. 0.54), 48.X(s.e. 2.56) and 71.l(s.e. 5.44) kg, respectively.
24
Mean lactation length, total and daily milk offtake were 389(s.e. 16) days, 231(s.e. 15) litres and 0.69(s.e. 0.037)
25
litres, respectively. Trypanosome infection during lactation did have a significant effect on the amount of milk
26
extracted for human consumption
nor did trypanosome status affect calf growth.
27
Key words: Ndama came, tsetse challenge, trypanosomiasis,
helminthiasis, productivity, Senegal.
28
29
Introduction
30
Because of their trypanotolerance, Ndama cattle constitute a unique animal genetic resource
31
which forms the basis of large ruminant agriculture in many parts of West Africa where the
32
risk of trypanosomiasis is high. The Ndama cattle breed are a multipurpose breed that produce
33
milk, meat, power and manure and therefore contribute a great deal to the income and welfare
34
of millions of farmers in mixed trop-livestock production systems in West Afiica. However a
35
complex set of technical factors related to health, nutrition and management constrain the
36
productivity of Ndama cattle kept under traditional husbandry systems. The relative
37
importance of these factors needs to be determined i.f strategies to make better use of this
38
genetic resource are to be developed to meet the growing demand for animal products in West
39
Africa. TO this end, an epidemiological study was carried out from 1988 to 1992 in the
40
Casamance region of southem Senegal to investigate causes of variation of Ndama cattle
41
productivity and the stability of the trypanotolerance trait under village management systems.
42
This study was part of a large epidemiological programme that was conducted by International
43
Livestock Centre for Africa (ILCA now ILRI) and National Agricultural Research Institutes in
44
many sites in Africa with different degrees of trypanosomiasis risk. This paper reports fïndings
45
on the tsetse challenge, prevalence of parasitic diseases (helminthisiasis, trypanosomiasis) in
46
village Ndama cattle in southern Senegal and
how these factors affect reproduction
47
performance, calf growth and milk production.
48
49
50
51
52
53
54
Correspondance address: Dr Abdou FAL(L Institut Senegalais de Recherches Agricoles, Laboratoire National
55
d’Elevage et de Recherches Vétérinaires, BP 2057, Dakar, Senegal, Tel (221) 832 3678, Fax (221) 832 2118
1
Materials and Methods
2
The study area
3
The study was carried out in the region of Casamance in Southem Senegal. The climate in this
4
region is of a sudano-guinean type and annual rainfall during this study at Kolda was 1018,
5
1045, 787, and 684 mm in 1988, 1989, 1990 and 1991., respectively. The unimodal rainfall at
6
Kolda occurs between June and October. Four herds in three villages (Salamata, Yassiriba,
7
Sare Pathe) were selected for the evaluation of Ndama cattle health characteristics and the
8
estimation of production parameters. Salamata and Yassiriba are along the Mahon forest
9
boundaries and close to a stream. Sare Pathe is located in the forest of Bakor.
1 0
11
Herd management
1 2
Multipurpose Ndama cattle are kept in the mixed trop-livestock farming system at Kolda as a
1 3
supplier of food (milk), cash through offiake for meat, power for cropping and transport, and
1 4
for manure for the restoration of soi1 fertility. Animals belonging to many individuals form a
1 5
herd which is under the responsibility of the head of a household. Animals graze natural
1 6
pastures which form the main source of the food supply. Pastures are abundant and are of good
1 7
quality during the rainy season and early dry season. After the grain harvest, animals have
1 8
access to upland (millet, sorghum) and lowland (rice) trop residues that are consumed directly
1 9
in the fields. Shortage of food supply during the critical months of March, April, May and
20
June is the single most important constraint that face herd owners in this area.
2 1
22
Animals are tethered individually ovemight in a trop fïelds during the dry season and are
23
moved to the forest during the cropping season to avoid damage to crops. Mating is not
24
controlled and calving occurs a11 year round. However peak calving is recorded in July and
25
August. Milking is performed once a day, and begins one week afier calving. The calf is
26
allowed to suckle its dam for a few seconds to trigger milk let-down and thereafter, is tethered
27
at the foot of the dam during the course of milking. The residual milk is suckled by the calf.
28
Suckling of calves takes places a second time in the evening when adult animals retum from
29
grazing. Calves are tethered over night to prevent suckling. They also graze separately from
30
adults in areas surrounding homesteads. A main feature of the milking system in the Kolda
31
area is that milking for human consumption is suspended during part of the dry season and is
32
resumed during the next wet season.
33
Experimen ta1 design
34
This study was carried out over a 4-year period (1988 to 1992). Data was collected
35
concomitantly on tsetse challenge, animal health and animal production parameters.
36
37
Animais
38
A total of 531 Ndama cattle kept in 4 herds of 3 villages were monitored monthly for 52
39
months in Salamata and Yassiriba with 163 animals, and for 24 months in Sare Pathe with 268
40
animals. Animals were individually tagged on both ears. At the start of the programme each
41
anima& age and the number of calving of each adult female were estimated by farmers.
42
Animals were managed under traditional village conditions and therefore were subjected to
43
natural tsetse challenge. Routine vaccination against rinderpest, anthrax, hemorrhagic
44
septicaemia, and contagious bovine pleuropneumonia was given. Animals were also treated
45
with diminazene aceturate (Berenil, 3.5 mg kg-’ body weight) when trypanosomes
were
46
detected and the packed red ce11 volume (PCV) was below 20%.
47
48
Field recording and laboratory determinations
49
Monitoring of tsetse flies
50
Twelve biconical traps, as described by Challier and Laveissière (1973), were placed at each
5 1
site each month for 3 consecutive days and harvested every 24 hours. Traps were set 100 m
2
apart from each other. Furthermore they were distributed in Savannah and river-me areas within
2
the forests of Bakor and Mahon which constitute common grazing areas for cattle from
3
surrounding villages. Al1 flies caught were identified and recorded with reference to biotope,
4
species, sex, teneral/non-teneral status, and age group by wing-fi-ay method as described by
5
Jackson(l946). Al1 live non-teneral flies were then dissected in a 0.9% saline solution and the
6
midgut, labrum, hypopharynx and the salivary glands were examined for the presence of
7
trypanosomes by phase-contrast microscopy at 320x magnification using a combination of
8
Periplan 10x eyepieces and a long-distance L32 objective.
9
10
Cattle herd monitoring
11
Each month, immediately following the tsetse trapping on the site, blood samples were
1 2
collected from the jugular vein of the cattle into evacuated tubes containing EDTA. The PCV
1 3
was measured and the level of parasitaemia estimated -using phase-contrast examination of the
1 4
blood buffl-coat (Murray et al., 1983). Whenever the PVC declined below 20%, blood smears
1 5
were made in order to determine if other hemoparasites (e.g., babesia spp, anaplasma spp.)
16
were present. Faeces samples were collected from the animal’s rectum for the entire herd every
1 7
3 months and monthly for animals aged O-3 years. Faecal samples were immediately examined
1 8
for the presence of gastro-intestinal parasites using the McMaster Egg-counting technique
1 9
(Murray et al., 1983). Animals were weighed each month using an electronic scale (Barlo,
20
Australia) and milk offtake for human consumption was measured using a graduated tube.
2 1
Information on herd dynamics including date of birth, mortality and animal transactions (e.g.,
22
purchases, sales, exchanges and transfers) were routinely collected during weekly herd visits.
23
24
Data analysis
25
Data was analysed using SAS General Linear Mode1 procedures (SAS, 1989). A regression
26
analysis of the arcsine of trypanosome prevalence on L,oglO+l of the challenge index (CI), the
27
product of the apparent density and the infection rate of flies, was performed to investigate the
28
relationship between these two variables. Village and herd within village, month and year the
29
observation was made, age category (category 1: < 1 year, category 2: 1 to 3 years, category 3:
30
>3 years) and sex of the animal (female, entire male, castrated male) were included in a11
3 1
analyses of health parameters and production traits. Specific additional factors were also
32
included as necessary. Additional sources of variation for the analysis of trypanosome
33
prevalence included the level of infection with strongyle parasites ( level 1: 0 egg per gram of
34
faeces (epg), leve12: 100-500 epg, leve13: > 500 epg).
35
36
The analysis of PCV included the trypanosomiasis status of the animal and the interaction
37
between trypanosome and helminthiasis infections. The data set used to investigate the effects
38
of these factors on PCV was formed by using data from animals for which both faecal and
39
blood samples were taken and analysed for the determination of blood and gastro-intestinal
40
parasites. Also, the data set used to analyse PCV excluded data from 49 animals which were
41
infected with babesia or anaplasma. These animals ha.d a mean PCV of 19 (S.D. 10) %. This
42
was intended to exclude the influence of these diseases on the evolution of anaemia and
43
therefore to improve estimates of PCV based on factors included in the statistical model.
44
45
For the analysis of calving interval, the effects of parity of the previous parturition and the
46
trypanosome status of the cow were investigated. Calving number was classified into two
47
groups, with group 1 formed by parturition number 1 and 2, and group 2 composed of cows
48
with 3 or more calvings. Cows were also grouped into non-infected and infected with
49
trypanosomes after the fïrst parturition of the inter-val. Trypanosome status was also included
50
in the analysis of calves live weight (LW) growth up to the age of 12 months. Two classes of
3
infection status (non-infected and infected at least once with trypanosomes), between the age
2
of 0 to 6 months and between 6 to 12 months, were formed.
3
4
For the analysis of lactation length, total and daily milk for human consumption, the following
5
classes of factors were included: 3 seasons of calving (season 1, the wet season: June, July,
6
August, September with minimum and maximum ambient temperatures of 24 and 34 “C,
7
season 2: the cool dry season, October, November, December with minimum and maximum
8
ambient temperatures of 18 and 35 “C and season 3, the hot dry season, February, March,
9
April, May, with minimum and maximum ambient temperatures of 21 and 39 “C), 2 levels of
10
infection status (non-infected and infected at least once during lactation irrespective of the
11
time during lactation when infection occurred), the interaction between season and infection
12
status, and 2 types of milk extraction practices (continuous milk extraction throughout
13
lactation, and suspension, and later resumption of milk offtake).
14
15
Mean calving intervals and cow survival rate, calf mortality rate, calf live weight at one year,
16
and milk offiake for human consumption, were combined to determine productivity indices as
17
described by Agyemang et al. (1991).
18
19
Results
20
Tsetse challenge
21
Tsetse flies present in the study area were identified as G. m. submorsitans and G. n.
22
gambiensis. Out of the 10,210 flies caught from Marc11 1988 to March 1992, 64% were G. m.
23
submorsitans and 36% were G. D. gambiensis. The number of flies caught per trap per day is
24
an estimate of the apparent density of tsetse flies and the average apparent density found in
25
this study was 5.4 flies/trap/day. Although the apparent density was highest between January
26
and April with a peak in February the two tsetse species showed different patterns of
27
distribution over the year. The number of G. p. Gambiensis trapped was highest during the
28
rainy season (June to September) and during the first months of the dry season (November,
29
December, January) whereas most of catches of G. m. submorsitans occurred during the
30
second half of the dry season (February and May). Finally, there were more marked seasonal
31
changes in the distribution of G. m. submorsitans than in that for G. D. aambiensis.
32
33
The dissection of 50% of caught flies gave a mean monthly infection rate by T. congolense a
34
T. vivax of 2.4 (s.e. 0.37)% during the 4-year period of the monitoring programme. Mean
35
monthly CI, an estimate of the trypanosomiasis risk, was 17.3 (s.e. 4.18). Figure 1 shows the
36
seasonal pattern of changes in CI. Tsetse challenge was more pronounced hem January to
37
April, peaked in March and decreased gradually as the dry season progressed. Lowest CIs
38
were recorded during the rainy season. There was a Sharp decrease in tsetse apparent density in
39
1991 and 1992 compared to 1988 and 1990.
40
41
Trypanosomiasis infection rates in Ndama cattle
42
The overall mean trypanosome prevalence was 2.5(s.e. 0.51)%. Infection rates due to T,
43
congolense and T. vivax were 1.89(s.e. 0.43) and 0.64(:s.e. 0.27)%, respectively. Trypanosome
44
infection rates were signifïcantly affected by village (Pc O.OOl), month of the year (P<O.Ol)
45
and age of the animal (P<O.OOl). The monthly relative number of animals infected with
46
trypanosomes was larger in Yassiriba (4.3 s.e. 0.68 %) than in Salamata (1.5 s.e. 0.54 %) or
47
Sare Pathe (1.7 s.e. 0.59%). Figure 3 shows seasonal variation in trypanosome prevalence.
48
Trypanosome infection rates increased steadily each year fiom January, during the dry season,
49
and peaked in June, the end of the dry season. A gradua1 decrease of the infection rates was
50
then observed from June, during the rainy season. Lowest infection rates were recorded in
51
December and January.
4
Figure 3 shows that there was a time lag of 3 months between peak of the trypanosome
2
prevalence and that of the tsetse challenge. When the log+l of the monthly tsetse challenge
3
was regressed on the arcsine of the mean monthly infection rates aggregated over the 4-year
4
period, significant relationship (R2 = 0.52, PcO.01) was detected between these two factors.
5
However this relationship was no longer significant when the 48 monthly infection rates and
6
monthly tsetse challenges were used in the regression analysis.
7
8
Adult animals aged more than 3 years were more affected by trypanosomes (3.6 s.e. 0.5 %)
9
than younger animals (1.9 s.e. 0.5 %).
Although the effect of strongyle infection on
1 0
trypanosome infection rates was not signifïcant (PI> 0.05), animals which were heavily
11
infected with strongyle tended to be more infected with trypanosomes (epg > 500 epg,
1 2
trypanosome infection rate = 3.8 s.e. 1.01 %) than those with medium infestation (epg = lOO-
1 3
500 epg, trypanosome infection rate = 2.5 s.e. 0.69 %) or those which were strongyle free
1 4
(trypanosome infection rate = 2.6 s.e. 0.62 %,). Castrated males tended also to be less infected
1 5
with trypanosomes than both entire males and females (Table 2) but the difference was not
16
significant (P= 0.16).
1 7
1 8
Gastro-intestinal parasites
1 9
The analysis of 6,016 animal-month faecal samples gave a mean monthly prevalence of 34.4
20
(s.e. 0.60), 2.1 (s.e. 0.18), 1.2(s.e. 0.45) and 15.6(s.e. 0.47)Oh for strongyle, strongyloides,
2 1
ascaridia and coccidia types of infestation, respectively.
22
23
Figure 2 shows seasonal variations of strongyle infection and worm burden. Strongyle
24
prevalence and egg output were lowest during the dry months of January to May. The number
25
of animals infested with strongylidae increased gradually each year from April to reach a peak
26
in June and remained high (>40%) in July, August and September, the wettest months of the
27
year. The worm burden followed the same pattern, but its peak occurred in September, 3
28
months later than the peak of strongyle prevalence.
29
30
Mean strongyle egg counts were higher in animals less than 1 year old (epg = 346 se. 47)
31
than in animals l-3 years old (epg = 286 s.e. 43), or in animals more than 3 years old (epg =
32
220 se. 44). For animals carrying strongyle-type parasites, worm burden tended to be heavier
33
in those infected (epg = 318 s.e. 75) in comparison to those not infected with trypanosomes
34
(epg = 250 s.e. 20), but the difference was not significant. It has also been noted that
35
strongyloides prevalence was higher in animals infected (4.4 se 0.35%) than in animals not
36
infected (1.9 s.e. 0.35%) with trypanosomes. Age had a significant effect on prevalence of
37
ascaridia and strongyloidae. Young animals less than 1 year old were more frequently infected
38
with than older animals. Ascaridia were rare in animals between 1 and 3 years old and were
39
absent in animals more than 3 years old. The prevalence of strongyloides was also lower in
40
animals more the 1 year old (1.8 s.e. 0.74%) than in animals less than 1 year old (5.8 s.e. 0.80
4 1
%). Although adult animals were free of ascaridia and strongyloides, the prevalence of
42
strongyle-type infestation was almost as high (34 s.e. 2.5%) as in Young animals (36 s.e. 2.7).
43
44
Packed ce11 volume
45
Packed ce11 volume, which is an indication of the degrele of anaemia, was significantly affected
46
by the year (PcO.01) and month (PcO.01) during which PCV was determined, sex (PcO.01)
47
and age (PcO.01) of the animal, and trypanosome infection (PcO.01). In general there was
48
trend of a decline of PCV from 1988 to 1992 (Table 2). Each year, PCV reached its peak in
49
February and the lowest values were recorded from May to October, coinciding with the end
50
of the dry season and the rainy season (Figure 3). Highest PCVs were recorded each year fi-om
5 1
November to February, with peak values reached in February. Thereafter, there was a Sharp
5
decrease of PCV values from February to May. This period coincided with the time when food
supply was critical and when significant increases in trypanosome infection rates were seen.
In general there was a decline in PCV values of 3.3 % in animals infected with trypanosomes
as compared to those not infected. Castrated males had higher PCV than entire males or
females. The effect of strongyle infection was close to signifïcance levels (P=O.O8). In general
strongyle-free animals had higher PCV than infected animals. Although the effect of the
8
interaction between strongyle and trypanosome infections was not signifïcant, PCV values
9
shown in table 2 suggest an additive effect of these infections on the development of anaemia.
1 0
11
Production parameters
1 2
Mortality rates
1 3
Out of the 225 calves bom during the course of the monitor-mg programme, 2.1 (se. 2.1), 5.2
1 4
(s.e. 2.8) and 12.2 ( s.e. 3.3%) died before the age of 1, 6 and 12 months, respectively. The
1 5
effect of herd on mortality rates at 1 and 6 months of age was signifïcant (PcO.05). Sex of the
1 6
animal, year and month of birth and parity did not signifïcantly influence mortality rates.
1 7
1 8
Calving in tervals
1 9
Sixty eight calving inter-vals of cows that gave birth in 1988, 1989 and 1990 were analysed.
20
The unadjusted mean calving interval was 634 (S.D. 186) days. The least square mean calving
2 1
interval was 584 (s.e. 58) days. Year and parity of previous parturition and calf survival to 1
22
year had significant effects (PcO.05) on calving inter-val. Cows whose calf died before the age
23
of 12 months had calving intervals shorter (by 167 days) than that of cows whose offspring
24
survived beyond 12 months of age.
25
26
The trypanosomiasis status of cows did not affect significantly calving inter-vals. When the
27
previous calving number was 1 or 2, the calving interval was greater by 98 days than when
28
previous calving number was greater or equal to 3. Mean calving inter-vals were 663 (s.e. 78),
29
493(s .e. 73) and 445(s.e. 65) days for cows that calved previously in 1988, 1989 and 1990,
30
respectively.
31
32
33
Live weight changes
34
Live weight at birth, 6 and 12 months of age were 15.8 (s.e. 0.54), 48.l(s.e.2.56) and 71.lts.e.
35
5.44) kg, respectively. Only the season of calving had a significant effect on calf weight at 6
36
months of age. Calves bom during the late dry season (February to May) were lighter (PcO.05,
37
42.9 s.e. 3.48 kg) than those bom during the wet season (50.5 s.e. 2.95 kg) or in the early dry
38
season (50.7 s.e. 3.09 kg). Trypanosome infection status did influence significantly calf live
39
weight at 6 or 12 months of age.
40
4 1
The average LW of empty cows was 222(s.e. 1.3) kg. However there was marked seasonal
42
fluctuation of cow LW during the year. Cows lost LW during the second half of the dry
43
season, from March to June and they gained LW progressively during the wet season, but it
44
was until November, the early dry season, that they fùlly recovered their LW. The magnitude
45
of LW losses between the highest LW in November and the lowest LW in June was an
46
average of 25 kg.
47
48
Lactation characteristics
49
Milk extraction was suspended during the dry season in 42% of lactating cows that were
50
subjected to milk recording. The average number of days milking was suspended was 127 days
5 1
with a minimum of 52 and a maximum of 298 days.
6
1
2
Mean lactation length, total milk extracted for human consumption and daily milk offtake
3
were 389(s.e. 16) days, 231(s.e. 15) litres and 0.69(s.e. 0.037) litres, respectively. However
4
season of calving had a significant effect (PcO.01) on lactation length. Lactation length was
5
longer when calving occurred during the wet season (season 1: June to September: 446 s.e. 18
6
days) than when calving took place during the early dry season (season 2: October to January:
7
358 s.e. 23 days) or during the late dry season (season 3: February to May: 365 s.e. 33 days).
8
Cows for which milk offtake was suspended had a longer lactation length (452 s.e. 18) days)
9
than cows that were continuously milked (327 s.e. 20 days). Total milk extracted for human
1 0
consumption was affected by calving season and herd. Cows that calved in season 1, the wet
1 1
season, out-produced (264 se. 17 litres) cows that gave birth during the dry season (seasons 2
1 2
and 3). Cows starting lactation in season 2 and 3 produced 188 (s.e. 22) and 240 (s.e. 31)
1 3
litres, respectively.
1 4
1 5
The interaction between season of calving and trypanosome infection on lactation length was
1 6
significant (PcO.05).
Cows that gave birth between February and May and that were infected
1 7
with trypanosomes during lactation had the shortest lactation length of 318 (s.e. 60) days.
1 8
Trypanosome infection did not appear to affect lactation length when calving occurred in the
1 9
wet season or in the early dry season. Total and daily milk offtake appeared also to be minimal
20
in cows that calved between February and May and that were infected with trypanosomes
2 1
during lactation, but these differences were not significant. When calving occurred between
22
October and January and the cows were detected parasitaemic, total and daily milk offtake
2 3
were 166(s.e. 36) and 0.560(s.e. 0.09) litres, respectively. In contrast cows that calved in the
24
same period but that were not detected parasitaemic produced 210(s.e. 18) litres during the
2 5
entire lactation and 0.740 (s.e. 0.044) litres per day. Trypanosome infections that occurred
26
during the wet season or during the last part of the dry season did not seem to affect milk
2 7
offtake. Total milk offtake of non-infected and infected cows that started lactation between
2 8
February to June were 242(s.e. 23) and 238(s.e. 56) litres, respectively.
29
30
Productivity indices
3 1
Mean calving inter-val (584 days), cow survival rate ( 98.5% per year), calf survival rate (88 %
32
per year), calf LW at one year of age (71 .l kg), and milk offtake during the first 12 months of
3 3
lactation (216 kg) found in this study were combined t:o produce productivity indices. Index 1
34
which is the amount of one-year old calf LW plus the LW equivalent of milk extracted for
3 5
human consumption produced per cow per year was 62.8 kg. Index 2, the LW of one-year old
36
calf produced plus LW equivalent of milk offtake per 100 kg of cow maintained per year was
3 7
28.8 kg. Index 3, the LW of a one-year old calf produced plus LW equivalent of milk offtake
3 8
per 100 kg of cow metabolic LW was 120.8 kg.
39
40
Discussion
4 1
In the present study, the population of tsetse flies decreased over the experimental period. The
42
apparent density of tsetse flies was particularly low in 1991 and 1992 as compared to previous
4 3
years. These changes in the population of flies may be attributed to the effect of continuous
44
trapping for 4 years in the same site. Another contributing factor to the decline of the tsetse
4.5
population could have been the reduced rainfall recorded during 1991 and 1992 and also the
46
occurrence of bush-fïres which may have destroyed fly habitat or caused migration of the fly
47
population. However, the decline in the challenge index in 1991 and 1992 did not translate
48
into reduced trypanosome infection rates in cattle during these years. The regression of the
49
monthly trypanosome infection rates on the monthly challenge index after a log transformation
5 0
of tsetse challenge and arcsine transformation of trypanosome infection rates showed a
51
significant correlation between these two parameters. However, cor-relation was only apparent
when data was aggregated over the 4-year period and that challenge preceded the prevalence
2
data by three months. The correlation of these two parameters on a monthly basis year by year
3
failed to detect any Sign&ant relationship betwee:n these two factors. The absence of
4
signifïcance relationship was even apparent when the moving average of the tsetse challenge
5
was used in the regressions analysis. There were many months when the number of flies
6
caught was zero in 1991 and 1992, but trypanosomes were detected in the blood of the
7
animals. This suggests that although the challenge index in a simple field estimate the
8
seriousness of trypanosomiasis in an area, it may fail to give valid assessment of the problem
9
if data is collected for a short period of time or if there are many months when the challenge
1 0
index is zero. Even when the index is zero it does not mean that flies are totally absent.
1 1
Vectors other than G. m. submorsitans and G. p. gambiensis may also have played a role in
1 2
the transmission of trypanosomes to cattle.
1 3
1 4
Mean trypanosome prevalence (2.5%) found in the present study is relatively low. Animals in
1 5
Yassiriba were more frequently infected with trypanosomes than those in Yassiriba and Sare
1 6
Pathe. The herd size in Yassiriba was smaller than in other villages. This, coupled with the fact
1 7
that Yassiriba was located deeper in the forest and at the vicinity of a stream may have created
1 8
conditions for animals in Yassiriba to be more exposed to tsetse flies than in other villages
1 9
where these conditions did not occur.
20
2 1
In the present study there was an increase in the trypanosome prevalence as animals aged. The
2 2
higher capacity of Young animais to resist trypanosomiasis relative to adult animals has
2 3
already been reported (Stephen, 1986; Rowlands et al., 1993) and is suggested to be related to
24
the superior erythropoeitic response of younger animals (Murray, 1988). However as
2 5
suggested by Rowlands et al. (1993), differences in exposure may contribute to these variation
26
in trypanosome prevalence in animals of different age classes. In this study castrated males
2 7
were also less subjected to trypanosome infection than entire males and females. It would have
2 8
been thought that being used for work, the physical stress castrated males undergo during work
29
would increase their susceptibility to infection. It is likely that both Young animals and
30
castrated males are less infected than other categories of animals because of differences in
3 1
their respective management. Not only are draught animals better fed during the dry season but
3 2
also both Young animals and draught animals graze at the vicinity of homesteads and are not
3 3
watered in gallery forest where contact with flies is more likely.
3 4
3 5
The time lag between peaks of tsetse challenge and trypanosome prevalence in cattle found in
36
this study is similar to that reported in studies in Ethiopia (Rowlands et al., 1993) and the
3 7
Gambia (Claxton, 1992). This is supposedly due to the time interval between the infective bite
3 8
and the detection of trypanosomes in the animals (Leak et al, 1993).
3 9
40
In this study, heavy strongyle burden was conducive to increased trypanosomiasis
4 1
susceptibility. The same finding is reported in Ndama cattle in the Gambia (Dwinger et al.,
42
1994).
4 3
44
Although this study showed a significant relationship between trypanosome prevalence and
4 5
tsetse challenge, the seasonal variations of trypanosome infection rates suggests also that
46
nutrition could be a confounding factor. Indeed, increases in trypanosome prevalence during
47
the dry season, from January to June, coincided with poor nutrition during that period and the
48
consequent reduction in animal LW and PCV%. Work done in the Gambia showed that
49
nutritional stress depresses the capacity of the animals to tope with trypanosome infections
5 0
(Little et al., 1994).
5 1
8
B<
’
.
1
The present study has also provided information on the epidemiology of helminthiasis in
2
Ndama cattle in southern Senegal. Infestations with strongyle-type parasites were more
3
fi-equent and the worm burden was heavier in the wet season than in the dry season. In general
4
adult animals appeared as frequently infested with strongyle parasites as younger animals and
5
therefore constitute a source of contamination of pastures. Studies in the Gambia revealed the
6
same epidemiological characteristics of gastrointestinal nematodes in Ndama cattle (Kaufmann
7
and Pfïster, 1990). It has also been demonstrated in the Gambia (Kaufmann and Pfister, 1990)
8
that Heamoncus contortus is the most frequent strongyle, which cari cause severe anaemia,
9
pastures are f?ee of infective larvae during the dry season and third, pasture recontamination in
1 0
the early wet season is caused by the development of inhibited Heamoncus larvae and residual
1 1
adult worms. Results from the present study suggest also that an interaction exists between
1 2
trypanosome and helminthiasis infections. Trypanosomiasis was more frequent in animals
1 3
heavily infested with strongyle parasites. The decline in PCV in animals infested with
1 4
strongyles seen in this study suggests that strongyle infestation may depress the capacity of
1 5
Ndama cattle to withstand trypanosome infections. Such an influence of helminth infections
1 6
on the susceptibility to trypanosomiasis is reported in the Gambia (Dwinger et al., 1994).
1 7
1 8
Additionna1 work in this study has also shown that when calving occurred during the late dry
1 9
season calves had a slow growth rate up to 6 months of age. Growth of calves born during this
20
period was impaired by low milk output of the dam due to poor nutrition. Trypanosome
2 1
infection did not signifïcantly affect calf growth. This, coupled with the fact that higher PCV
2 2
seen in animals younger than 1 year as compared to older animals and therefore their better
2 3
ability to resist anaemia, give further evidence of the capacity of Young animals to be more
24
resistant to trypanosomiasis than adult animals.
2 5
2 6
Although previous studies (Agyemang et al., 1993) bave indicated the depressing effect of
2 7
trypanosome infection on reproductive performance, in the present study calving interval was
2 8
not affected by the trypanosome status of Ndama cows during lactation. This finding is in
29
agreement that of Thorpe et al. (1988). The most important factor that influenced the
3 0
reproductive performance in the work described here was whether the calf survived or not up
3 1
to 12 months of age. The calving inter-val of cows whose calf died before the age of 12 months
32
was lower by 167 days than that of cows that suckle their offspring over 12 months. Indeed,
3 3
the depressing effect of suckling on post-partum cyclicity of Ndama cows is reported by
34
Sanyang u.(1995). As pointed out by Thorpe et al. (1988), use of calving interval as an
3 5
estimate of reproductive performance fail to take into account non-fertile cows in the herd and
36
this may mask the effect of trypanosome infections on reproductive performance.
37
38
The mean lactation length (389 s.e. 16 days) and total milk for human consumption (231 s.e.
39
15 litres) found in this study carried out in southern Senegal where milking is done once a day
40
agree with the level of lactation performance by Ndama cows milked once daily in the
4 1
Gambia. Lactation length and milk offtake were 437(s.e. 16.6) days and 239(s.e. 19.3) litres in
42
the once-daily milking system in the Gambia (Agyemang, et al., 1991). Trypanosome
4 3
infection did not affect lactation length or total milk offtake. This again agrees with results
44
obtained in the Gambia where non-infected cows out-produced infected cows during lactation
4 5
by only 24 kg during a 14-month location period and this difference was not signifïcant
46
(Agyemang, et al., 1991). However trypanosome infection caused a reduction in milk
47
production during the 6 months following infection in Ndama cows in The Gambia
48
(Agyemang et al., 1990).
49
50
Larger lactation length and greater milk offtake seen in cows starting lactation during the wet
5 1
season when food was plentiful and of good quality as compared to the dry season, suggest
9
1
that nutrition is the driving factor that determines milk production of village Ndama CO~S.
2
Cows calving during the last part of the dry season performed better than those calving during
3
the early part of the dry season. For the latter, most of the lactation length occurred during dry
4
months whereas the former Will benefït fi-om the pastures improvement in the next wet season.
5
In terms of milk production, cows that gave birth between November and January were more
6
severely affected by food shortage than cows calving; in other seasons. Feed restriction was
7
compounded in these cows by trypanosome infections and led to the shortest lactation length.
8
The trends observed regarding the interaction of season of calving and trypanosome infection
9
on milk offtake suggest that well fed Ndama cows could produce milk with a no major
1 0
negative influence of trypanosome infection. Similarly, Agyemang et al. (1990) suggested that
1 1
the depressive effect of trypanosome infections on milk production could be reduced through
1 2
the provision of additional food to cattle showing signs of the disease.
1 3
1 4
Finally, the productivity indices found in this study (Index 1 = 62.8 kg per cow, Index 2 =
1 5
28.3 kg per 100 kg cow LW and index 3 = 120.8 kg per 100 kg metabolic LW) are in
1 6
agreement with productivity indices found in Ndama cattle under once-daily milking system in
1 7
The Gambia where index 1, 2 and 3 averaged 60.4, 28.3 and 120.2 kg (Agyemang et al.,
1 8
1991). Village Ndama cow productivity seems relatively lower than that found in Ndama cows
1 9
reared on station with no milk extraction. Productivity indices 1, 2 and 3 were 70.1, 29.1 and
20
127.0, respectively for Ndama cows reared on station in Senegal (Fall et al, 1983).
2 1
22
Acknowledgements
2 3
This work was jointly carried out by ISRA, ILCA and ILRAD and was supported by the
24
European Development Fund. Additional fund provided by the British Overseas Development
2 5
Administration (ODA) allowed the main author to spend time at the Centre for Tropical
26
Veterinary Medicine, University of Edinburgh to analyse and publish the data. Comments
2 7
fi-om A.S. Peregrine are greatly appreciated.
2 8
29
30
References
3 1
Agyemang, K., Dwinger, R.H. Grieve, A.S. and Bah, M.L., 1991. Milk production
3 2
characteristics and productivity of N’Dama cattle kept under village management in The
3 3
Gambia. Journal of Dairy Science, 74, 1559-1608
34
3 5
Agyemang, K., Dwinger, R.H. Jeannin, P., Leperre,P. Grieve,A.S. Bah, M.L. and Little, D.A.,
3 6
1990. Biological and economic impact of trypanosome infections on milk production in
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Ndama cattle managed under village conditions in The Gambia. Animal Production, 50: 383-
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389
39
40
Agyemang,K., Little, D.A. Mattioli, R., Sonko, E. and Janneh, L., 1993. Effects of
4 1
trypanosome infection and postpartum liveweight change on resumption of reproductive
42
activity in N’dama CO~S. Theriogenelogy, 39:985-995
4 3
44
Challier, A. et Laveissière, C., 1973. Un niveau piège pour la capture de glossines, description
4 5
et essais sur le terrain. Cah. Orstom Ser. Ent. med. Parasitol., no 11: 25 l-262
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47
Claxton, J.R. Leperre, P., Rawlings, P., Snow:, W.F. and Dwinger, R.H., 1992.
48
Trypanosomiasis in the Gambia: Incidence, prevalence and tsetse challenge, Acta Tropica, 50,
49
219-225.
5 0
1 0
Dwinger, R.H., Agyemang, K., Kaufmann, J., Grieve, A.S. and Bah, M.L. 1994. Effects of
2
trypanosome and helminth infections on health and production parameters of village N’Dama
3
cattle in The Gambia. Veterinary Parasitology, 54,353-365
4
5
Fall, A., Diop, M., Sandford, J., Wissocq, Y.J. Durkin, J. and Trail, J.C.M., 1983.
6
Productivities of Djallonke Sheep and Ndama Cattle at the Centre de Recherches
7
Zootechniques at Kolda, Senegal. ILCA Research Report no. 3. ILCA, Addis Ababa,
8
Ethiopia.
9
10
Jackson, C.H.N., 1946. An artificially isolated generation of tsetse flies (Diptera). Bulletin of
11
Entomological Research, 37 :29 l-299
1 2
1 3
Kaufmann, J. and Pfister, K., 1990. The seasonal epidemiology of gastrointestinal nematodes
1 4
in N’Dama cattle in The Gambia. Veterinary Parasitology, 37,45-54
1 5
1 6
Leak, S.G.A., Woudyalew Mulatu, Authié, E., d’iteren, G.D.M., and Peregrine, A.S.,
1 7
Rowlands, G.J. and Trial, J.C.M., 1993. Epidemiology of bovine trypanosomiasis in the
1 8
Ghibe valley, Southwest Ethiopia. 1. Tsetse challenge and its relationship to trypanosome
1 9
prevalence in cattle. Acta Tropica, 53, 12 1- 134
20
21
Little, D.A., Wassinls, G-J., Agyemang, K., Leperre, P., Janneh, L. and Badje, B., 1994. Feed
22
supplementation of lactating N’Dama cows under village husbandry. Tropical Agriculture
23
(Trinidad), 71,223-228
24
25
Murray, M., 1988. Trypanotolerance, its criteria and genetic and environmental influences. In
26
Livestock Production in Tsetse Affected Areas of AfricA. Proceedings of a meeting held 23-27
27
November 1987, Nairobi, Kenya. International Livestock Centre for Afiica (ILCA)/
28
International Laboratory for Research on Animal Diseases (ILRAD).
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30
Murray, M., Trail, J.C.M., Turner, D.A. and Wissocq,Y., 1983. Livestock Productivity and
31
Trypanosomiasis. Network Training Manual. International Livestock Centre for Afiica. Addis
32
Ababa, Ethiopia.
33
34
Rowlands, G.J., Woudyalew Mulatu, Authié, E., d’ieteren, G.D.M., Leak, S.G.A., Nagda,
35
S.M. and Peregrine, A.S., 1993. Epidemiology of bovine trypanosomiasis in the Ghibe valley,
36
Southwest Ethiopia. 2. Factors associated with variations in trypanosome prevalence,
37
incidence of new infection and prevalence of recurrent infections. Acta Tropica, 53, 135-150
38
39
Sanyang, F.B., Wagner, H.-G.R. and Clifford, D.J., 1995. Influence of suckling on calving
40
interval of Ndama cows in The Gambia. Tropical Animal Health and Production, 27: 191-l 92
41
42
SAS Institute Inc., 1989, SASSTAT User’s Guide, Version 6, Fourth Edition, Volume 2,
43
Cary, NC: SAS Institute Inc., 1989. 846pp
44
45
Stephen, L.E., 1986. Trvpanosomiasis, a veterinarv perspective. Pergamon Press. Oxford,
46
England.
47
48
Thorpe, W., Coulibaly, L., Defly, A., d’Ieteren, G.D.M., Feron, A. Grundler, G. Hecker, P,
49
Itty, P., Maehf, J.H.H., Mawuena, K., Morkramer, G., Mulungo, M., Nagda, S.M., Paling,
50
R.W., Pelo, M., Rarieya, J.M., Shuetterle, A. and Trail, J.C.M., 1988. Facterus influençant les
5 1
performances de reproduction dans diverses situations du réseau. In Production Animale dans
t
11
1
les R&ions d’Afrique Infestées par les Glossines. Compte rendu réunion, 23-27 Novembre
2
1987, Nairobi, Kenya. Centre International pour 1’Elevage (CIPEA).
Table 1. Number of flies caught, number of flies dissected , unadjusted mean (*SD) yearly
number of Glossina morsitans submorsitans and Glossina nalnalis gambiensis caught per trap
per day, flies infection rates by Trypanosoma congonlense and Trvnanosoma vivax, and tsetse
challenge index (tsetse infection x number of flies caught per trap per day) at Kolda fi-om
march 1988 to march 1992.
~---
No.
No. flies
FTD’
FIR2
TC13
months cawht
dissected
Year
1988 10
2528
1546
6.1
2.1
21.1
1989 12
3968
2120
8.4
1.7
18.2
1990 11
2879
1121
6.4
4.8
33.7
1991 12
835
292
1.9
1.0
0.9
1992 3
84
29
0.8
2.8
0.1
7
8
1: FTD: Fly per trap per day; 2: FIR: Fly infection rates; 3: TCI: tsetse challenge index
1 3
1
Table 2.
Least square means infection rates with Trypanosoma congodense and
2
Trypanosoma vivax and packed ce11 volume (PCV %) in Ndama cattle kept under village
3
m
between 1999 and 1992.
-_x---m*
Source of variation
Trypanosome infection
Packed ce11 volume (%)
rate(%)
rl
mean f s.e.m
--IIxII.~-_--_l-..
n
mean f s.e.m
e...-----
Overall mean
9905
2.5 f 0.51
5972
27.7 If: 0.27
-
Year: ***
1988
259
1.4 f 1.2
210
30.5 f 0.43
1989
1458
2.4 f 0.6
1014
29.1 f 0.29
1990
1137
3.2 f 0.7
792
26.2 f 0.31
1991
3396
3.1 f 0.5
2151
26.4 f 0.27
1992
3655
2.4 f 0.6
1805
26.1 f 0.28
Sex ***
Female
6772
2.8 f 0.3
3589
27.5 f 0.23
Entire male
2968
3.4 f 0.4
2286
26.4 f 0.23
Castrated male
165
1.3 f 0.3
97
29.1 jz 0.23
Age ***
< 1 year
1586
1.9 f 0.7
1327
27.9 A 0.29
l-3 year
3398
1.9 * 0.5
2741
27.4 f 0.29
> 3 year
4921
3.6 * 0.5
1904
27.7 f 0.27
Strongyle infection (P= 0.08)
Negative
4127
28.0 f 0.29
Positive
1889
27.3 f 0.38
Trypanosome infection * **
Negative
5866
29.3 f 0.18
Positive
150
26.0 f 0.44
Tryp. x Strongyle infection
Negative
Negative
4025
29.7 f 0.19
Negative
Positive
1841
28.9 f 0.19
Positive
Negative
102
26.4 -f 0.48
Positive
Positive
4 8
25.7 f 0.69
4
Significance levels : *** P<O.Ol
14
1
Figure 1. Monthly tsetse challenge index and cattle infection rates with T. congonlense and T.
2
vivax
3
4
/----
45
40
35
J
F
M
A
M
J
J
A
S
O
N
D
5
/--
-
6
7
8
9
Figure 2. Mean monthly strongyle prevalence and egg output in Ndama cattle
1 0
600
Ê
E. 500
6 0
=
2
$j
5 0
400
L
ô
Y
2
40 fj
2 300
E
i!
3 0 8
g)
0.
200
8,
2 0
P
P 1 0 0
W
1 0
0
J F M A M J J A S
01 N D
Month
11
1 5
1
2
Figure 3. Monthly packed ce11 volume (PCV, %) and trypanosome prevalence in village
3
Ndama cattle between 1988 to 1992.
4
3 0
‘
,
’
I
\\-
I
I
I
,
I
.
I
2 6
J
F M A M J
J A S 0 N D
Month
5
1 6