Livestock keeper perceptions of four indigenous cattle breeds in tsetse infested areas of Ethiopia

Four cattle breeds indigenous to western and south-western Ethiopia - Abigar, Gurage, Horro and Sheko - were included in a study of the perceptions of smallholder cattle keepers regarding cattle management, production levels and constraints for production. A semi-structured questionnaire was used and 60 cattle keepers from each of the four areas were interviewed. Diseases were reported as the main constraint to cattle production by a majority of livestock keepers in all areas except in the Sheko area, where over-stocking was the main constraint. Among diseases, trypanosomosis was the main livestock disease according to more than half of Gurage, Horro and Sheko keepers, whereas anthrax was most important in the Abigar area. Gurage had highest age at first calving, longest calving interval and also the lowest milk production, whereas Sheko and Abigar had the most favorable characteristics both for milk production (600–700 kg) and fertility (age at first mating 3–3.5 years and above 8 calves/cow). Cattle keepers in the Sheko area reported relatively less problems with cattle diseases compared to the other areas, especially regarding trypanosomosis. Abigar showed a different disease pattern than the other breeds and may also have advantages as regards trypanotolerance.     

Response of four indigenous cattle breeds to natural tsetse and trypanosomosis challenge in the Ghibe valley of Ethiopia

A comparative study on the response of four indigenous cattle breeds of Ethiopia, namely Abigar, Horro, Sheko and Gurage, to natural challenge of trypanosomosis in the Tolley-Gullele area of the Ghibe valley has been undertaken from August 2000 until August 2004. Fifty female yearlings each of Horro, Sheko and Abigar and 31 of the Gurage were purchased from their natural habitats and introduced in to medium to high tsetse-trypanosomosis challenge area of the Ghibe valley. While the natural habitats of first three breeds are naturally infested with tsetse flies and trypanosomosis, that of the Gurage is known to be very minimal, if any, and hence the Gurage breed was used in this study as the known susceptible breed. During the study animal health, production performance and tsetse fly situation were monitored monthly. The Sheko breed has manifested very significantly (p<0.001) high overall average packed cell volume (PCV) values (25%) compared to that of Abigar (24%), Horro (23%) and Gurage (22%). It also had the lowest mean trypanosome prevalence rate of 9% against 23% of Horro, 26% of Abigar and 27% of Gurage, and the least number of Berenil treatments (1.36) compared to Abigar (4.0), Horro (4.6) and Gurage (6.7). While the Abigar manifested high sensitivity and frequent death to PCV depression, the Horro showed strong resilience to PCV depression and better response to Berenil treatment assistance. At this stage the Sheko breed was also found to be equal to the other breeds in its reproductive performance. These results need to be substantiated with further in-depth investigation including immune response, animal behavior and environmental influences.     

Breed and trait preferences of Sheko cattle keepers in southwestern Ethiopia

Like their smallholder subsistence counterparts in developing countries, breed and trait preferences of Sheko cattle keepers have broad perspectives. Our study has documented breed and trait preferences of Sheko cattle keepers in southwestern Ethiopia—the natural breeding tract of Sheko cattle. Our results showed that due to their multifunctionality, cattle are the most preferred livestock species. Overall, farmers showed slightly more preference to local Zebus over Sheko breed. This is due to voracious feeding behavior of Sheko cattle, which make them less preferable in the face of worsening feed shortage, and due to aggressive temperament of Sheko cattle. This is despite Sheko's outperforming potential over local Zebus in their milk production, draft power, and hardiness. At trait level, overall milk production was consistently reported as the most preferred trait followed by fertility and traction. This trait preference rank has matched with the reported frequency count ranks for Sheko cattle use. However, breed preference rank has not matched with reported trait preference ranks because Sheko excels local Zebus in all the three most preferred traits, but it was ranked second. Therefore, to minimize these conflicting interests, breed management plans for Sheko cattle should target on strategies that help to solve feed shortage problem and to improve feeding practices, and on selection of less aggressive Sheko cattle. Therefore, these strategies should be considered in line with Sheko cattle conservation and genetic improvement programs.     

The performance of Orma Boran and Maasai Zebu crossbreeds in a trypanosomosis endemic area of Nguruman, south western Kenya

Studies on the trypanotolerance of Orma Boran X Maasai Zebu (Orma Zebu) crossbred cattle (F1 progeny) and pure-bred Maasai Zebu contemporaries were carried out in Nguruman, south western Kenya. The two groups were monitored from birth for a period of 2 years. The incidence of trypanosomosis, parasitaemia, packed cell volume (PCV), body mass and average daily mass gain were monitored. During the study period, overall trypanosomosis incidence was low (3%). The crossbred cattle had a higher incidence of infection (61% vs 39%). The mean PCV and mean mass gain for the crossbred cattle was higher than that of the Maasai Zebu. The mean calf body mass at weaning (8 months) for the Orma Zebu and Maasai Zebu was 72 kg and 64 kg, respectively, while at 18 months of age their mean body mass was 164 kg and 123 kg, respectively. During the rainy season significant differences in average daily mass gains were noted (P < 0.05). The superior mass gain of the Orma Zebu observed during the rainy season, despite higher infection rates, indicate an enhanced trypanotolerance. Moreover, the better performance of the Orma Zebu is an attribute that could be exploited in the adoption of the trypanotolerance genotype, as a sustainable trypanosomosis control strategy.     

Trypanosomosis: a priority disease in tsetse-challenged areas of Burkina Faso

Trypanosomosis is an important disease affecting humans as well as animals. It remains a big constraint to livestock productions in tropical areas. The objective of this study was to assess the importance of trypanosomosis among cattle diseases in Burkina Faso, mainly in tsetse-challenged areas, and to capture information on how farmers apply available methods for controlling the disease. A survey has been carried out in 29 villages of Burkina Faso in three regions (north, southwest, and west regions). One hundred and thirty-four cattle breeders were interviewed individually with a questionnaire. The results indicate that among the 16 diseases mentioned by cattle breeders, trypanosomosis is the most important one in tsetse-challenged areas. Overall, 76.12 % of the breeders mentioned it as the most important disease, while 54.55 % of the farmers in the southwest region and 70.91 % of the farmers in the west region ranked it as a priority disease. Chemoprophylaxis/chemotherapy is widely used as a control method. Isometamidium chloride and diminazene aceturate were used by 53.49 and 46.52 % of the responders, respectively. Among farmers, 85.55 % ranked diminazene aceturate as the less efficient while 14.45 % ranked isometamidium chloride as the most efficient trypanocid. Trypanocidal drug quality and drug resistance were raised as a major concern by 30.77 and 50 % of the respondents, respectively. According to them, zebu cattle are more susceptible to trypanosomosis than taurine Baoule cattle and their crosses with zebu, emphasizing that crossing susceptible breeds with trypanotolerant ones, could be used as part of an integrated control strategy.     

Identification of mechanisms of natural resistance to African trypanosomiasis in cattle

Natural resistance to African trypanosomiasis in certain Bos taurus cattle in West Africa, called trypanotolerance, may hold solutions for control of this economically crippling disease. Comparison of immune responses between trypanotolerant and trypanosusceptible cattle have shown some differences in antibody response, complement level and cytokine expression, but it is not known whether these differences are the cause of resistance.Two experiments were carried out to assess the contribution of the immune and haemopoietic systems to trypanotolerance. The production of haemopoietic chimaeras from trypanotolerant and susceptible twin calves and comparison of their responses after infection with singleton calves, allowed an assessment of the role of the haemopoietic system in trypanotolerance. An in vivo depletion of CD4 cells in the two breeds allowed an appraisal of the role of T and B lymphocytes in trypanotolerance. The results of the two experiments suggest that natural resistance comprises at least two mechanisms, an innate mechanism that controls parasite growth, and another, involving the haemopoietic system, that is able to limit anaemia. This supports the hypothesis that innate mechanisms in trypanotolerant cattle are more efficient in controlling disease, making them less reliant on antibody responses.     

The area-wide epidemiology of bovine trypanosomosis and its impact on mixed farming in subhumid West Africa; a case study in Togo.

This paper reports on an area wide study of all major variables determining the expression of trypanosomosis in cattle in the subhumid eco-zone of West Africa, taking Togo as an example. To enable systematic area-wide sampling, the country was divided in 311 grid-squares of 0.125 x 0.125 sides. Cross-sectional surveys were then conducted to generate maps or digital layers on cattle density, herd structure, ownership and breed. These data layers, except for the breed data, were subjected to a cluster analysis in order to define spatial patterns in animal husbandry systems. This analysis revealed two main systems: one is oriented towards integration with crop-agriculture and a second towards investment in cattle. These two systems could be further characterised by incorporating breed data. Zebu cattle and their crossbreeds are more favoured in the second system. The breed distribution map shows the actual situation but also serves to predict the outcome of progressive crossbreeding. An area wide trypanosomosis survey allowed the production of prevalence maps for Trypanosoma congolense, T. vivax and the associated packed cell volume (PCV) values. A simple curvi-linear relationship was established between vector density and disease prevalence. The regression between disease prevalence and PCV for taurine and zebu plus crossbreeds separately, revealed that taurine cattle maintain a comparatively high PCV level particularly in high prevalence scenarios. The relationship between the average herd PCV and cattle density suggests that herd PCV value may provide a mirror for the number of animals not kept because of the prevailing risk. The regression between agricultural intensity and cattle density subsequently in areas with decreasing herd PCV values reveals that the level of integration of cattle in crop production decreases with a decreasing PCV. Thus, despite the presence of taurine animals in Togo, the omnipresence of tsetse in particular Glossina tachinoides, remains a major obstacle to cattle raising and indirectly mixed farming development and intensification. It is argued that only with the present type of wide scale, spatial studies it becomes possible to clarify all the major variables influencing the expression of trypanosomosis. Spatial epidemiological studies at a macro level may form the basis for area wide trypanosomosis control in West Africa.     

Responses of bovine chimaeras combining trypanosomosis resistant and susceptible genotypes to experimental infection with Trypanosoma congolense

West African N'Dama cattle have developed a genetic capacity to survive, reproduce and remain productive under trypanosomosis risk. The cellular and molecular bases of this so-called trypanotolerance are not known, but the trait is manifested by the N'Dama's greater capacity to control parasitaemia and anaemia development during an infection. In order to examine the role of the haematopoietic system in trypanotolerance, we have exploited the tendency for the placentas of bovine twin embryos to fuse. Placental fusion in cattle results in bone marrow chimaerism in twins. By comparison with the N'Dama, cattle of the East African Boran breed are relatively susceptible. We evaluated the role of the haemopoietic system in trypanotolerance by comparing the performance of five Chimaeric Boran/N'Dama twin calves with that of singletons of the two breeds. Chimaeric Boran/N'Dama pairs of twins were produced in recipient Boran cows by embryo transfer, and the majority of haemopoietic cells in all twinned individuals were of Boran origin. Thus, N'Dama chimaeras differed from N'Dama singletons in that the bulk of their haemopoietic system was derived from their susceptible Boran twins, while Boran chimaeras differed little from Boran control animals. All cattle became parasitaemic and developed anaemia. The N'Dama chimaeras did not manage their anaemia and white blood cell counts effectively. However, they were able to limit parasitaemia development. These results suggest that trypanotolerance is the result of two mechanisms, one that improves parasite control and is independent of the genetic origin of the haemopoietic tissue, and another that is influenced by haemopoietic tissue genotype and which improves control over anaemia. The capacity to maintain growth during infection was similarly dependent on the genetic origin of the haemopoietic tissue.     

Growth and Mortality in Sheep and Goats under High Tsetse Challenge in Kenya

Trypanosomosis is a major impediment to livestock production and economic development in those areas of Africa where it is endemic. Although small ruminants appear to perform better than cattle in various agro-ecological zones, the importance of trypanosomosis has not been extensively investigated in these livestock. This study was designed to investigate the prevalence of trypanosomosis in sheep and goats in an endemic area and to evaluate the performance of different breeds under high tsetse challenge and the potential role of chemoprophylaxis in the control of the disease. The results showed that tsetse flies feed readily on small ruminants, and that these animals are susceptible to trypanosomosis. The Small East African goats acquired fewer infections than the Black Head Persian and Dorper sheep used in the study. In both sheep and goats, chemoprophylaxis with isometamidium chloride (Samorin, Rhone Merieux, Annecy, France) was protective, resulting in fewer infections and higher body weight gain. Trypanosomosis caused anaemia in both sheep and goats, and animals whose PCV fell below 15% rarely recovered, even with trypanocidal drug treatment. The peak transmission period was between 1 and 3 months after the peak tsetse fly density, which raises the possibility of effective strategic prophylaxis.     

Mapping the economic benefits to livestock keepers from intervening against bovine trypanosomosis in Eastern Africa

Endemic animal diseases such as tsetse-transmitted trypanosomosis are a constant drain on the financial resources of African livestock keepers and on the productivity of their livestock. Knowing where the potential benefits of removing animal trypanosomosis are distributed geographically would provide crucial evidence for prioritising and targeting cost-effective interventions as well as a powerful tool for advocacy. To this end, a study was conducted on six tsetse-infested countries in Eastern Africa: Ethiopia, Kenya, Somalia, South Sudan, Sudan and Uganda. First, a map of cattle production systems was generated, with particular attention to the presence of draught and dairy animals. Second, herd models for each production system were developed for two scenarios: with or without trypanosomosis. The herd models were based on publications and reports on cattle productivity (fertility, mortality, yields, sales), from which the income from, and growth of cattle populations were estimated over a twenty-year period. Third, a step-wise spatial expansion model was used to estimate how cattle populations might migrate to new areas when maximum stocking rates are exceeded. Last, differences in income between the two scenarios were mapped, thus providing a measure of the maximum benefits that could be obtained from intervening against tsetse and trypanosomosis. For this information to be readily mappable, benefits were calculated per bovine and converted to US$ per square kilometre. Results indicate that the potential benefits from dealing with trypanosomosis in Eastern Africa are both very high and geographically highly variable. The estimated total maximum benefit to livestock keepers for the whole of the study area amounts to nearly US$ 2.5 billion, discounted at 10% over twenty years – an average of approximately US$ 3300 per square kilometre of tsetse-infested area – but with great regional variation from less than US$ 500 per square kilometre to well over US$ 10,000. The greatest potential benefits accrue to Ethiopia, because of its very high livestock densities and the importance of animal traction, but also to parts of Kenya and Uganda. In general, the highest benefit levels occur on the fringes of the tsetse infestations. The implications of the models’ assumptions and generalisations are discussed.     

Farmers’ perceptions on trypanosomosis and trypanotolerance character of the taurine Sheko

In the humid and subhumid tropics, trypanosomosis is an economically important zoonotic protozoan disease of the commonly kept farm animal species and their wild relatives. For example, more than 20% of the humid western and southwestern Ethiopia, which is home to more than 14 million heads of cattle, is under varying levels of trypanosomosis risk. Our study was, therefore, initiated to document farmers’ perception on trypanosomosis and Sheko’s trypanotolerance character. Our findings showed that trypanosomosis was the most frequently reported cattle disease in the Bench Maji Zone. Accordingly, 76.7% of the farmers reported the epidemiological importance of trypanosomosis, and they also noted that trypanosomosis on average accounted for 63.0% of annualized cattle death. The reported signs of trypanosomosis and trypanotolerance indicators were consistent with literature reports. Moreover, 66.7% of the farmers reported Sheko’s trypanotolerance character. In the course of time, smallholder farmers have developed ethnoveterinary practices that are mainly used to prevent the landing of vector flies on the animal. Wet and warm seasons of the year, i.e., spring and, to some extent, the beginning of summer and autumn, were reported as peak periods of trypanosomosis risk. Therefore, this showed the need for incorporating farmers’ knowledge in trypanosomosis control programs.     

Serum haemolytic complement activity and C3 levels in bovine trypanosomosis under natural conditions of challenge--early indications of individual susceptibility to disease

Twenty-five Baoule (Bos taurus) and 12 Zebu (Bos indicus) cattle, which were part of an experiment aimed at characterizing cattle for resistance to trypanosomosis under natural challenge in Burkina Faso, were monitored for complement levels. Total haemolytic activity of the alternative complement pathway and C3 in sera taken weekly were estimated. The results were analysed in relation to the course of the disease, parasitological data, packed red cell volume (PCV) and body weight. All the animals became infected with Trypanosoma vivax and/or T. congolense. The Zebu had to be treated with Berenil (Diminazene aceturate, Hoechst, W. Germany) after a mean period of 5 weeks of infection, whereas 7 of the 25 Baoule remained in good condition throughout the experiment. The remaining 18 Baoule required treatment after a variable period of infection. There was a decrease in haemolytic complement activity (HC') as well as in C3 levels, which coincided with the first detection of parasites in the blood. The titres in the Zebu fell to 10-20% of pre-infection level within 2-3 weeks and they showed no tendency towards regaining normal levels. The drop in complement in the Baoule was less pronounced and was in most cases followed by an increase approaching normal values. In these animals, the complement level in early infection was found to depend on the intensity of parasite load and on the control potential of each individual. There was a significant correlation between minimum complement activity (min. HC'), minimum C3 (min C3) and minimum PCV (min.PCV) in early infection. These three parameters correlated with individual resistance and might, therefore, be useful criteria for the identification of the most resistant individuals within a trypanotolerant breed.     

Production Objectives and Management Strategies of Livestock Keepers in South-East Kenya: Implications for a Breeding Programme

A survey of pastoralist and agropastoralist households in south-east Kenya was conducted to determine their production objectives and management strategies in order to optimize and extend a breeding programme for indigenous small East African Shorthorn Zebu cattle. The reasons for keeping cattle and the breed/trait preferences identified reflect the multiple objectives of the livestock keepers, with both adaptive traits and productive/reproductive traits rated as important. Although the Maasai and Kamba zebu (M&KZ) breeds were ranked highly with regard to adaptive traits, the population is considered to have been in decline over recent years. In order to promote the conservation and sustainable use of the M&KZ cattle, the formation of an open nucleus breeding scheme is recommended. In particular, such a scheme would be able to address several existing constraints (e.g. individual herds are very small and communal use of pastures/water makes controlled mating difficult). Such interventions would require the full participation of the livestock keepers, as well as ensuring that a holistic approach to species and breed attributes is taken into account in setting breeding goals, such that the full array of contributions that livestock make to livelihoods and the genetic characteristics related to these contributions are fully incorporated into the programme.     

A survival analysis of trypanosomosis diagnostic-test performance under natural infection challenge

Little is known about the time-to-first detection and the time difference (TD) between first parasitological and first serological diagnosis of Trypanosoma spp. infections under natural infection challenge in cattle. The objective of our study was to estimate these measures of "longitudinal aspects" of diagnostic performance and to investigate potential biological factors. Emphasis was on diagnosis at the genus level (Trypanosoma spp.). Twelve N'Dama, 12 Gobra zebu and 12N'DamaxGobra (F1) crossbred cattle (all animals non-infected at the start of the experiment, six male and six female animals in each cohort) were exposed to natural high tsetse challenge in the Niamina East area in The Gambia [Acta Trop. 71 (1998) 57]. The animals were investigated parasitologically (detection of trypanosomes by buffy-coat technique), serologically (detection of T. brucei, T. congolense and T. vivax antigen by enzyme-linked immunosorbent assay (ELISA)) and clinically (packed-cell volume, PCV) over a period of 180 days. The time-to-first detection of trypanosomes, trypanosomal antigen (cut-off as suggested by test supplier) and drop in PCV (subject-based cut-off values) were recorded as outcomes of interest. Thus, incidence was both parasitologically (I(p)), serologically (I(s)) and clinically (I(c)). Recurrent events were not considered. The TD between first parasitological and first serological detection was established as I(s) time minus I(p) time. The effect of breed and sex on the time-to-first detection and on TD was investigated using Cox (proportional hazard) regression and ANOVA, respectively.We found that time-to-first parasitological detection of trypanosomosis in N'Dama animals was significantly longer than in the two other breeds (Cox regression, P=0.002). A similar but less-strong (P=0.063) effect of breed on time-to-first detection of trypanosomal antigen was found, whereas no breed effect was observed for clinical detection (P=0.432). Sex had no effect in all detection systems. The TD varied between -56 and 115 (mean 28). Marked differences among breeds and between sexes were not observed (ANOVA, P=0.8). We suggest that incidence studies are more suitable for detecting risk factors for animal trypanosomosis than prevalence-based (cross-sectional) studies because the latter often result in misinterpretation of factors that increase the survival time with infection as risk factors.     

Parasitological prevalence of bovine trypanosomosis in Kindo Koisha district,Wollaita zone,south Ethiopia

A cross sectional survey to determine the distribution and prevalence of trypanosomosis was conducted in Kindo Koisha district, in the Wollaita zone in southern Ethiopia. A total of 1 008 adult cattle was examined at eight different localities. Dark field examination of the buffy coat, as well as stained thin blood film examination and packed cell volume (PCV) evaluation were the diagnostic techniques used. The overall prevalence of bovine trypanosomosis was 15 %. Among the positive animals, 108 (71.1%), 43 (28.4%) and 1 (0.6%) were due to Trypanosoma vivax, Trypanosoma congolense and mixed infection (T. vivax and T. congolense), respectively. The infection rate of T. vivax and T. congolense varied significantly (P < 0.01). The mean PCV of the positive and negative animals ranged between 18.3-32.1% and 26.8-33.4%, respectively. The mean PCV of negative animals (28 %) was significantly higher than the mean PCV of positive animals (22.3%) (P < 0.001). There was an inverse association of PCV with the prevalence of trypanosomosis (P > 0.05). The herd average PCV values of each site decreased with increasing proportion of the positive herds of that particular site. Of the diagnostic tests employed, the microhaematocrit buffy coat technique is relatively sensitive and it has an added advantage of indicating the general condition of the animal by haematocrit measurement. In view of the risk of trypanosomosis, a control intervention through the strategic application of appropriate trypanocidal drugs is recommended. A tsetse fly control scheme to reduce host-tsetse fly contact is equally as important as chemotherapy and chemoprophylaxis against trypanosomosis.     

Bovine trypanosomosis in the Bolivian Pantanal

Trypanosomosis caused by Trypanosoma vivax has been a constraint for cattle production in the Bolivian lowlands, since it was introduced in 1996. Flooded areas like the Bolivian Pantanal have a suitable environment for the presence and transmission of Salivarian trypanosomes and farmers from that region often report trypanosomosis-like problems on their farms. The objective of the present study, therefore, was to characterize the epidemiology of bovine trypanosomosis in the Bolivian Pantanal. In order to achieve this objective, 202 cattle from the province of Angel Sandoval and 209 cattle from the province of German Busch were randomly sampled (the Pantanal is located in both provinces). Twenty-nine farms in both provinces were visited, the farmers interviewed, and biologic samples collected from their cattle. Samples were submitted for parasitological and PCR evaluation and the prevalence of bovine trypanosomosis was estimated for each province. Laboratory results were correlated with the sampled animals packed cell volume (PCV) and body condition (BC) scores and the observed T. vivax parasites measured for morphometry analysis. Results from this study show differences in morphometric measures between T. vivax parasites from each province. Differences between provinces were also observed in the T. vivax-related disease situation. While in Angel Sandoval the PCV and BC of T. vivax-affected animals were significantly lower than those of the T. vivax-negative animals, in German Busch no differences were observed in the PCV and BC of T. vivax-positive or negative animals. Animal prevalence of T. vivax in Angel Sandoval was 27.79% (95% CI: 14.52-44.28) and in German Busch was 19.03% (95% CI: 9.19-30.75). The T. evansi animal prevalence in each province was 0.99% (95% CI: 0.27-2.99) and 5.71% (95% CI: 2.43-12.19), respectively. Based on questionnaire and laboratory results, it was concluded that trypanosomosis is a primary constraint for cattle production in the Bolivian Pantanal.     

Survey of bovine trypanosomosis in the Kachia Grazing Reserve,Kaduna State,Nigeria

This study assessed the prevalence of trypanosomes in cattle at the Kachia Grazing Reserve (KGR) in March and June 2004 and in February 2005. A total of 1293 cattle blood samples were collected at random. The samples were analysed using the buffy coat technique and Giemsa thin blood films for parasite detection and identification. The effects of herd pen location to watering and grazing point's distances (using the global positioning system (GPS)) were determined and mean Packed cell volume (PCV) assessed. Overall, the detected prevalence of trypanosomosis was 8.4%, much higher than the previous prevalence of 5.3% before the present study was conducted. The prevalences in the months of March, June (2004) and February (2005) were 2.3%, 11.6% and 15.4%, respectively. Increased prevalence was associated with proximity of herd pens to watering point's distances (χ² for linear trend = 4.447, P < 0.05), but no association of herd pens to grazing point distances (χ² = 2.186, P > 0.05); suggesting that hydrological network played an important part in trypanosomosis transmission. The mean PCV of parasitaemic and apparasitaemic cattle were respectively 25.99 ± 1.82% and 29.31 ± 1.70%. The drop in mean PCV was most in 0–1-year age group, 23.47 ± 3.10% and was statistically significant (P < 0.05), suggesting that anaemia was most pronounced in this age group. Factors that may have contributed to the increased prevalence obtained were collapse of control measures and breed susceptibility. Since, Zebu cattle were the predominant breeds in the reserve, the study advocates effective use of insecticide impregnated screens (traps and targets) with community participation in mind for sustainability. If government intervenes through PATTEC ground spraying of insecticides in the reserve is recommended. In addition, chemotherapeutic and chemoprophylaxis should be systematically used to fight the problem of trypanosomosis in the KGR towards improved livestock production.     

Health and productivity of traditionally managed Djallonke sheep and West African dwarf goats under high and moderate trypanosomosis risk.

Trypanosome infections, packed red cell volume levels (PCV), body weight and nematode faecal egg counts of village-based small ruminants were monitored in two areas in The Gambia with either moderate or high trypanosomosis risk for 24 and 30 months respectively. Outflows from the flock and new-born animals were recorded and data on housing and management were compiled. Reported mortality rates were higher in goats than in sheep, but for both species highest in the moderate risk area. The peak of trypanosome infections lagged the peak of tsetse densities by 1-3 months in both areas. Trypanosoma vivax was the predominant species found in the infected animals, followed by T. congolense. Trypanosome prevalence was, in general, higher in sheep than in goats but only significantly higher during Year 1 in the moderate risk area. Trypanosome infection reduced the PCV level significantly and seasonal effects indicated significantly lower PCV levels during the rains. Trypanosome infection significantly depressed weight gain in both species at periods where infection rates were highest. In both species considerably lower weight gains were observed during the rainy season. Abortion rates were higher in goats than in sheep in both study sites, and highest in the high-risk site. Trypanosome infection in ewes in the high risk area increased lamb mortality significantly but had no effect on birth weights, nor on growth rates up to 4 months. Offspring mortality up to 4 months was generally high at both sites. Trypanosome infection in the dam between 3.5 to 7 months post parturition significantly increased parturition interval in both species. Peak faecal egg output occurred at the end of the rainy season and was highest for both species in the moderate risk site. Poor grazing management was found responsible for a seasonal nutritional constraint. Based on these results, these breeds of sheep and goats can be considered as trypanotolerant since they are able to remain productive under high and moderate levels of trypanosome challenge. Nevertheless, trypanosomosis affected their health and production level as shown by reduced PCV levels, depressed weight gains, longer parturition intervals and higher lamb mortality. In addition, during the rains, helminth infections and poor management leading to nutritional constraints had also a negative impact on health and production and therefore influenced the innate resilience to trypanosomosis in those indigenous breeds. Adaptations in management may have an equal impact as certain disease control measures to improve biological and economical returns from small ruminants in tsetse infested rural areas.     

Relationships between trypanosome infection measured by antigen detection enzyme immunoassays, anaemia and growth in trypanotolerant N'Dama cattle.

Relationships were evaluated between trypanosome infection as measured by antigen detection enzyme immunoassays (antigen ELISA), anaemia as determined by average packed red cell volume (PCV), and animal performance as assessed by daily weight gain in 99 N'Dama cattle in Gabon exposed to natural tsetse challenge at 11.5 months of age and recorded 14 times over a 13 week period. Approximately half the animals were found to be infected for an average of five of the 14 times that they were examined: 38% with Trypanosoma congolense, 13% with Trypanosoma vivax and 49% with a mixed infection. Trypanosoma congolense infections had significant deleterious effects on animal growth, while T. vivax infections did not. Animals found on several occasions to be infected with T. congolense had significantly lower PCV values than those demonstrated to be infected on fewer occasions. No relationship was found between mean optical density (OD) values in antigen ELISA and PCV values. Animals capable of maintaining PCV values, even when antigen ELISA positive on a high number of occasions, grew at the same rate as uninfected animals. Animals that could not maintain PCV values when infected had poorer growth. Antigen ELISA has the potential to increase the efficiency of selection of trypanotolerant N'Dama cattle under tsetse challenge in the field, in three main ways. (1) Accurate identification of trypanosome species, especially in mixed species infections, clarifies relations between infection, anaemia and animal performance. (2) Detection of animals antigenaemic without patent parasitaemia could allow individuals with superior ability to control trypanosome infection to be identified. (3) More accurate measurement of the proportion of time an animal is infected allows more accurate evaluation of its anaemia control capability.     

Susceptibility of N'Dama cattle to experimental challenge and cross-species superchallenges with bloodstream forms of Trypanosoma congolense and T. vivax.

Susceptibility to Trypanosoma congolense, T. vivax challenge and cross species-superchallenges, and related effects on health and productivity were assessed in N'Dama cattle. Twenty-five N'Dama bulls aged 3-4 years and previously primed with trypanosome infections through natural tsetse exposure over more than one year were used. The experimental herd was divided in five groups each composed of five randomly selected animals. Group 1 was challenged with T. congolense, Group 2 with T. vivax, Group 3 was inoculated with T. congolense followed by a cross-superchallenge with T. vivax, Group 4 was inoculated with T. vivax followed by T. congolense cross-superchallenge. Animals in Group 5 were used as controls. Both T. vivax and T. congolense cross-superchallenges were carried out on Day 14 subsequent to respective initial T. congolense and T. vivax inoculations. All challenges were performed by intradermal needle inoculation of stocks of trypanosome bloodstream forms. In challenged animals (Group 1 to 4), parasitaemia profiles and packed red cell volumes (PCV) were measured for four months. Weight changes were recorded monthly and daily weight gain (DWG) computed. All cattle challenged with T. congolense became parasitaemic. Conversely, one animal in Group 2 and two in Group 3 never displayed patent T. vivax parasitaemia. Both in single (Group 1), initial (Group 3) and cross-superchallenged (Group 4) cattle higher percentage of positive blood samples and higher parasitaemia level were obtained following T. congolense than T. vivax inocula (Group 2, 3 and 4) (P<0.04 or greater). Overall the pre-challenge period, PCV values and DWGs were nearly identical in the five groups. Conversely, over the post-challenge period, cattle singly, initially and cross-superinoculated with T. congolense (Group 1, 3 and 4) displayed lower PCV values and DWGs in comparison with both control animals (Group 5) and with singly T. vivax challenged cattle (Group 2) (P<0.05 or greater). No difference in mean PCV levels and DWGs was found between animals in Group 2 and cattle in Group 5. It was concluded that trypanotolerant N'Dama cattle suffered more from T. congolense and mixed T. congolensel T. vivax infections, while pure T. vivax infection did not produce appreciable negative effects on their health and productivity. Therefore, considering that tsetse and trypanosomosis control campaigns are costly and are justified only when derived economic benefits exceed those of control, and also that an ample mosaic of farming systems exists in West Africa, species-specific trypanosome prevalence and relative impact should be assessed in various cattle populations and breeds differing in trypanosome susceptibility before advising any intervention. Moreover, virulence and related effects of T. congolense and T. vivax endemic stocks on health and productivity in local cattle populations should also be estimated in order to counsel appropriate economic protection measures against trypanosmosis, i.e. vector control and/or strategic use of trypanocidal drugs.