Trypanosomiasis: A study on the development and control in three breeds of Goats

Abstract

Trypanosomiasis is an important disease of tropical Africa which greatly limits livestock production. This disease has had extensive study in large ruminants while relatively little has been carried out in small ruminants. This study was carried out using three breeds of goats, namely, Toggenburg X East African, Galla X East African and the East African goats* Three aspects were considered; effect of chemotherapy on production parameters, comparative trypanotolerance among the East African goats and the relationship between tsetse fly numbers, rainfall, relative humidity and infection rates. Each breed of goat was divided into an experimental and a control group. The experimental groups got a monthly infection of isometamedium chloride (Samorin^ "^) at the dose rate of 0.5 mg/kg body weight. The drug was administered intramuscularly at the side of the neck. The production parameters considered in this study were packed cell volume and body weight. The packed cell volume was measured every two weeks while the body weight was taken once every month. The haematocrit centrifuge technique was used for trypanosome detection and the morphological identification done after staining with Giemsa diluted 1:10 in neutral distilled water. Among the control groups the body weights, the changes in packed cell volume, infection rates and mortality rates were compared. Rainfall and relative humidity were measured on a daily basis while tsetse flies were caught by putting out Challier traps for four consecutive days every month. The flies were identified into species and sex and the number caught per trap per 24 hours worked out for every month. Where a breed of goat was involved in mating, the fertility rate3 among an experimental or a control group was evaluated with regard to the proportion of animals kidding, the proportion of animals twinning and the mean birth weight of the kids. The results indicate that, the groups of animals receiving samorin had higher mean packed cell volume values and higher weight gains than the controls that were not receiving any samorin* The results on fertility show that the animals in the treatment groups had higher proportions of animals kidding and twinning. The East African goats showed a higher degree of trypanotolerance than the other two breeds as manifested by the packed cell volume values and the mortality rates due to trypanosomiasis. The Galla X East African goats had an intermediate degree of trypanotolerance between the East African and the Toggenburg X East African goats. The Toggenburg X East African goats showed an increase in infection rates following an increase in tsetse fly numbers. The East African goats also showed a similar increase but of a much lower magnitude. The Galla X East African goats showed changes in infection rates which were not concomitant with changes in tsetse fly numbers. The cost of controlling trypanosomiasis using aamorin on a monthly basis at the dose rate of 0.5 mg/kg body weight per tropical livestock unit was worked out. Gome of the economic losses resulting from trypanosomiasis were also worked out. It was -ound that the cost/benefit ratio was highest among the Toggenburg X East African goats followed by the Galla X East African goats. It was lowest among the East African goats which manifested the highest degree of trypanotolerance.