A simple epidemiological method for animal trypanosomiasis to provide relevant data for effective financial decision-making.

The epidemiology of bovine trypanosomiasis on Galana Ranch, Kenya was studied for one year (July 1980--June 1981), using measurements from an experimental population of 3 types of Boran cattle. The results were applied to the estimated ranch population at risk, and an attempt was made to measure the potential economic loss due to trypanosomiasis. The potential losses in beef production due to trypanosomiasis in the ranch population at risk at Galana were estimated at around K.Shs. 8900/km2, when the stocking rate was 14.2 Tropical Livestock Units per km2. The estimated potential loss in the total population at risk was approximately K.Shs. 5 million (around US$ 700,000 at 1981 values). These losses can be minimised by good management techniques based on accurate epidemiological information. Results indicated that Orma-type Boran steers are more resistant to trypanosomiasis than Galana-type Boran steers. Although both types showed similar mortality rates, untreated Orma animals which survived showed a similar growth performance to animals maintained under 3-month Samorin prophylaxis. Untreated Galana Borans lost 14% of their body weight when compared with animals maintained under 3-month Samorin. Also, 30% of the untreated Orma Borans never showed trypanosomes in their blood over the study period, while all corresponding Galana Borans showed parasites; this resulted in a lower measured attack rate in Orma cattle. In 1982, a combination of treating only those animals under trypanosome attack, relating the timing of chemotherapy to measured increased trypanosome attack, and the increased utilisation of the trypano-tolerant Orma Borans resulted in an annual saving of around US$ 110,000 in control costs and an increased land usage of approximately 5%.