A study on the use of berenil and samorin for the treatment and control of bovine trypanosomiasis in a medium challenge area

Abstract

In November 1978 a study was initiated to evaluate two trypanocidal drugs, the prophylactic Samorin and the curative Berenil as to their efficacy for supporting long-term maintanance of Boran cattle in a 'low' to 'medium' trypanosome challenge area of Kenya. Seven groups of 281 Boran cattle were maintained in a tsetse-infested area with periodic trypanocidal drug treatment for 24 months. The animals of two groups were treated individually with Berenil at 3.5 mg/kg body weight when clinically affected by trypanosomiasis and/or when the PCV fell below 20. The animals of one group were all treated with Berenil at 3.5 mg/kg body weight every 2 weeks. Three groups of animals were treated with Samorin at 3-dosage levels of 0.25 mg/kg; 0.5 mg/kg and l.O mg/kg. In these Samorin groups, the different age groups, calves, heifers and cows within each of the 3 dosage groups were handled separately.The need for treatment with Samorin for any age group within each dosage group followed a positive microscopic diagnosis of trypanosomiasis in an individual animal. One group of animals remained untreated throughout the study period and served to monitor trypanosome pathogenicity. The effects of the various drug regimes used were studied, the growth rates of the various groups compared and the economic losses due to trypanosomiasis determined. The trypanosome challenge in the study area was variable out was generally graded as 'low' throughout the experimental period. The prevalence of both trypanosoma.congolense and T. vivax were high during the initial infections but T. congolense became the dorminant species diagnosed in subsequent infections. The tsetsefly infection rate was 1.5% with Glossina pallidipes being the most important fly. Cattle treated as groups vvith Samorin qrew better than animals treated individually with Berenil. There was no evidence of either age resistance or drug resistance to the disease. Mortality due to trypanosomiasis in the untreated animals was estimated at 34% per annum. The highest percentage of calf mortality was recorded in the untreated control group while the highest number of live calves born per cow per annum orginated from cows treated with Samorin at 0.5 and 1.0 mg/kg body weight. An economic study indicated that without protection against trypanosomiasis the financial loss due to death and reduced weight gain was considerable.