Observations on a herd of beef cattle maintained in a tsetse area. II. Assessment of the development of immunity in association with trypanocidal drug treatment.

Three groups of Boran cattle were maintained under different trypanocidal drug regimes for 29 months in an area of "medium" tsetse challenge. The development of immunity to trypanosmiasis in the cattle was assessed on the basis of changes in trypanocidal drug requirement, development of parasitaemia, ability to maintain normal blood values, growth and response to challenge after the withdrawal of the drugs. Observations were also made on serum antibody content by immunofluorescence and on serum immunoglobulin levels. Cattle treated with Berenil on the development of clinical disease developed a partial immunity to trypanosomiasis after two years. Cattle treated as a group with Berenil on the development of patent parasitaemia in any one animal of the group did not develop immunity. Cattle treated as a group with Samorin using the same criterion for treatment developed a degree of immunity to the disease. It was concluded that group treatment with Samorin was the most suitable of the three regimes examined for the maintenance of beef cattle is a tsetse infested area.