EFFICACY OF MORANTEL SUSTAINED-RELEASE TRILAMINATE BOLUS AGAINST GASTROINTESTINAL NEMATODES IN GRAZING DAIRY CALVES IN KENYA

The efficacy of morantel sustained release trilaminate (MSRT) bolus ag ainst gastrointestinal nematodes was evaluated under field conditions over a 10-month period. Twenty weaner calves were randomly divided int o 2 groups of 10 calves each and grazed from March to December on adja cent, similarly contaminated paddocks. Group 1 calves (T-1) served as untreated controls while group 2 calves (T-2) were dosed at turnout wi th MSRT bolus designed to release morantel tartrate continuously for 9 0 days. The efficacy of MSRT was assessed by comparison of parasitolog ical data (faecal worm egg counts, herbage larval counts, worm counts from tracer calves and set-stocked trial calves, determination of haem atological parameters and pepsinogen levels), weight gains and clinica l status of the animals. Faecal egg counts fr om the treated group (T- 2) were reduced by 100% (P < 0.001) following treatment and remained s ignificantly (P < 0.05) lower than counts from T-1 calves up to trial termination. The use of MSRT bolus resulted in a reduction of 92% (P < 0.001) in the number of gastrointestinal nematodes in set-stocked cal ves at the end of the study and a 55 to 85.7% I reduction in herbage l arval infectivity as reflected in lowered parasite burdens in tracer c alves. At the trial termination, the control calves had gained on aver age (+/-s.d.) 59.4+/-4.8kg (200.0+/-7.4g day(-1)) and the treated ones on an average 128.6+/-10.5kg (530.0+/-13.1g day(-1)).