CONTROL OF GASTROINTESTINAL PARASITISM IN CALVES WITH ALBENDAZOLE DELIVERED VIA AN INTRARUMINAL CONTROLLED-RELEASE DEVICE

The efficacy of albendazole in an intraruminal controlled-release devi ce against gastrointestinal nematodes in calves was evaluated under fi eld conditions, Calf productivity was monitored during the first and s econd grazing seasons. Two groups of parasite-naive Holstein Friesian heifer calves were grazed from May to October on adjacent, similarly c ontaminated paddocks. One group was given a Captec bolus at turnout, t he other group was left untreated, Pasture larval counts peaked on the paddock grazed by the untreated calves at 23000 1 kg(-1) dry matter i n October. This precipitated clinical parasitic gastro-enteritis in th e untreated calves with a mean peak faecal egg count of 335 epg, high blood pepsinogen and gastrin concentrations and a mean worm. burden of 79 614 at 100 days post-tumour. Pasture larval counts on the paddock grazed by the treated calves remained less than 3000 1 kg(-1) DM and t he mean faecal egg count was zero until mid-August, peaking at 146 egg s per gram of faeces (epg) in October. The treated calves had body liv eweight advantage of 19 kg at the end of September, During the second grazing season the first season untreated calves were refractory to in fection. The first season treated calves showed signs of parasitic gas tro-enteritis, although not to the extent exhibited by a group of firs t season parasite-naive tracer calves which were grazed on the same pa ddock.