| Abstract: | The efficacy of the morantel sustained release bolus in controlling gastrointestinal and lungworm parasites when used in first-season grazing animals which followed older animals onto spring pasture (deprime system) was assessed in three trials conducted in Normandy, France. In each trial first-season grazing calves were equally allocated onto two separate but equivalent paddocks where they remained throughout the grazing season. A morantel sustained release bolus was administered to one group of animals at turnout, the other group remained as controls. The effect of the treatment on contamination of pasture (herbage larval counts and tracer worm counts), on faecal worm egg and lungworm larval counts, and on weight gain performance of the principal animals was assessed. In all three trials, worm egg output in the bolus-treated animals was substantially lower throughout the season compared with the control animals. Worm burdens of tracer calves grazing pastures of the treated cattle were also reduced compared with tracer calves grazing control pastures. Clinical parasitic gastroenteritis occurred in the control animals but not in the bolus-treated animals in one trial. Overall the bolus-treated animals outperformed the controls by a mean weight gain advantage of 10.5 kg (P less than 0.01). |
