A morantel sustained-release bolus for the control of gastro-intestinal nematodes in grazing calves

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Abstract
Prophylactic (summer) and/or therapeutic (autumn) administrations of an intra-ruminal sustained-release bolus (MSRB) containing morantel tartrate were compared for the control of gastro-intestinal nematodes in grazing dairy calves over an 8-month period (December to August). The MSRB was designed to release morantel tartrate at 150 mg/day for 90 days. Treated and untreated groups of calves grazed separate replicated pastures. Both groups of calves receiving the MSRB at the beginning of summer showed a significant mean liveweight advantage (17.7 kg and 20.7 kg for the summer and summer/autumn treated groups, respectively) at the end of the trial period, when compared with untreated calves. The liveweight advantage of calves receiving the MSRB in autumn only (6.5 kg) was not significantly different from that of the controls. Both the summer and autumn administrations of the MSRB prevented the accumulation of Pre-Type II burdens of Ostertagia spp. Retention rates of the MSRB were high and chemical analysis of faecal samples indicated a fairly constant release of the anthelmintic over the predicted 90-day period. The results indicate that the MSRB is potentially useful for the control of gastro-intestinal nematodes, and particularly for the production of ’safe’ pasture. The MSRB could provide an effective alternative to integrated control based primarily on grazing management.

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