Further studies on the anthelmintic effect of a sustained release pre-grazing treatment with morantel in grazing cattle in Sweden.

The efficacy of a morantel sustained release bolus (MSRB) to control gastrointestinal parasitism in first season grazing cattle was assessed under field conditions in Sweden. The MSRB was administered orally to calves immediately prior to turnout onto spring pastures in May, 1979, or in mid-season (July). The level of pasture contamination with infective larvae was reduced by 99 per cent in September by treatment at turnout. The corresponding figure was 89 per cent when the MSRB was administered in July. There was a 95 per cent reduction in worm burdens acquired over the entire grazing season in cattle treated in the early season and a 44 per cent reduction in worm burdens of cattle treated in the mid-season. During the 132 days grazing period a 19.1 kg (p less than 0.01) mean weight gain advantage was achieved by the early season treated animals, while a 10.0 kg mean weight gain advantage was achieved by the mid-season treatment. The weight gain advantage at the end of the grazing season in the early treated cattle increased continually during the winter with a resultant mean difference of 44.4 kg (p less than 0.01) by April 1980. Over the same period the mean weight gain advantage of the mid-season treated animals gradually fell to a final of 5.5 kg.