Trials with the morantel sustained release bolus in young cattle on nematode contaminated pasture, with treated and control animals grazed together.

The effect of the morantel sustained release bolus was studied in a group of first-season grazing calves kept together with an untreated control group. The groups were kept together to eliminate the uncontrollable influence of uneven nutritional conditions on weight gain when groups are kept on separate pastures. The calves were given one bolus just before turnout and a second three months later. In the treated calves, the number of nematode eggs in the faeces was kept on a low level during most of the grazing season, except for a slight rise in the egg counts after two months of pasture, before the second bolus was given. At the end of the 5 months' grazing period the live weight gain of the treated calves was 29.1 kg greater than that of the control calves (p less than 0.01), and the treated animals were in a far better condition than the untreated. The experiment showed that the MSRB prevented a significant weight loss due to gastrointestinal nematodes.