The effect of the morantel sustained release bolus in young cattle under Norwegian conditions
Tharaldsen, J.; Helle, O.
Nordisk Veterinaermedicin 34(12): 464-470
1982
ISSN/ISBN: 0029-1579 PMID: 7162961 Document Number: 194739
Autumn-born bull calves were treated with a morantel sustained release bolus (MSRB) at the beginning of the grazing period. Comparisons were made between egg counts, pasture larval counts and live weight gains of these and of a group of untreated controls. The pastures used for the treated calves and for a control group had high numbers of overwintered nematode larvae in the spring. The treatment with the MSRB prevented the establishment of larvae taken up with the grass, as shown by low numbers of nematode eggs in the feces, good clinical condition and uniform weight gain. The treatment further prevented the development of a new generation of larvae in the pasture, which occurred on the area of the control calves from about Aug. 1 due to eggs produced by these animals. The untreated calves showed high fecal egg counts 6 wk after turnout and severe clinical symptoms, including deaths. Their weight gain for the whole grazing period was 44.2 kg below that of the treated animals (P < 0.001), and to this must be added the losses due to 2 deaths. The greatest group difference in weight gain occurred during the first 2 mo. on pasture, which shows that the main damaging effect was caused by the overwintered larvae. The principle of the sustained release bolus seems to be well suited under Norwegian conditions, where substantial numbers of larvae may survive the winter in the pasture, and where a fairly short grazing season will truncate the period in autumn when the bolus is no more active.