Effect of the morantel sustained-release bolus, used during one grazing season, on the sensitivity of Ostertagia and Cooperia to morantel tartrate in calves
Newby, T.J.; Yazwinski, T.A.; Presson, B.L.; Holtzen, H.M.; Bischoff, M.J.; Featherstone, H.E.
American Journal of Veterinary Research 46(2): 424-425
1985
ISSN/ISBN: 0002-9645 PMID: 3994107 Document Number: 243962
Infective 3rd-stage larvae of Ostertagia and Cooperia, obtained from the faeces of nonmedicated and morantel sustained-release bolus (MSRB)-treated calves, were orally administered to two groups (six per group) of parasite-free calves. After a 42-day maturation period, a therapeutic dose of morantel tartrate was given to half the calves in each group. PM nematode counts seven days after treatment showed morantel to be equally effective against the nonmedicated-derived and MSRB-derived nematode populations. The sensitivity of Ostertagia spp. and Cooperia spp. to morantel tartrate, therefore, was not diminished after use of the MSRB for a single grazing season.