Resistance and the 'self-cure' phenomenon were examined in Coopworth lambs and Saanen kids when they were between 6 and 8 months old. The animals had been reared on pasture from birth until February 1987 at which time they were treated with anthelmintic and withheld from pasture for two weeks. They were given Trichostrongylus colubriformis (500 infective (L3) larvae kg-1) weeks after the initial dose. Faecal egg counts estimated at weekly intervals were significantly higher in kids than in lambs throughout the experiment. Furthermore, a strong acquired resistance was effected in the lambs subsequent to and as a result of the second dosing. The kids failed to show a similar response. Worm counts estimated at necropsy confirmed that spontaneous rejection, against Trichostrongylus and Ostertagia had been produced only in the lambs. These results how clearly that there are some significant differences between grazing lambs and kids in their ability to acquire and sustain a resistance to nematode parasites.

F, Colomer-Rocher, and AH Kirton

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 147-152, 1989
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