Genetics of resilience to nematode parasites in young Romney sheep)—use of weight gain under challenge to assess individual anthelmintic treatment requirements

摘要

Abstract The performance of 2997 male Romney lambs, sired by 102 rams and born in spring 1992 on four farms in southern North Island, was measured under a selective anthelmintic treatment regime to obtain genetic information on the resilience of grazing lambs to nematode challenge. The basis on which selective treatment decisions were made was modified from that of an earlier study (which used farmer assessment of body condition and dag score) in an endeavour to make the procedure more objective. On the first two drenching occasions after weaning, only those lambs whose liveweight gain was below an acceptable threshold, defined using data from flock mates, received anthelmintic treatment (selective drenching). A resilience score for each animal was derived from drench requirement data either as age at first drench (normalised to include animals never drenched) (NAD), or as a binary code denoting whether or not the animal had been drenched by the end of the selective drenching regime (BY2). Productivity, b...