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Breeding for worm resistance- whole farm benefits

Johan Greeff, L.J.E. Karlsson


\"Resistance of sheep worms against the available anthelmintic drenches is increasing. Breeding sheep for resistance against gastrointestinal parasites is the only long-term solution. Research has shown that breeding for worm resistance is a highly feasible option and that genetic gains of more than 2% per year can be achieved without loss of production. Replicated field trials in which resistant animals were managed separately from unselected control sheep showed that there was a 10-fold difference in worm egg counts between resistant and control ewes. Resistant ewes were 18% heavier than the controls at the time of peak worm-challenge in a Mediterranean environment. At weaning, there was a five-fold difference in worm egg counts between resistant and control lambs, which resulted in an improvement of weaning weight of up to 22%. It is therefore better to include selection for worm resistance in breeding programs than to omit it for fear of diminishing future genetic gains in other traits.


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