Romney sheep selected for resistance to nematode infection, resilience to nematode challenge, or an index combining these traits, were evaluated alongside an unselected control line. Data from lambs born between 2000 and 2006 were analysed. Lambs grazed together, within sexes, while exposed to natural parasite challenge of predominantly Trichostrongylus sp. and Teladorsagia sp. Relative to the Control, the Resilient line was heavier at weaning (+7.6%) and in autumn (+14.5%), had 5.6% higher yearling greasy fleece weight (YGFW), and less dags (lower score) at 5 months of age by 0.72 standard deviations (SD) (all P <0.01). As expected, the two lines had similar post-weaning faecal worm egg count (FEC1). Compared with the Control, the Resistant line was lighter at weaning (-8.6%) and in autumn (-8.0%), had 14.9% lower YGFW and a higher dag score by 0.22 SD, whilst FEC1 averaged 16% of the Control value (all P <0.001). Performance of the Index line in growth and YGFW was 3.5 to 6.8% above that expected in a Resistant x Resilient cross. Conversely, FEC1 in the Index line was at least 31% higher than expected for a cross. We conclude that combining genes for resilience and low FEC by index selection is feasible.

M, Wheeler, CA Morris, and SA Bisset

Proceedings of the New Zealand Society of Animal Production, Volume 68, Brisbane, Australia, 138-141, 2008
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