Progress on genetic studies of resilience to nematode parasites in
sheep
C.A. Morris and S.A. Bisset
AgResearch, Ruakura Agricultural Research Centre, Private Bag 3123,
Hamilton, New Zealand.
Proceedings of the New Zealand Society of Animal Production, 1996,
56: 91-93
Recent studies on 3- to 7-month-old lambs have shown that there is
genetic variation in the ability to withstand the effects of roundworm
challenge and thus maintain acceptable performance (high growth, low
dags) when left undrenched for extended periods. This trait is generally
referred to as resilience. The heritability of resilience has proved to be low
(three yearsí data, with 213 sire groups and two separate approaches to
measuring resilience gave estimates of 0.10±0.03 and 0.14±0.03).
Nevertheless progeny testing should successfully identify genetically
resilient rams for use. Resistance to nematode infection, measured in terms
of faecal egg count (FEC), is also known to be inherited in sheep, and
studies of selection for low FEC have successfully improved resistance.
However, resilience and resistance appear to be genetically independent. A
selection experiment for high vs low resilience was initiated in 1994, and the
first yearís results are reported here. Four progeny-tested rams with high
resilience (RL+) and four with low resilience (RL-) were inter se mated to
outlier RL+ and RL- ewes. Progeny were grazed together on infective
pasture, with minimal drench treatment. Relative to RL- progeny (n=74),
RL+ progeny (n=84) had 2.0 kg greater weaning-to-autumn gains (+17%,
P<0.001), 2.2 kg greater live weights in April (+7%, P<0.01), and a
significant advantage in yearling weight (P<0.05). However, there was no
significant difference in dag score, or in January or March FEC. There was a
0.24 kg increase in yearling fleece weight (+10%, P<0.01). The results show
that selection for resilience is possible and that, provided care is taken to
avoid sires with high FEC, improved resilience in lambs should lead to
lower drenching requirements without jeopardising production.
Keywords: NZSAPAB;
nematodes; faecal egg count; resistance; resilience; genetics; sheep.
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Last Updated 18-03-1997
