Correlated responses in fleece weight to selection for divergence in
faecal nematode egg count in New Zealand Romneys and Perendales
C.A. Morris, S.A. Bisset, A. Vlasssoff, R.L. Baker, T.G. Watson,
D.M. Leathwick and M. Wheeler
AgResearch, Ruakura Agricultural Research Centre, Private Bag,
3123, Hamilton.
Proceedings of the New Zealand Society of Animal Production. 1997,
57: 26-28
Three selection experiments, two involving Romneys (at
Wallaceville and Ruakura) and the third involving Perendales (at
Ruakura), have resulted in breeding lines showing significant divergence
in faecal nematode egg count (FEC), under natural challenge. The High
and Low FEC lines in each experiment experienced 18, 8 and 11 years of
selective breeding respectively to 1996. The geometric means of FEC in
the three experiments were 7.3, 2.0 and 4.5 times greater in the High
than the Low lines, equivalent to divergences of 2.12, 0.80 and 1.27
phenotypic standard deviations. In the present analysis, the High and
Low lines were compared for greasy fleece weights using both yearlings
(YFW) and mixed-age ewes (EFW). Relative to the Low lines, the
corresponding High lines had greater YFWs by 14.6±3.0, 7.9±2.4
and 5.3±3.1% respectively (mean of three, 9.1±1.6%), and they
had greater EFWs by 14.9±1.7, -3.2±3.8 and 8.0±2.7% (mean
of three, 10.9±1.3%). The conclusion is that single-trait selection
for reduced FEC in Romneys and Perendales is associated with reduced
greasy fleece weight, when they and less resistant animals graze
together.
Keywords: NZSAPAB;
sheep; nematode parasites; selection; faecal egg count; fleece weight.
Last Updated 12-09-1998
