Genetic studies of resilience of Romney sheep to nematode
challenge in New Zealand
C.A. MORRIS, S.A. BISSET, A. VLASSOFF, A.D. MACKAY, K.
BETTERIDGE, M.J. ALDERTON, C.J. WEST AND B.P. DEVANTIER
AgResearch, Ruakura Agricultural Research Centre, PB 3123,
Hamilton, New Zealand
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Proceedings of the New Zealand Society of Animal Production 2001.
61: 92-95
"Resilience" in sheep can be defined as the ability to withstand
nematode challenge, and to maintain acceptable health and productivity,
with minimal reliance on anthelmintic treatment. One heritable component
trait is Total Drench Requirement (TDR), which is measured in lambs
managed on a regime of "drench-on-demand" (where Trichostrongylus and
Ostertagia are the predominant nematode genera in New Zealand sheep). A
breeding experiment was established in 1994, selecting for increased
resilience in Romney lambs. Currently, breeding ewes in the experiment
are subdivided between Ballantrae, where four genetically equivalent
sub-groups graze separate farmlets year-round, under Non-Chemical versus
Conventional management (AgResearch’s Low-Chemical Farming Systems
Programme), and Wallaceville, where an Elite Resilient line was
re-established in 1999 alongside the Control Faecal Egg Count (FEC)
line. Selection responses up to 1999/00 in the Elite Resilient-line
lambs (relative to the Control line) included a 27% greater post-weaning
weight gain (GAIN: Dec. to Apr.), a 0.48 unit reduction in dags, and a
45% reduction in TDR (Dec. to Apr.). A favourable genetic correlation
(-0.54) was recorded between TDR and GAIN in lambs, whilst that between
TDR and log FEC was -0.17 (not significant). Mean autumn weights in
lambs at Ballantrae were 5.8 kg (18%) lower in the Non-Chemical than
Conventional treatment groups (P<0.01). Through intense genetic
selection, 51% of Elite-line ram lambs are now resilient enough for
low-chemical or organic production systems.
Keywords: NZSAPAB;
Last Updated 7/08/01
