Effect of selection for productive traits on internal parasite resistance in sheep

J.C. McEwan, P. Mason, R.L. Baker, J.N. Clarke, S.M. Hickey, K. Turner

AgResearch, Invermay Agricultural Centre, Mosgiel, New Zealand

Proceedings of the New Zealand Society of Animal Production. 1992, 52: 53-56

Host resistance to internal parasites, as measured by faecal egg count and dagginess was investigated in ram lambs born in the 1981-83 years (approximately generation 3) from the Woodlands selection lines. Lines were selected for either: number of lambs born, 100 day weight, hogget fleece weight and a production index in which all three traits are combined; a fifth line was a randomly selected control. Ram lambs were drenched with anthelmintic and then exposed to contaminated pasture for a period of 6-7 weeks and then faecal sampled. Total plasma protein, albumin and pepsinogen were measured.

The results demonstrated significant variation between selection lines in faecal egg count, dag score, liveweight gain, wool growth and blood plasma parameters. Between selection lines, faecal egg count was positively correlated with liveweight gain (0.95) and wool growth (0.41). Blood pepsinogen and total blood protein were both negatively associated with faecal egg count and liveweight gain (correlations of -0.51 to -0.90).

Using sire variation within selection line (progeny of 65 sires) produced heritability estimates of 0.13 ± 0.07 and 0.25 ± 0.09 for strongyle and Nematodirus faecal egg count respectively. Significant positive genetic correlations between strongyle faecal egg count and hogget fleece weight were observed.

Keywords: NZSAPAB; Sheep; genetic correlation; gastrointestinal parasites; selection; wool; liveweight.

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Last Updated 25-01-1997