Data from mature ewes repeatedly re-immunised against androstenedione or oestrone in 3 trials at the Ruakura (Coopworths), Wairakei (Perendales) and Whatawhata (Romneys, Coo9pworths and Perendales) Animal Research Stations, were analysed to estimate the repeatability of ovulation rate and number of lambs born per ewe. Immunisation responses were within the range of those reported previously (Smith, 1985). Between-year repeatability estimates were on average similar for immunised and non-immunised ewes. The unweighted average of the estimate was 0.29 for ovulation rate and 0.009 for number of lambs born, consistent with published values. The results suggest that the joint contribution of genetic and permanent environmental sources of variation to phenotypic differences between animals is similar under both physiological states. The high repeatability of ovulation rate in comparison with number of lambs born supports other published indications of its possible value for improvement of reproductive rate through selection.

G, Ahlborn-Breier, and BW Wickham

Proceedings of the New Zealand Society of Animal Production, Volume 46, , 83-86, 1986
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