The sexes of calves born in 1996 (n = 319,539) and 1997 (n = 408,381) to artificial insemination in selected herds were analysed to study the effects of region, dam breed, dam age, semen type, semen breed, semen age, and sires on the sex ratio of calves. There was a significant (P < 0.001) effect of semen type on sex ratio; frozen semen resulted in 1.66% and 1.24% more male calves than fresh semen, respectively, in the 1996 and 1997 seasons. There was also significant (P < 0.01) variation among sires in sex ratio, but the heritability estimate for sex ratio was low (h2 = 0.02). No other effects were significant. Industry-wide use of fresh semen will result in more heifer calves from which future replacements can be selected.
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 301-302, 2000
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