Changing the sex ratio at birth in lambs, calves and deer: Implications for productivity and genetic gain in breeding flocks and herds in New Zealand

W.H. McMillan

AgResearch, Ruakura Agriculture Centre, Private Bag 3123, Hamilton, New Zealand

Proceedings of the New Zealand Society of Animal Production. 1993, 53: 259-262

Survival rates to weaning in sheep, beef cattle and deer favour females by between 2 and 7 percentage units. Conversely, weaning weight favours males by 0.5 to 4.4 kg in sheep, 4 to 26 kg in beef calves and about 2-3 kg in red and fallow deer. Productivity at weaning time (ie weight of offspring per pregnant female) is increased by manipulating the sex ratio to all males, by only about 2% in each of the species. In self-replacing ewe and beef breeding systems, within-herd genetic gain is maximal over the range of 25 to 55% of males born and reduces dramatically beyond this range. Overall, there appears to be limited scope for reliably improving productivity to weaning and genetic gain in breeding flocks and herds by manipulating the sex ratio at birth. An analysis of the post weaning benefits is thus urgently required. Keywords: NZSAPAB; Sex ratio; sex effects; biological efficiency; sheep; beef cattle; deer.

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Last Updated 25-01-1997