A review of the influence of liveweight and flushing on fertility made in the context of efficient sheep production

F.R.M. Cockrem

Ruakura Animal Research Station, Hamilton

Proceedings of the New Zealand Society of Animal Production. 1979, 39: 23-42

The assumption that the increases in efficiency of feed conversion normally associated with increases in fertility will accrue when the increase in fertility is achieved via increased liveweight is questioned. The biological components of fertility are reviewed as the possible limiting stages in lamb production. These are the oocyte populations and their development, ovulation rate, embryonic loss, lamb mortality and lamb growth. The interdependence of these stages is emphasized and the possible genetic relationships are illustrated from the results of published mouse selection experiments.

The current evidence on relationships between fertility and ovulation rates and liveweight is summarized. Possible developmental origins of relationships between size and ovulation rate are listed.

The remainder of the review is concerned with the dynamic effects of liveweight and summarizes the evidence on how body reserves and their hormonal control might be related to ovulation rate and the annual cycle of lamb production. The final section suggests some experimental approaches which could be used to follow up some of the ideas reviewed.

Keywords: NZSAPAB;

Last Updated 12-09-1998