Amongst individuals that produce multiple ovulations, and conceive, a variable proportion fail to deliver all potential offspring at term. This source of reproductive inefficiency has been termed partial failure of multiple ovulation (PFMO). In the case of twin ovulators, PFMO is manifest as single births. Most reports in the literature have attributed PFMO to uterine capacity or efficiency factors. An alternative model is proposed, in which it is assumed that a given reproductive outcome is determined by independent binomial effects of embryos and uterine/maternal factors. Using this model, it can be demonstrated that PFMO in twin ovulators can only occur because one of the two embryos is not competent to survive - that is, the uterine/maternal component plays no role in determining variation in PFMO. It follows that in pregnant farm animals with twin ovulations 100% twin births is possible, but is only constrained by low embryo quality. All published data examined to date in sheep cattle and goats are consistent with this alternative model.

WH, McMillan

Proceedings of the New Zealand Society of Animal Production, Volume 56, , 362-364, 1996
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