In order to develop an experimental resource to understand the biology of superior recipients, each of 155 contemporary yearling heifers received 2 in vitro-produced embryos on 6 occasions during a 30-month period. The number of foetuses present were determined at Day 60 of pregnancy, and pregnancies terminated. Heifers were ranked for their aggregate pregnancy performance, and the highest and lowest 25 were retained. Mean pregnancy rates of all recipients ranged from 0.20 - 0.67 depending on transfer occasion. The mean ± s.e. pregnancy rate of the High and Low groups were 0.77 ± 0.07 vs. 0.11 ± 0.06 respectively (P<0.001). No significant differences were observed between the two groups in oestrous cycle progesterone profiles or follicular dynamics. We conclude that repeated twin embryo transfer can be used to identify recipients of high and low potential fertility, and that uterine, rather than simple ovarian parameters, may be better correlates with high pregnancy rate.

WH, McMillan, MJ Donnison, and SF Cox

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 248-251, 1998
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