Pregnancy rate to term after embryo transfer (ET) in cattle ranges from 30-50%. A model is proposed which partitions embryo survival into independent and binomial embryo and maternal components. Parameters for these two components can be used to calculate expected pregnancy rates. In 35 out of 36 sets of data in which pregnancy data were recorded following contemporary single and twin ET, or single and twin ovulation, expected pregnancy rate was either within 5 percentage units or one standard deviation of observed pregnancy rate. Pregnancy rate changes in single ET recipients or single ovulating females are equally sensitive to changes in the embryo and maternal components. In contrast, pregnancy rate changes in twin ET recipients or twin ovulating females are more sensitive to changes in the maternal component. In conclusion, these data suggest that the model adequately describes embryo survival and pregnancy rates. Accordingly, research to improve the maternal component seems warranted in order to improve reproductive success.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 218-221, 1997
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