Fertilization Failure and Embryonic Mortality in Parous and Nonparous Beef Cattle1

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Abstract
One hundred and two nonparous females, 18 to 24 mo old, and 55 parous or multiparous beef females, 3 to 12 yr old, were mated naturally (d 0) and slaughtered on d 2 to 5, 6 to 8 or 14 to 16 of gestation. Each reproductive tract was flushed with phosphate-buffered saline, and the flushings were searched for an oocyte or embryo. Parous females had a higher (P<.05) fertilization rate than nonparous females. In nonparous females, reproductive failure was attributed equally to fertilization failure and embryonic mortality, which had occurred or was occurring by d 8 of gestation. In parous females, reproductive failure was attributed entirely to embryonic death. About 67% of this embryonic mortality had occurred or was occurring by d 8 of gestation; the other 33% occurred between d 8 and 16 of gestation. These findings show that in both nonparous and parous beef females, a large portion of the reproductive failure occurs by d 8 of gestation and would not have any noticeable influence on length of the estrous cycle. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science.

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