Causes of Fertilization Failure in Repeat Breeding Cattle

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Abstract
One hundred and four ova were recovered from 150 cows (69.3%), and 58 of them were fertilized (55.8% of the ova). The fertilization rate was significantly lower (48.5%) for cows bred during the 1st 8 hr. of heat than for those bred 16 hr. later (68.6%). Breeding twice during the heat period (during the 1st 8 hr. and again 16 hr. later) did not improve the fertilization rate (66.7%). Abnormalities causing fertilization failure were as follows: ovulation failure, 8.7% of the cows bred; oviduct obstructions, 6.7%; abnormal ova, 3.3%; ovarian adhesions, 2.0%; and endometritis, 3.3%. Ova could not be found in 17.3% of the cows, even though no abnormalities were apparent to account for their absence. In 24.7% of the cows, there was no apparent explanation for fertilization failure. The presence or absence of bacteria in the cervix and uterus had no effect on fertilization rate. When uteri sections were studied histologically fertilization rates were somewhat lower for cows having cystic uterine glands, thin mucosae, or endometritis. However, arterial elastosis and mucosal edema did not affect fertilization rates.