A note on detection of oestrus in cattle bred by artificial insemination, and the measurement of embryonic mortality

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Abstract
SUMMARY: Insemination and calving dates were obtained for 2618 British Friesian cows served twice by artificial insemination, the first time unsuccessfully, the second time successfully. The intervals between the two inseminations formed a multi-modal set of normal distributions with peaks at 21-day cycles. The standard deviation of the Kth distribution was 3·0y/K days, with about 58·5% of eligible animals submitted at each cycle. Nearly 84% of all intervals conformed to the normal distributions, suggesting that embryonic mortality occurred in about 16% of cases following the first oestrus after insemination.