Estrus after Conception in a Herd of Holstein-Friesian Cattle

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Abstract
Estrus after conception was observed during 5.6% of 6751 reproductive periods which terminated in nonabortive calvings. Cows in their 2d and 3d reproductive periods averaged 7.5%, as compared with little more than 4% for animals in their 1st or more than 7th (P <0.05). Of 1905 cows calving one or more times 18.3% showed estrus after conception at some period of their reproductive life. Estrus occurred after conception more than one time in 18% of the reproductive periods showing estrus after conception. Average length of estrus cycles after conception was 43 [plus or minus] 1.9 days. The modal length of 21 days was observed in 5.6% of the 534 cycles observed. Fifty-five percent showed estrus within 35 days after conception. Reproductive performance of cows during periods of post conception estrus was comparable to herd average with respect to services per conception, calving interval, abortion, and retained placentae. Twinning was 1.2% higher than herd average. Percentage male calves (56.8%) was significantly higher than the average for the herd. Cystic tendency was observed at some time during the reproductive life of 70.5% of the cows observed having post conception estrus. The expected rate was 42% if the 2 phenomena were unrelated. Post conception estrus followed observance of cystic tendency in the same reproductive period 31.4% of the time as compared with an expected rate of 17.6%. Post conception estrus occurred most frequently in November, December, January, and June, and least frequently in March, July, August, and October. Monthly differences were not significant.

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