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Estrus after Conception in a Herd of Holstein-Friesian Cattle¹

Department of Dairy Science, State College of Washington, Pullman

ABSTRACT

Estrus after conception was observed during 5.6% of 6,751 reproductive periods which terminated in nonabortive calvings. Cows in their second and third reproductive periods averaged 7.5%, as compared with little more than 4%, for animals in their first or more than seventh (P < 0.05). Of 1,905 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 estrous cycles after conception was 43 ± 1.9 days. The modal length of 21 days was observed in 5.6% of the 534 cycles observed. Fifty-five per cent showed estrus within 35 days after conception. Reproductive performance of cows during periods of postconception 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 postconception estrus. The expected rate was 42% if the two phenomena were unrelated. Postconception 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%. Postconception estrus occurred most frequently in November, December, January, and June, and least frequently in March, July, August, and October. The monthly differences were not significant.

¹ Scientific Paper No. 1619, Washington Agricultural Experiment Stations, Pullman. Project W-2 (888). This research was financed in part under Regional Research, Research and Marketing Act, Section 9b3, Public Law 733.

² Present address, Quaker Oats Co., Merchandise Mart, Chicago, Illinois.