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A Study of the Gestation Period of Holstein-Friesian Cows¹

Division of Dairy Husbandry, Agricultural Experiment Station, State College of Washington, Pullman, Washington

ABSTRACT

1. The average number of days of 2,824 gestation periods studied that terminated with single births was 279.9 ± 0.063. Twins were born in 86 cases following gestation periods averaging 275.5 days.
   
2. The length of gestation periods varied from 262 to 296 days. Almost 75 per cent of all calves were dropped from the 275th to the 285th days inclusive. Only 1.7 per cent were carried for periods shorter than 270 days and 2.7 per cent were carried for 290 days or longer.
   
3. Male calves were carried an average of one day longer than female calves.
   
4. An increase in the length of gestation periods of approximately one and one-half days was observed as the age of the dams increased from two to six years. After the age of six years was reached there seemed to be a tendency for the gestation periods to become slightly shorter.
   
5. The gestation periods of calves sired by some bulls were definitely higher or lower than the average, indicating by their uniform divergence from the mean the possibility of paternal influence.
   
6. The least variation in length of gestation observed for 29 cows that had each produced six or more calves was six days. The greatest variation was 20 days. The length of gestation periods of some cows were quite uniform, while others varied widely.
   
7. Eleven exceptionally high producing cows were carried in dam an average of 278 days, or about one and one-half days less than the average for all females. The periods varied from 262 to 289 days.
   
8. In comparing the gestation periods of the above cows with the gestation periods of the calves they produced, it was found that four of the eleven eases showed a decided tendency for the calves of a cow to have gestation periods similar in length to her own.
   

¹ Published as scientific Paper No. 191, College of Agriculture and Experiment Station, State College of Washington.