Variation in gestation length as breeding season advances in Bruna dels Pirineus beef cattle breed

The variation in gestation length according to the time lapse from the onse t of the breeding season until the day of mating was investigated in the Br una dels Pirineus beef cattle breed. A total of 359 gestations belonging to five breeding seasons were analysed. Average gestation length under natura l service was 288.6. Gestation length tended to increase significantly (p < 0.05) to about 1.5 days in cows that were mounted in the two last thirds o f the breeding season. The effects of domestication on birth synchrony are discussed.