Reproductive Behavior of Females in a Subtropical Environment. I. Puberty and Ovulation Frequency in Brahman and Brahman X British Heifers

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Abstract
The ovaries of 252 Brahman heifers and 60 Brahman crossbred heifers at three ranches in North Central and South Florida were palpated at monthly intervals for different periods of time. The heifers came from well-managed herds with better than average nutritional levels. Puberty was determined by occurrence of the first corpus luteum. The average age of puberty for 83 Brahman heifers with complete data was 19.4 mo., with a range of 14 to 24 mo. Incomplete data from additional 41 heifers suggested that puberty occurred in some Brahman females as late as 26 mo. of age and earlier than 14 mo. The average age of puberty in 17 Brahman-Shorthorn heifers was 17 mo. with a range of 15 to 20 mo. In 5 crossbred heifers with incomplete data, puberty occurred earlier than 7 to 13 mo. of age. There was no significant difference in age at puberty due to season of birth or ranch location. There was a correlation between 205-day weaning weight and age of puberty of −.46 (P<.01) and −.41 (P<.05) for the Brahman and crossbreds, respectively. Brahman heifers exhibited a definite seasonal variation in sexual activity as measured by frequency of corpora lutea, and by size and tonus of the uterus. Sexual activity increased during the spring and was highest in the summer. After a low incidence of corpora lutea during the winter, it increased again during the second spring, especially following exposure to bulls. Seasonal fluctuation in frequency of corpora lutea did not occur in Brahman-British heifers. The crossbreds had a higher frequency of ovulation than Brahman females throughout the year. It is suggested that temperature, nutrition or the presence of bulls influences the levels and balance of the endocrine system, resulting in seasonal variation in sexual activity in Brahman heifers. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science

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