Pituitary and Hypothalamic Endocrine Changes Associated with Reproductive Development of Holstein Bulls

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Abstract
Sixty-five Holstein bulls were killed in groups of five at monthly intervals from birth to 12 mo. of age. Increases in bodyweight and anterior pituitary weight were linear during this period, except for a significant reduction in weight of anterior pituitary at 7 mo. Whereas the concentration of pituitary LH was greatest at 1 mo.(4.88 meg. NIH-LH-B3 equivalent per mg.), gland content was greatest at 6 mo. of age (2.83 mg. NIH-LH-B3 equivalent per anterior pituitary). But, the age-limits of puberty could not be precisely defined by any dramatic changes in pituitary LH. Estimated total plasma LH did not change significantly from birth to 2 mo., increased to 4 mo. and increased again between 6 and 10 mo. of age. Although luteinizing hormone-releasing factor (LRF) could not be detected in hypothalami from bulls less than S mo. of age, the increase in plasma LH between 6 and 10 mo. was associated with a marked simultaneous increase in levels of hypothalamic LRF. Concentration of pituitary FSH was greatest at 2 mo. (0.24 meg. NIH-FSH-S3 equivalent per mg.), but pituitary content was greatest at 5 and 6 mo. and both declined after 6 mo. of age. The data on pituitary FSH, hypothalamic LRF and plasma LH suggest that puberty in Holstein bulls commences at 2 mo. and is qualitatively completed by 10 mo. of age. Greatest changes occur between 6 and 10 mo. of age. Copyright © 1968. American Society of Animal Science . Copyright 1968 by American Society of Animal Science

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