Gonadotrophic Hormone Content of Swine Pituitary Glands in Relation to Age

Abstract
Pituitary glands of 26 Hampshire and 20 Duroc females varying in age from 1 to 1330 days and including cycling and pregnant animals, were assayed for gonadotrophic hormone content. The results were correlated with age and body weight. No significant difference in hormone potency was found between breed means of open sows. The unity potency of gonadotrophic hormone decreased linearly with increasing age (P<.01). Total potency for open sows showed no difference in breed means and increased linearly with age (P<.01). The amount of available hormone per unit of body weight was very high in day old females, decreased rapidly to about 225 days when first heats and ovulations occurred, and thereafter remained constant through 1330 days of age. Contrary to current assumption, onset of puberty coincides with the lowest titer of available gonadotrophic hormone. The theory is advanced that the high potency of glands from young animals is caused by a high rate of FSH secretion. Gradually the FSH/LH ratio of the complex becomes adjusted and when the proper ratio is reached cyclic ovarian function begins at puberty between 225 and 300 days. The low gonadotrophic potency of the pituitary gland is retained throughout the remainder of the reproductive life of the females (up to 1300 days of age included in this study). In pregnant sows there is a significant (P=.05) difference in gonadotrophic hormone potency between breeds, the Hampshires giving an 11.6 mg. greater chick testes weight. While the decrease in total gonadotrophic hormone potency with increasing length of pregnancy could not be shown to be statistically significant, the downward trend was similar in both breeds (Hampshires, b=.22; and Durocs, b=.12). Correlations between litter size and total pituitary potency of gonadotrophic hormone showed a definite breed difference (Hampshires, b=0; Duroc, b=1.94; P<.05). This difference may be due to differences in the age of females compared, rather than to a real breed difference. The correlation between pituitary gland potencies for gonadotrophic and thyrotrophic hormones was positive and highly significant (p<.01). Copyright © . .

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