PMID: 6962908Jan 1, 1982Paper

Importance of testicular hormones in maintaining the annual pattern of LH secretion in the male horse

Journal of Reproduction and Fertility. Supplement
C H Irvine, S L Alexander

Abstract

Serum LH was measured by radioimmunoassay in 5 long-term (greater than or equal to 3 years) castrated male horses bled at 30-min intervals for 2 h twice a month from March to February. There was no significant effect of month on LH levels; however, mean levels were significantly lower in spring than autumn (P less than 0.05). By contrast, stallions in the same environment showed a markedly seasonal pattern of LH secretion, with LH rising at the onset of the breeding season to reach levels in late spring 3-4 times those in early winter. Despite differences in seasonal patterns of secretion, annual mean LH levels in geldings (19.6 ng/ml) and stallions (20.4 ng/ml) were similar. In mid-summer, LH was measured in 6 geldings castrated 4-6 weeks previously, 25 geldings castrated 3-25 years previously, and 8 stallions; mean +/- s.e.m. LH values were 62.2 +/- 8.0, 14.0 +/- 1.6, and 13.0 +/- 2.2 ng/ml respectively. In the long-term geldings, LH was not affected by age, indicating that, after the rapid 4-fold post-castration rise, LH falls to within the normal range of pre-castration values and stabilizes. These results show that testicular hormones are necessary to maintain the normal seasonal pattern of LH secretion in the male horse, ...Continue Reading

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