Importance of testicular hormones in maintaining the annual pattern of LH secretion in the male horse.
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, including the increase in LH at the onset of the breeding season. It is suggested that the effects of testicular hormones on LH secretion include (1) a negative feedback at the hypothalamus/pituitary as observed in other species, and (2) a positive component in the pathway by which LH is increased at the onset of the breeding season.
Publication Date: 1982-01-01 PubMed ID: 6962908
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- Journal Article
Summary
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The research investigates the influence of testicular hormones in maintaining the normal LH secretion pattern in male horses, also showing that these hormones are necessary for the onset of the breeding season.
Overview of Research
- The study focused on the role of testicular hormones in the annual pattern of Luteinizing Hormone (LH) secretion in male horses. This secretion pattern plays a vital role in male horse reproductive cycles, particularly the breeding season.
- The researchers conducted blood tests on different groups of horses, including long-term castrated horses (geldings), recently castrated geldings, and intact male horses (stallions).
Findings
- No significant difference was observed in LH levels in geldings over different months. Yet, springtime LH levels were significantly lower compared to the autumn.
- Stallions, on the other hand, showed a clear seasonal pattern of LH secretion. Their LH levels rose at the onset of the breeding season, peaking in late spring at approximately 3-4 times the early winter levels.
- The average annual LH levels in geldings and stallions were roughly the same, at 19.6 ng/ml and 20.4 ng/ml, respectively.
- The study found LH levels in recently-castrated geldings to be significantly higher (62.2 ng/ml) than long-term geldings (14.0 ng/ml) and stallions (13.0 ng/ml).
- Long-term geldings’ LH levels did not vary with age. They initially experienced a swift four-fold increase in LH after castration, but levels then declined back to within the typical pre-castration range and stabilized.
Conclusion
- The researchers concluded that testicular hormones are critical for maintaining LH’s normal seasonal pattern in male horses, including the crucial increase at the breeding season’s commencement.
- They suggested that the effects of these hormones on LH secretion include negative feedback at the hypothalamus/pituitary, as found in other species, and a positive element in the pathway that boosts LH at the breeding season’s onset.
Cite This Article
APA
Irvine CH, Alexander S.
(1982).
Importance of testicular hormones in maintaining the annual pattern of LH secretion in the male horse.
J Reprod Fertil Suppl, 32, 97-102.
Publication
Researcher Affiliations
MeSH Terms
- Androgens / physiology
- Animals
- Castration
- Horses / physiology
- Luteinizing Hormone / metabolism
- Male
- Periodicity
- Radioimmunoassay
- Seasons
- Testis / physiology
Citations
This article has been cited 1 times.- Sheldon SA, Aleman M, Costa LRR, Santoyo AC, Weich KM, Howey Q, Madigan JE. Luteinizing hormone concentrations in healthy horses and horses with trigeminal-mediated headshaking over an 8-hour period. J Vet Intern Med 2019 Mar;33(2):885-888.
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