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Annual Changes in Day-length, Temperature, and Circulating Reproductive Hormones in Thoroughbred Stallions and Geldings.
Abstract: Changes in follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, immunoreactive(ir)-inhibin, testosterone, estradiol-17β, and insulin-like growth factor (IGF)-I in Thoroughbred stallions along with changes in prolactin secretion in geldings were studied. The correlations of day-length with changes in the concentrations of these hormones were also studied. Five stallions and thirteen geldings were employed to draw blood samples in monthly basis and radioimmunoassay was performed to measure these hormones. All hormones showed a seasonal pattern, the levels being highest during the breeding season and lowest during the winter months. Most of the hormones were at their highest concentration during the month of April, the mid of spring in northern hemisphere. The concentration of circulating IGF-I also demonstrated seasonality, the peak lying on the month of April. The plasma concentration of prolactin also increased during the breeding season. This phenomenon was similar both in stallions and geldings although geldings had lower concentration than that of stallions. The changes in concentration of prolactin in stallions and geldings correlated more towards the day-length than towards the temperature. These results clearly indicate the seasonality of pituitary and gonadal hormones of Thoroughbred stallions, the activity being highest during the month of April and May of the breeding season.
Publication Date: 2011-07-20 PubMed ID: 24833985PubMed Central: PMC4013971DOI: 10.1294/jes.22.29Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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The research article examines the influence of annual changes in day-length and temperature on various reproductive hormones found in Thoroughbred stallions and geldings.
Objective of the Study
The research aimed to study changes in the levels of several reproductive hormones in Thoroughbred stallions and geldings. Additionally, the correlation of day-length with these hormonal level changes was also investigated.
Methodology
- Eighteen horses, comprised of five stallions and thirteen geldings, were used in the study.
- Monthly blood samples were collected from each horse to study the hormonal changes over time.
- Specific hormones were targeted for measurement, including FSH, LH, prolactin, ir-inhibin, testosterone, estradiol-17β, and IGF-I.
- Radioimmunoassay, a technique used to measure the levels of these hormones in the blood, was employed.
Findings
- Seasonal patterns were observed in all the measured hormones, with the highest levels recorded during the breeding season and the lowest levels during the winter months.
- Most hormones peaked in April, which corresponds to the middle of spring in the northern hemisphere.
- IGF-I levels reflected the same seasonal pattern, reaching a peak in April.
- Prolactin levels also increased during the breeding season in both stallions and geldings, though levels were lower in the latter.
- The concentration changes in prolactin seemed to correlate more closely with changes in day-length than with changes in temperature.
Conclusion
The study found a clear seasonality in the activity of pituitary and gonadal hormones in Thoroughbred stallions. The highest activity was observed in April and May during the breeding season, with changes in prolactin concentration showing a stronger correlation with day-length than temperature.
Cite This Article
APA
Dhakal P, Tsunoda N, Nakai R, Kitaura T, Harada T, Ito M, Nagaoka K, Toishi Y, Taniyama H, Gen W, Taya K.
(2011).
Annual Changes in Day-length, Temperature, and Circulating Reproductive Hormones in Thoroughbred Stallions and Geldings.
J Equine Sci, 22(2), 29-36.
https://doi.org/10.1294/jes.22.29 Publication
Researcher Affiliations
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Shadai Corporation, Hokkaido 059-1432, Japan.
- Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Faculty of Veterinary Medicine, Department of Veterinary Pathology, Rakuno Gakuen University, Hokkaido 069-8501, Japan.
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan ; Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
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Citations
This article has been cited 12 times.- Ishimaru M, Matsui A, Seki K, Korosue K, Akiyama K, Mizukami H, Yoshida T, Taya K. Effects of different winter climates in Japan on body composition of young Thoroughbreds in training. J Vet Med Sci 2022 Nov 18;84(12):1585-1594.
- Kitaura T, Sato F, Hada T, Ishimaru M, Kodama R, Nambo Y, Watanabe G, Taya K. Influence of exercise and emotional stresses on secretion of prolactin and growth hormone in Thoroughbred horses. J Equine Sci 2021 Jun;32(2):49-53.
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