Circulating pituitary and gonadal hormones in spring-born Thoroughbred fillies and colts from birth to puberty.
Abstract: The present study was conducted to elucidate the profile of circulating gonadotropins and gonadal hormones from birth to puberty and relationship between gonadal seasonality and hormonal secretion in both sexes of Thoroughbred horses. Spring-born colts (n=6) and fillies (n=9) were blood sampled weekly from jugular vein from birth to 60 weeks of age. Circulating FSH, LH, prolactin, testosterone, progesterone, estradiol-17β, and immunoreactive (ir)-inhibin were measured by radioimmunoassay. In both sexes, the steroid hormones levels were remarkably high at birth, rapidly dropped within a week and remained at the lower levels until the start of second spring after birth. Ir-inhibin was also high during the birth, remaining lowest during winter and again increasing towards the second summer. There was an increase in FSH concentration in foals during the first summer months after birth and in the next summer, the FSH concentration along with that of LH increased significantly. The seasonal increase in circulating prolactin was remarkable even in the first year, and no differences were noted between the two summers. These results clearly demonstrated that the hypothalamo-pituitary axis is already responsive to changes in photoperiod and secrete prolactin similar to adult horses, but pituitary gonadotrophs for FSH and LH secretion is less sensitive. When the values of these hormones in the second breeding season after birth were compared with adult values of the respective sex in the breeding season, no significant differences were observed, indicating that spring-born fillies and colts have already attained the stage of puberty at the second breeding season after birth.
Publication Date: 2012-05-19 PubMed ID: 22673032DOI: 10.1262/jrd.2011-025Google 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
- Research Support
- Non-U.S. Gov't
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
The research focuses on understanding the hormonal fluctuations in Thoroughbred fillies and colts from their birth to puberty. The researchers analyze the hormonal secretion patterns of both sexes and their links to gonadal seasonality.
Research Methodology
- The researchers conducted the study on spring-born Thoroughbred colts (6 in number) and fillies (9 in number).
- They collected blood samples from the jugular vein on a weekly basis from birth until they reached 60 weeks of age.
- They measured circulating FSH, LH, prolactin, testosterone, progesterone, estradiol-17β, and immunoreactive (ir)-inhibin through radioimmunoassay.
Hormonal Secretions from Birth to Puberty
- They observed that the levels of steroid hormones in both the sexes were extraordinarily high at birth.
- These levels dropped significantly within a week, and maintained these lower levels up to the start of the second spring after birth.
- Similar to the steroid hormone pattern, ir-inhibin concentrations were also high during the birth, decreased to the lowest during winter, and again peaked towards the second summer.
- The following fluctuations in the FSH concentration were noted:
- FSH concentration in foals increased during the first summer months after birth.
- In the subsequent summer, a significant increase in both FSH and LH concentrations was observed.
- Among all the hormonal variations noticed, the increase in the level of prolactin was the most pronounced, even in the first year. No significant differences were noted between the two summers.
Hypothalamo-Pituitary Axis Responsiveness
- The study results displayed that the hypothalamo-pituitary axis of the foals was already responsive to changes in photoperiod and secreted prolactin similar to adult horses.
- However, their pituitary gonadotrophs, responsible for FSH and LH secretion, showed lower sensitivity to these changes.
Puberty in Spring-born Fillies and Colts
- When values of these hormones from the second breeding season following birth were compared with adult values of the same sex during the breeding season, no substantial differences were noticed.
- This suggests that by the second breeding season after birth, spring-born fillies and colts may have already achieved puberty.
Cite This Article
APA
Dhakal P, Hirama A, Nambo Y, Harada T, Sato F, Nagaoka K, Watanabe G, Taya K.
(2012).
Circulating pituitary and gonadal hormones in spring-born Thoroughbred fillies and colts from birth to puberty.
J Reprod Dev, 58(5), 522-530.
https://doi.org/10.1262/jrd.2011-025 Publication
Researcher Affiliations
- Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan.
MeSH Terms
- Animals
- Animals, Inbred Strains
- Animals, Newborn
- Estradiol / blood
- Female
- Follicle Stimulating Hormone / blood
- Gonadal Hormones / blood
- Horses / physiology
- Inhibins / blood
- Japan
- Luteinizing Hormone / blood
- Male
- Pituitary Hormones / blood
- Progesterone / blood
- Prolactin / blood
- Seasons
- Sex Characteristics
- Sexual Maturation
- Testosterone / blood
- Weight Gain
Citations
This article has been cited 12 times.- Boakari YL, Legacki E, Alonso MA, Dos Santos ACF, Nichi M, Conley AJ, Fernandes CB. Postnatal Dynamics of Circulating Steroid Hormones in Mule and Equine Neonates. Vet Sci 2022 Oct 28;9(11).
- Katsumata E, Jaroenporn S, Ueda Y, Arai K, Katsumata H, Watanabe G, Taya K. Circulating gonadotropins and testicular hormones during sexual maturation and annual changes in male bottlenose dolphins (Tursiops truncatus). J Vet Med Sci 2017 Nov 17;79(11):1899-1905.
- Toishi Y, Tsunoda N, Kume K, Nagaoka K, Watanabe G, Taya K. PATHFAST, a novel chemiluminescent enzyme immunoassay for measuring estradiol in equine whole blood and serum. J Reprod Dev 2016 Dec 20;62(6):631-634.
- Harada T, Nambo Y, Ishimaru M, Sato F, Nagaoka K, Watanabe G, Taya K. Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings. J Equine Sci 2015;26(4):147-50.
- Takahashi Y, Akai M, Murase H, Nambo Y. Seasonal changes in serum progesterone levels in Thoroughbred racehorses in training. J Equine Sci 2015;26(4):135-9.
- Suzuki T, Mizukami H, Nambo Y, Ishimaru M, Miyata K, Akiyama K, Korosue K, Naito H, Nagaoka K, Watanabe G, Taya K. Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions. J Equine Sci 2015;26(4):113-24.
- Kunii H, Nambo Y, Okano A, Matsui A, Ishimaru M, Asai Y, Sato F, Fujii K, Nagaoka K, Watanabe G, Taya K. Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies. J Equine Sci 2015;26(2):57-66.
- Mizukami H, Suzuki T, Nambo Y, Ishimaru M, Naito H, Korosue K, Akiyama K, Miyata K, Yamanobe A, Nagaoka K, Watanabe G, Taya K. Comparison of growth and endocrine changes in Thoroughbred colts and fillies reared under different climate conditions. J Equine Sci 2015;26(2):49-56.
- Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci 2025 Jul 7;87(7):804-815.
- Davies CS, Shearer CL, Greene LK, Mitchell J, Walsh D, Goerlich VC, Clutton-Brock TH, Drea CM. Androgen-mediated maternal effects and trade-offs: postnatal hormone development, growth, and survivorship in wild meerkats. Front Endocrinol (Lausanne) 2024;15:1418056.
- Ishimaru M, Tsuchiya T, Endo Y, Matsui A, Ohmura H, Murase H, Korosue K, Sato F, Taya K. Effects of different winter paddock management of Thoroughbred weanlings and yearlings in the cold region of Japan on physiological function, endocrine function and growth. J Vet Med Sci 2024 Jul 2;86(7):756-768.
- Ishimaru M, Okano A, Matsui A, Murase H, Korosue K, Akiyama K, Taya K. Effects of an extended photoperiod on body composition of young Thoroughbreds in training. J Vet Med Sci 2024 Jan 10;86(1):58-65.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
