FREE SHIPPING over $40
OVER 9000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Home / Equine Research Bank / J Vet Med Sci / Effect of birth month on endocrine function in Thoroughbred ...
The Journal of veterinary medical science2025; 87(7); 804-815; doi: 10.1292/jvms.25-0061

Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan.

Abstract: Thoroughbreds born early in the year are believed to have an advantage in racing. However, the development of endocrine functions in early-born foals in the cold winter climate is unclear. The present study was conducted to elucidate the effect of birth month on the development of endocrine function in Thoroughbred foals born from February to May in Hokkaido by comparing hypothalamic-pituitary axis, adrenal and thyroid functions from birth to 24 weeks of age. Eighty-seven Thoroughbred foals were used to compare the changes in circulating luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, cortisol, and thyroxine among four birth month groups for each sex. The present study revealed that as foals grow, the hypothalamic-pituitary axis develops, allowing them to secrete LH and FSH in response to prolonged day length from about 10 weeks of age, regardless of birth month for both sexes. In addition, the increase in prolactin concentrations from May to August suggests that postnatal foals may have the ability to respond to prolonged daylength immediately after birth, independent of growth. Furthermore, circulating cortisol and thyroxine in the foals at birth were elevated regardless of birth month, suggesting that adrenal and thyroid functions were fully activated for the rapid growth during late gestation and adaptation to the external environment that occurs early postnatal period. In early-born foals, these hormone concentrations were found to be within the normal range, indicating that development of foals were not affected by the harsh Hokkaido winter.
Get Full Text
Publication Date: 2025-05-23 PubMed ID: 40414721PubMed Central: PMC12246564DOI: 10.1292/jvms.25-0061Google 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.
LinkedInCopy
  • Journal Article

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.

Overview

  • This study investigated how the month of birth influences the hormonal development of Thoroughbred foals born in Hokkaido, Japan, focusing on endocrine functions from birth to 24 weeks of age.
  • It examined key hormones related to growth and adaptation to environmental factors, to understand whether early-born foals experience any endocrine disadvantages due to the cold winter climate.

Introduction and Purpose

  • Thoroughbred foals born earlier in the year are generally thought to have a competitive advantage in racing due to their advanced development.
  • Hokkaido, located in northern Japan, has a harsh cold winter climate that could potentially affect the foals’ physiological development, especially their endocrine function.
  • The research aimed to clarify how the month of birth (from February to May) affects the development of three major endocrine systems in foals: the hypothalamic-pituitary axis, adrenal function, and thyroid function.
  • Specifically, the study compared hormone levels related to these systems over the first 24 weeks of life in foals born at different times within this early-year window.

Methodology

  • The study population consisted of 87 Thoroughbred foals born in Hokkaido between February and May.
  • Foals were grouped based on their birth month to compare hormone changes over time.
  • Hormones measured included:
    • Luteinizing hormone (LH) and follicle-stimulating hormone (FSH): indicators of hypothalamic-pituitary axis activity.
    • Prolactin: associated with responses to day length and various physiological processes.
    • Cortisol: reflecting adrenal stress hormone activity.
    • Thyroxine (T4): representing thyroid function important for metabolism and growth.
  • Hormone measurements were performed at multiple time points from birth until 24 weeks of age.
  • Comparisons were made for each sex to determine whether hormonal development differed between males and females or based on birth month.

Key Findings

  • Hypothalamic-Pituitary Axis Development:
    • LH and FSH secretion increased in response to prolonged day lengths starting from about 10 weeks of age.
    • This response occurred similarly regardless of birth month or sex, indicating normal maturation of this axis during early postnatal life.
  • Prolactin Concentrations:
    • An increase in prolactin levels from May to August was observed, suggesting that foals can respond to changes in day length from a very early age.
    • This response was independent of physical growth, indicating an innate sensitivity to environmental light cues soon after birth.
  • Adrenal (Cortisol) and Thyroid (Thyroxine) Functions:
    • At birth, cortisol and thyroxine levels were elevated irrespective of the foal’s birth month.
    • This suggests that these endocrine systems are fully activated by late gestation to support rapid growth and to help the newborn adapt to the external environment.
    • These hormone levels were within normal ranges even in early-born foals, indicating that the cold Hokkaido winter did not negatively affect their adrenal and thyroid development.

Conclusions and Implications

  • Endocrine functions related to growth and environmental adaptation develop appropriately in Thoroughbred foals born from February to May in Hokkaido, despite the harsh winter conditions.
  • Early birth does not appear to compromise the hormonal development necessary for growth and maturation.
  • Foals show the ability to respond to environmental cues such as day length soon after birth, which is important for seasonal physiological regulation.
  • Findings support the idea that early-born foals can maintain normal endocrine function, potentially retaining the racing advantage previously attributed to their earlier birth date without endocrine disadvantage due to climate.

Cite This Article

APA
Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. (2025). Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci, 87(7), 804-815. https://doi.org/10.1292/jvms.25-0061

Publication

The Journal of veterinary medical science
ISSN: 1347-7439
NlmUniqueID: 9105360
Country: Japan
Language: English
Volume: 87
Issue: 7
Pages: 804-815

Researcher Affiliations

Ishimaru, Mutsuki
  • International Department, Japan Racing Association, Tokyo, Japan.
Kume, Koichi
  • Equine Department, Japan Racing Association, Tokyo, Japan.
Murase, Harutaka
  • Equine Department, Japan Racing Association, Tokyo, Japan.
Sato, Fumio
  • Japan Farriery Association, Tokyo, Japan.
Matsui, Akira
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido, Japan.
Ohmura, Hajime
  • Hidaka Training and Research Center, Japan Racing Association, Hokkaido, Japan.
Taya, Kazuyoshi
  • Laboratory of Veterinary Physiology, Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan.

MeSH Terms

  • Animals
  • Female
  • Male
  • Animals, Newborn / physiology
  • Follicle Stimulating Hormone / blood
  • Horses / physiology
  • Horses / growth & development
  • Horses / blood
  • Hydrocortisone / blood
  • Hypothalamo-Hypophyseal System / physiology
  • Japan
  • Luteinizing Hormone / blood
  • Prolactin / blood
  • Seasons
  • Thyroxine / blood

Conflict of Interest Statement

The authors declare no conflicts of interest associated with this manuscript.

References

This article includes 64 references
  1. Aleman M, McCue PM, Chigerwe M, Madigan JE. Plasma concentrations of steroid precursors, steroids, neuroactive steroids, and neurosteroids in healthy neonatal foals from birth to 7 days of age.. 33: 2286–2293.
    doi: 10.1111/jvim.15618pmc: PMC6766486pubmed: 31489708google scholar: lookup
  2. Alexander SL, Irvine CHG, Evans MJ. Inter-relationships between the secretory dynamics of thyrotrophin-releasing hormone, thyrotrophin and prolactin in periovulatory mares: effect of hypothyroidism.. 16: 906–915.
    doi: 10.1111/j.1365-2826.2004.01249.xpubmed: 15584931google scholar: lookup
  3. Arai KY, Watanabe G, Fujimoto M, Nagata S, Takemura Y, Taya K. A sensitive radioimmunoassay for cortisol using 125I-labeled radioligand.. 41: j15–j20.
    doi: 10.1262/jrd.95-415j15google scholar: lookup
  4. Arai KY, Tanaka Y, Taniyama H, Tsunoda N, Nambo Y, Nagamine N, Watanabe G, Taya K. Expression of inhibins, activins, insulin-like growth factor-I and steroidogenic enzymes in the equine placenta.. 31: 19–34.
    doi: 10.1016/j.domaniend.2005.09.005pubmed: 16233970google scholar: lookup
  5. Beythien E, Aurich C, Wulf M, Aurich J. Effects of season on placental, foetal and neonatal development in horses.. 97: 98–103.
    doi: 10.1016/j.theriogenology.2017.04.027pubmed: 28583616google scholar: lookup
  6. Breuhaus BA. Thyroid function and dysfunction in term and premature equine neonates.. 28: 1301–1309.
    doi: 10.1111/jvim.12382pmc: PMC4857961pubmed: 24934827google scholar: lookup
  7. Cymbaluk NF. Cold housing effects on growth and nutrient demand of young horses.. 68: 3152–3162.
    doi: 10.2527/1990.68103152xpubmed: 2254193google scholar: lookup
  8. Dhakal P, Tsunoda N, Nakai R, Nagaoka K, Nambo Y, Sato F, Taniyama H, Taya K. Post-natal dynamic changes in circulating follicle-stimulating hormone, luteinizing hormone, immnoreactive inhibin, progesterone, testosterone and estraduol-17 in Thoroughbred colts until 6 months of age.. 22: 9–15.
    doi: 10.1294/jes.22.9pmc: PMC4013995pubmed: 24833982google scholar: lookup
  9. Dhakal P, Tsunoda N, Nakai R, Kitaura T, Harada T, Ito M, Nagaoka K, Toishi Y, Taniyama H, Gen W, Taya K. Annual changes in day-length, temperature, and circulating reproductive hormones in Thoroughbred stallions.. 22: 29–36.
    doi: 10.1294/jes.22.29pmc: PMC4013971pubmed: 24833985google scholar: lookup
  10. Dhakal P, Hirama A, Nambo Y, Harada T, Sato F, Nagaoka K, Watanabe G, Taya K. Circulating pituitary and gonadal hormones in spring-born Thoroughbred fillies and colts from birth to puberty.. 58: 522–530.
    doi: 10.1262/jrd.2011-025pubmed: 22673032google scholar: lookup
  11. Equine Research Institute, Japan Racing Association. Japanese feeding standard for horses.. pp. 71–73.
  12. Forhead AJ, Curtis K, Kaptein E, Visser TJ, Fowden AL. Developmental control of iodothyronine deiodinases by cortisol in the ovine fetus and placenta near term.. 147: 5988–5994.
    doi: 10.1210/en.2006-0712pubmed: 16959839google scholar: lookup
  13. Fowden AL, Silver M. Comparative development of the pituitary-adrenal axis in the fetal foal and lamb.. 30: 170–177.
    doi: 10.1111/j.1439-0531.1995.tb00141.xgoogle scholar: lookup
  14. Fowden AL, Forhead AJ. Endocrine regulation of feto-placental growth.. 72: 257–265.
    pubmed: 19844111
  15. Fowden AL, Forhead AJ, Ousey JC. Endocrine adaptations in the foal over the perinatal period.. 41: 130–139.
    doi: 10.1111/j.2042-3306.2011.00505.xpubmed: 22594041google scholar: lookup
  16. Gold JR, Divers TJ, Barton MH, Lamb SV, Place NJ, Mohammed HO, Bain FT. Plasma adrenocorticotropin, cortisol, and adrenocorticotropin/cortisol ratios in septic and normal-term foals.. 2007;21:791–796.
    pubmed: 17708401
  17. Holtby AR, McGivney BA, Browne JA, Katz LM, Murphy KJ, Hill EW. Variation in salivary cortisol responses in yearling Thoroughbred racehorses during their first year of training.. PLOS ONE 2023;18:e0284102.
    doi: 10.1371/journal.pone.0284102pmc: PMC10079128pubmed: 37023093google scholar: lookup
  18. Irvine CH, Evans MJ. Postnatal changes in total and free thyroxine and triiodothyronine in foal serum.. 1975;23:709–715.
    pubmed: 1060870
  19. 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.. 2022;84:1585–1594.
    doi: 10.1292/jvms.22-0378pmc: PMC9791233pubmed: 36244743google scholar: lookup
  20. 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.. 2024;86:756–768.
    doi: 10.1292/jvms.24-0083pmc: PMC11251821pubmed: 38777756google scholar: lookup
  21. Jaroenporn S, Nagaoka K, Kasahara C, Ohta R, Watanabe G, Taya K. Physiological roles of prolactin in the adrenocortical response to acute restraint stress.. 2007;54:703–711.
    doi: 10.1507/endocrj.K07-003pubmed: 17785918google scholar: lookup
  22. Jaroenporn S, Nagaoka K, Ohta R, Watanabe G, Taya K. Direct effects of prolactin on adrenal steroid release in male Hatano high-avoidance (HAA) rats may be mediated through Janus kinase 2 (Jak2) activity.. 2007;53:887–893.
    doi: 10.1262/jrd.18174pubmed: 17519522google scholar: lookup
  23. Jaroenporn S, Furuta C, Nagaoka K, Watanabe G, Taya K. Comparative effects of prolactin versus ACTH, estradiol, progesterone, testosterone, and dihydrotestosterone on cortisol release and proliferation of the adrenocortical carcinoma cell line H295R.. 2008;33:205–209.
    doi: 10.1007/s12020-008-9075-9pubmed: 18484195google scholar: lookup
  24. Jaroenporn S, Nagaoka K, Ohta R, Shirota M, Watanabe G, Taya K. Differences in adrenocortical secretory and gene expression responses to stimulation in vitro by ACTH or prolactin between high- and low-avoidance Hatano rats.. 2009;12:22–29.
    doi: 10.1080/10253890801976652pubmed: 18609294google scholar: lookup
  25. Jaroenporn S, Nagaoka K, Ohta R, Watanabe G, Taya K. Prolactin induces phosphorylation of the STAT5 in adrenal glands of Hatano rats during stress.. 2009;85:172–177.
    doi: 10.1016/j.lfs.2009.05.011pubmed: 19481553google scholar: lookup
  26. Johnson AL. Serum concentrations of prolactin, thyroxine and triiodothyronine relative to season and the estrous cycle in the mare.. 1986;62:1012–1020.
    doi: 10.2527/jas1986.6241012xpubmed: 3086267google scholar: lookup
  27. Johnson AL. Seasonal and photoperiod-induced changes in serum prolactin and pituitary responsiveness to thyrotropin-releasing hormone in the mare.. 1987;184:118–122.
    doi: 10.3181/00379727-184-42455pubmed: 3099304google scholar: lookup
  28. Johnson AL, Becker SE. Effects of physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare.. 1987;65:1292–1297.
    doi: 10.2527/jas1987.6551292xpubmed: 3121569google scholar: lookup
  29. Jones L, Hollands T. Estimation of growth rates in UK Thoroughbreds.. 2005;21:121–123.
  30. Kaneko H, Noguchi J, Kikuchi K, Akagi S, Shimada A, Taya K, Watanabe G, Hasegawa Y. Production and endocrine role of inhibin during the early development of bull calves.. 2001;65:209–215.
    doi: 10.1095/biolreprod65.1.209pubmed: 11420242google scholar: lookup
  31. 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. 2021;32:49–53.
    doi: 10.1294/jes.32.49pmc: PMC8240521pubmed: 34220271google scholar: lookup
  32. 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. 2015;26:57–66.
    doi: 10.1294/jes.26.57pmc: PMC4496423pubmed: 26170762google scholar: lookup
  33. Liggins GC. The role of cortisol in preparing the fetus for birth. 1994;6:141–150.
    doi: 10.1071/RD9940141pubmed: 7991781google scholar: lookup
  34. Matsui A, Inoue Y, Asai Y, Yamanobe A. Effect of the geographic breeding region on digestible energy intake and growth rate of Thoroughbred yearling horses: a comparison of the Hidaka and Miyazaki regions of Japan. 2005;16:19–26.
    doi: 10.1294/jes.16.19google scholar: lookup
  35. 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. 2015;26:49–56.
    doi: 10.1294/jes.26.49pmc: PMC4496422pubmed: 26170761google scholar: lookup
  36. Morreale de Escobar G, Obregon MJ, Escobar del Rey F. Role of thyroid hormone during early brain development. 2004;151 Suppl 3:U25–U37.
    doi: 10.1530/eje.0.151u025pubmed: 15554884google scholar: lookup
  37. Murray MJ, Luba NK. Plasma gastrin and somatostatin, and serum thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and cortisol concentrations in foals from birth to 28 days of age. 1993;25:237–239.
    doi: 10.1111/j.2042-3306.1993.tb02951.xpubmed: 8099543google scholar: lookup
  38. Nagy P, Guillaume D, Daels P. Seasonality in mares. 2000;60–61:245–262.
    doi: 10.1016/S0378-4320(00)00133-0pubmed: 10844199google scholar: lookup
  39. Nakada K, Moriyoshi M, Nakao T, Watanabe G, Taya K. Changes in concentrations of plasma immunoreactive follicle-stimulating hormone, luteinizing hormone, estradiol-17beta, testosterone, progesterone, and inhibin in heifers from birth to puberty. 2000;18:57–69.
    doi: 10.1016/S0739-7240(99)00063-6pubmed: 10701764google scholar: lookup
  40. Nakada K, Isikawa Y, Nakao T, Sawamukai Y. Changes in responses to GnRH on luteinizing hormone and follicle stimulating hormone secretion in prepubertal heifers. 2002;48:545–551.
    doi: 10.1262/jrd.48.545google scholar: lookup
  41. Nakai R, Weng Q, Tanaka Y, Tsunoda N, Taniyama H, Haramaki S, Nambo Y, Watanabe G, Taya K. Change in circulating follicle-stimulating hormone, luteinizing hormone, immunoreactive inhibin, progesterone, testosterone and estradiol-17b in fillies from birth to 6 months of age. 2007;18:85–91.
    doi: 10.1294/jes.18.85pmc: PMC4013995pubmed: 24833982google scholar: lookup
  42. Nathanielsz PW, Rossdale PD, Silver M, Comline RS. Studies on fetal, neonatal and maternal cortisol metabolism in the mare. 1975;23:625–630.
    pubmed: 1060854
  43. Nolan MB, Walsh CM, Duff N, McCrarren C, Prendergast RL, Murphy BA. Artificially extended photoperiod administered to pre-partum mares via blue light to a single eye: observations on gestation length, foal birth weight and foal hair coat at birth. 2017;100:126–133.
    doi: 10.1016/j.theriogenology.2017.06.012pubmed: 28708527google scholar: lookup
  44. Ousey JC, Forhead AJ, Rossdale PD, Grainger L, Houghton E, Fowden AL. Ontogeny of uteroplacental progestagen production in pregnant mares during the second half of gestation. 2003;69:540–548.
    doi: 10.1095/biolreprod.102.013292pubmed: 12700198google scholar: lookup
  45. Pagan JD. A summary of growth rates of Thoroughbred horses in Kentucky. 1998:pp. 449–456.
  46. Pagan JD, Brown-Douglas CG, Caddel S. Body weight and condition of Kentucky Thoroughbred mares and their foals as influenced by month of foaling, season, and gender. 2009:pp. 137–145.
  47. Pruessner JC, Kirschbaum C, Meinlschmid G, Hellhammer DH. Two formulas for computation of the area under the curve represent measures of total hormone concentration versus time-dependent change. 2003;28:916–931.
    doi: 10.1016/S0306-4530(02)00108-7pubmed: 12892658google scholar: lookup
  48. Raeside JI, Renaud RL, Christie HL. Postnatal decline in gonadal secretion of dehydroepiandrosterone and 3 beta-hydroxyandrosta-5,7-dien-17-one in the newborn foal. 1997;155:277–282.
    doi: 10.1677/joe.0.1550277pubmed: 9415062google scholar: lookup
  49. Silver M, Fowden AL, Knox J, Ousey J, Cash R, Rossdale PD. Relationship between circulating tri-iodothyronine and cortisol in the perinatal period in the foal. 1991;44:619–626.
    pubmed: 1665521
  50. Silvia PJ, Squires EL, Nett TM. Pituitary responsiveness of mares challenged with GnRH at various stages of the transition into the breeding season. 1987;64:790–796.
    doi: 10.2527/jas1987.643790xpubmed: 3106292google scholar: lookup
  51. Tanaka Y, Taniyama H, Tsunoda N, Shinbo H, Nagamine N, Nambo Y, Nagata S, Watanabe G, Herath CB, Groome NP, Taya K. The testis as a major source of circulating inhibins in the male equine fetus during the second half of gestation. 2002;23:229–236.
    doi: 10.1002/j.1939-4640.2002.tb02619.xpubmed: 11868816google scholar: lookup
  52. Taya K. Stress and prolactin. 2011;18:275–283.
  53. The Japan Bloodhorse Breeder’s Association, Japan Association for International Racing and Stud Book. Bloodhorse statistics 2024. 2024;56–57.
  54. Thompson DL Jr, Oberhaus EL. Prolactin in the horse: historical perspective, actions and reactions, and its role in reproduction. 2015;35:343–353.
    doi: 10.1016/j.jevs.2015.03.199google scholar: lookup
  55. Thompson DL Jr, DePew CL, Ortiz A, Sticker LS, Rahmanian MS. Growth hormone and prolactin concentrations in plasma of horses: sex differences and the effects of acute exercise and administration of growth hormone-releasing hormone. 1994;72:2911–2918.
    doi: 10.2527/1994.72112911xpubmed: 7730185google scholar: lookup
  56. Tohei A, Akai M, Tomabechi T, Mamada M, Taya K. Adrenal and gonadal function in hypothyroid adult male rats. 1997;152:147–154.
    doi: 10.1677/joe.0.1520147pubmed: 9014850google scholar: lookup
  57. Tohei A, Watanabe G, Taya K. Hypersecretion of corticotrophin-releasing hormone and arginine vasopressin in hypothyroid male rats as estimated with push-pull perfusion. 1998;156:395–400.
    doi: 10.1677/joe.0.1560395pubmed: 9518888google scholar: lookup
  58. Tohei A, Watanabe G, Taya K. Effects of thyroidectomy or thiouracil treatment on copulatory behavior in adult male rats. 1998;60:281–285.
    doi: 10.1292/jvms.60.281pubmed: 9560772google scholar: lookup
  59. Tohei A, Imai A, Watanabe G, Taya K. Influence of thiouracil-induced hypothyroidism on adrenal and gonadal functions in adult female rats. 1998;60:439–446.
    doi: 10.1292/jvms.60.439pubmed: 9592715google scholar: lookup
  60. Tohei A, Taya K, Watanabe G, Voogt JL. Hypothyroidism increases prolactin secretion and decreases the intromission threshold for induction of pseudopregnancy in adult female rats. 2000;69:391–397.
    doi: 10.1016/S0031-9384(00)00224-9pubmed: 10913776google scholar: lookup
  61. Tsukamura H. Kobayashi Award 2019: the neuroendocrine regulation of the mammalian reproduction. 2022;315:113755.
    doi: 10.1016/j.ygcen.2021.113755pubmed: 33711315google scholar: lookup
  62. Walsh CM, Prendergast RL, Sheridan JT, Murphy BA. Blue light from light-emitting diodes directed at a single eye elicits a dose-dependent suppression of melatonin in horses. 2013;196:231–235.
    doi: 10.1016/j.tvjl.2012.09.003pubmed: 23079244google scholar: lookup
  63. Wesson JA, Miller KF, Ginther OJ. Response of plasma LH and FSH to gonadotropin-releasing hormone in pony foals and ovariectomized pony mares. 1980;14:113–121.
    doi: 10.1016/0093-691X(80)90098-9pubmed: 16725517google scholar: lookup
  64. Yamamoto S, Asai Y, Kusunose R. Effects of sex, birth month, parity, weight of dam and farm on the growth of Thoroughbred foals and yearlings. 1993;64:491–498.

Citations

This article has been cited 0 times.
Subscribe to our newsletter
Join 99,005 horse owners like you who receive our email updates on horse health and nutrition.