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Seasonal changes in reproductive and pelage status during the initial ‘quiescent’ and first ‘active’ breeding seasons of the peripubertal pony colt

Published online by Cambridge University Press:  18 August 2016

C. McG. Argo ,
M.G. R. Collingsworth  and
J. E. Cox
C. McG. Argo
Affiliation:
School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
M.G. R. Collingsworth
Affiliation:
School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
J. E. Cox
Affiliation:
Department of Veterinary Clinical Sciences and Animal Husbandry, University of Liverpool, Leahurst, Neston CH64 7TE, UK
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Abstract

Pony colts (~12 m) are generally infertile during the breeding season of mature stallions. The mechanism which ‘delays’ puberty beyond the first potential breeding opportunity has not been described. Four pre- and four post-pubertal colts were monitored from November for 13 (group 1, 6 to 19 months of age) and 9 months (group 2, 18 to 27 months of age). Fortnightly, 15 blood samples were collected at hourly intervals from each colt to determine concentrations of prolactin (PRL), LH, FSH and testosterone (T). Testicular biopsies were collected monthly to evaluate spermatogenic activity. Puberty occurred between 17 and 19 months, and at the onset of the 2-year-old breeding season, all colts were fertile. Seasonal changes in the concentrations of all four hormones were observed in both groups. Prolactin concentrations were correlated with changes in day length (r = 0·88) in both groups, but a biphasic profile was noted in group 1. Moulting of the winter coat was coincident with seasonally increased PRL concentrations (P < 0·001). Seasonal changes in FSH, LH and T concentrations were similarly timed between groups and levels were maximal in mid April, mid March and mid May, respectively. However, overall mean concentrations of LH and T in group 1 animals were only 0·33 and 0·22 of group 2 values (P < 0·001). Suppression of gonadal activity during the colts’ first ‘quiescent’ breeding season was associated with low concentrations of circulating LH. Appropriately timed changes in plasma PRL, FSH and T concentrations and pelage indicated that the photoperiodic mechanism was functional in the pre-pubertal colt but pituitary LH release may be blocked by immaturity or active suppression.

Keywords

coatcoltshormonespubertyseasonal variation
Type
Non-ruminant nutrition, behaviour and production
Information
Animal Science , Volume 72 , Issue 1 , February 2001 , pp. 55 - 64
Copyright
Copyright © British Society of Animal Science 2001

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References

Alexander, S. L. and Irvine, C. H. G. 1987. Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare. Journal of Endocrinology 114: 351–362.CrossRefGoogle ScholarPubMed
Allain, D., Ravault, J. P., Panaretto, B. A. and Rougeot, J. 1986. Effects of pinealectomy on photoperiodic control of hair follicle activity in the Limousine ram: possible relationship with plasma prolactin levels. Journal of Pineal Research 3: 25–32.CrossRefGoogle ScholarPubMed
Almahbobi, G., Papadopoulos, V., Carreau, S. and Silberzahn, P. 1988. Age-related morphological and functional changes in the Leydig cells of the horse. Biology of Reproduction 38: 653–665.CrossRefGoogle ScholarPubMed
Argo, C. McG., Cox, J. E. and Gray, J. L. 1991. Effect of oral melatonin treatment on the seasonal physiology of pony stallions. Journal of Reproduction and Fertility, Supplement 44: 115–125.Google ScholarPubMed
Besognet, B., Hansen, B. S. and Daels, P. F. 1995. Prolactin secretion during the transitional phase and the relationship to onset of reproductive season in mares. Biology of Reproduction, Monograph Series 1: 459–467.CrossRefGoogle Scholar
Clay, C. M., Squires, E. L., Amann, R. P. and Nett, T. M. 1988. Influences of season and artificial photoperiod on stallions: luteinizing hormone, follicle stimulating hormone and testosterone. Journal of Animal Science 66: 1246–1255.CrossRefGoogle ScholarPubMed
Clay, C. M., Squires, E. L., Amann, R. P. and Pickett, B. W. 1987. Influence of season and artificial photoperiod on stallions: testicular size, seminal characteristics and sexual behaviour. Journal of Animal Science 64: 517–525.CrossRefGoogle Scholar
Cox, J. E. and Argo, C. McG. 1995. Effect of morphine and naloxone on plasma testosterone concentrations in Welsh Mountain pony stallions maintained under artificial photoperiod. Biology of Reproduction, Monograph Series 1: 609–614.CrossRefGoogle Scholar
Cox, J. L., Redhead, P. and Jawad, N. N. A. 1980. The effect of artificial photoperiod at the end of the breeding season on plasma testosterone concentrations in stallions. Australian Veterinary Journal 65: 239–241.CrossRefGoogle Scholar
Curlewis, J. D. 1992. Seasonal prolactin secretion and its role in seasonal reproduction: a review. Reproduction, Fertility and Development 4: 1–23.CrossRefGoogle ScholarPubMed
Evans, J. W., Stanfield, J., Hoffman, L. S. and Slaussen, C. 1987. Relationship of age and season and consumption of Senecio vulgaris to LH/hCG receptors in the stallion testis. Journal of Reproduction and Fertility 35: 56–65.Google Scholar
Evans, M. J., Alexander, S. L., Irvine, C. H. G., Livesey, J. H. and Donald, R. A. 1991. In vitro and in vivo studies of equine prolactin secretion throughout the year. Journal of Reproduction and Fertility, Supplement Series 44: 27–35.Google ScholarPubMed
Evans, M. J. and Irvine, C. H. G. 1976. Measurement of equine follicle stimulating hormone and luteinizing hormone: response of anoestrous mares to gonadotrophin releasing hormone. Biology of Reproduction 15: 477–484.CrossRefGoogle Scholar
Fitzgerald, B. P., Affleck, K. J., Barrows, S. P., Murdoch, W. L., Barker, K. B. and Loy, R. G. 1987. Changes in LH pulse frequency and amplitude in intact mares during the transition into the breeding season. Journal of Reproduction and Fertility 79: 485–493.CrossRefGoogle ScholarPubMed
Foster, D. L. and Olster, D. H. 1985. Effect of restricted nutrition on puberty in the lamb: patterns of tonic luteinizing hormone (LH) secretion and competency of the LH surge system. Endocrinology 116: 375–381.CrossRefGoogle ScholarPubMed
Freedman, I. J., Garcia, M. C. and Ginther, O. J. 1979. Influence of photoperiod and ovaries on seasonal reproductive activity in mares. Biology of Reproduction 20: 567–574.CrossRefGoogle ScholarPubMed
Ginther, O. J. 1979. Reproductive biology of the mare. Cross Plains, WI.Google Scholar
Holyoak, G. R., Little, T. V., Vernon, M., McCollum, W. H. and Timoney, P. J. 1994. Correlation between ultrasonographic findings and serum testosterone concentration in prepubertal and peripubertal colts. American Journal of Veterinary Research 55: 450–457.CrossRefGoogle ScholarPubMed
Irvine, C. H. G. and Alexander, S. L. 1982. Importance of testicular hormones in maintaining the annual pattern of LH secretion in the male horse. Journal of Reproduction and Fertility, Supplement 32: 97–102.Google ScholarPubMed
Irvine, C. H. G., Alexander, S. L. and Turner, J. E. 1986. Seasonal variation in the feedback of sex steroid hormones on LH concentrations in the male horse. Journal of Reproduction and Fertility 76: 221–230.CrossRefGoogle ScholarPubMed
Johnsen, S. G. 1970. Testicular biopsy score count — a method for registration of spermatogenesis in the human testes: normal values and results in 355 hypogonadal males. Hormones 1: 2–25.Google Scholar
Johnson, A. L. 1987. Seasonal and photo-induced changes in serum prolactin and pituitary reponsiveness to thyrotropin-releasing hormone in the mare. Proceedings of the Society for Experimental Biology and Medicine 184: 118–125.CrossRefGoogle Scholar
Johnson, L. and Neaves, W. B. 1981. Age-related changes in the Leydig cell population, seminiferous tubules and sperm production in stallions. Biology of Reproduction 29: 777–789.CrossRefGoogle Scholar
Johnson, L. and Thompson, D. L. 1983. Age related and seasonal variation in the Sertoli cell population, daily sperm production and serum concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone in stallions. Biology of Reproduction 29: 777–789.CrossRefGoogle ScholarPubMed
Johnson, L., Varner, D. D. and Thompson, D. L. 1991. Effect of age and season on the establishment of spermatogenesis in the horse. Journal of Reproduction and Fertility, Supplement 44: 87–97.Google ScholarPubMed
Kirk, R. E. 1982. Experimental design: procedures for the behavioural sciences, second edition. Brooks/Cole Publishing Co., New York.Google Scholar
Klingel, H. 1982. Social organization of feral horses. Journal of Reproduction and Fertility, Supplement 32: 89–95.Google ScholarPubMed
Lincoln, G. A. and Clarke, I. J. 1995. Evidence that melatonin acts in the pituitary gland through a dopamine-independent mechanism to mediate effects of daylength on the secretion of prolactin in the ram. Journal of Neuroendocrinology 7: 637–643.CrossRefGoogle ScholarPubMed
Lincoln, G. A. and Short, R. V. 1981. Seasonal breeding: nature’s contraceptive. Recent Progress in Hormone Research 36: 1–52.Google Scholar
Martinet, L., Allain, D. and Weiner, C. 1984. Role of prolactin in the photoperiodic control of moulting in the mink (Mustela vison). Journal of Endocrinology 103: 9–15.CrossRefGoogle ScholarPubMed
Naden, J., Amman, R. P. and Squires, E. L. 1990. Testicular growth, hormone concentrations, seminal characteristics and sexual behaviour in stallions. Journal of Reproduction and Fertility 88: 167–176.CrossRefGoogle ScholarPubMed
Pickett, B. W., Faulkner, L. C., Seidel, G. E., Berndtson, W. E. and Voss, J. L. 1976. Reproductive physiology of the stallion. VI. Seminal and behavioural characteristics. Journal of Animal Science 43: 617–625.CrossRefGoogle Scholar
Skinner, J. D. and Bowen, J. 1968. Puberty in the Welsh stallion. Journal of Reproduction and Fertility 16: 123–133.CrossRefGoogle ScholarPubMed
Thompson, D. L. and DePew, C. L. 1997. Prolactin, gonadotrophin and hair-shedding responses to daily sulpiride administration to geldings in winter. Journal of Animal Science 75: 1087–1091.CrossRefGoogle ScholarPubMed
Thompson, D. L., Hoffman, R. and DePew, C. L. 1997. Prolactin administration to seasonally anoestrous mares: reproductive, metabolic and hair-shedding responses. Journal of Animal Science 75: 1092–1099.CrossRefGoogle Scholar
Thompson, D. L., Pickett, B. W., Bernston, W. E., Voss, J. L. and Nett, T. M. 1979. Effect of testosterone and estradiol-17b alone and in combination on LH and FSH concentrations in blood serum and pituitaries of geldings and in serum after administration of GnRH. Biology of Reproduction 21: 1231–1237.CrossRefGoogle Scholar
Wesson, J. A. and Ginther, O. J. 1980. Plasma gonadotrophin concentrations in intact female and intact and castrated male prepubertal ponies. Biology of Reproduction 22: 541–549.CrossRefGoogle ScholarPubMed
Wesson, J. A. and Ginther, O. J. 1981a. Puberty in the female pony: reproductive behaviour, ovulation and plasma gonadotrophin concentrations. Biology of Reproduction 24: 977–986.CrossRefGoogle Scholar
Wesson, J. A. and Ginther, O. J. 1981b. Puberty in the male pony: plasma gonadotrophin concentrations and the effects of castration. Animal Reproduction Science 4: 165–175.CrossRefGoogle Scholar