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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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