The pituitary and testicular responses to GnRH challenge between 4 and 14 months of age in thoroughbred colts born in spring and autumn
Gonadotropin releasing-hormone analogue (buserelin) challenges were carried out every 8 weeks from 4 to 14 months of age on thoroughbred colts born in the spring ( n = 6) or autumn ( n = 5) to define the onset of puberty. In all colts, luteinizing hormone (LH) secretion followed a seasonal pattern,...
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Veröffentlicht in: | Animal reproduction science 2005-09, Vol.88 (3), p.287-298 |
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Sprache: | eng |
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Zusammenfassung: | Gonadotropin releasing-hormone analogue (buserelin) challenges were carried out every 8 weeks from 4 to 14 months of age on thoroughbred colts born in the spring (
n
=
6) or autumn (
n
=
5) to define the onset of puberty. In all colts, luteinizing hormone (LH) secretion followed a seasonal pattern, with high baseline and maximal concentrations in the spring and summer and low concentrations in the winter. Testosterone concentrations were undetectable before spring and, thus, autumn-born colts were younger than spring-born colts when a testosterone response to buserelin was first observed. Mean weights of the autumn-born colts were 300
kg (282–327
kg) at the time of the first detectable testosterone response in the following spring (October). Spring-born colts had reached this weight in the winter (May and June, before day length had increased) but did not exhibit a significant testosterone response until the spring at a mean weight of 352
kg (327–403
kg). It is proposed that colts must achieve a threshold body weight concurrently with stimulatory photoperiod for onset of puberty to occur. |
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ISSN: | 0378-4320 1873-2232 |
DOI: | 10.1016/j.anireprosci.2004.12.008 |