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Relationship between thyroid function and seasonal reproductive activity in mares.
G Huszenicza1, P Nagy, J Juhász
1University of Veterinary Science, István u. 2., 1078, Budapest, Hungary.
Journal of Reproduction and Fertility. Supplement
|August 5, 2010
Summary
Thyroid hormones triiodothyronine and thyroxine are lower in anestrous mares during the non-breeding season. These changes may be influenced by hypothalamic control, not direct thyroid gland involvement in equine seasonality.
Area of Science:
- Reproductive Endocrinology
- Equine Physiology
- Thyroid Function
Background:
- Seasonal reproductive activity in mares is influenced by environmental factors.
- The role of thyroid hormones in equine reproductive seasonality requires further investigation.
Purpose of the Study:
- To investigate the relationship between thyroid function and seasonal reproductive activity in mares.
- To compare plasma triiodothyronine and thyroxine concentrations in anestrous and cyclic mares during the anovulatory season.
Main Methods:
- Plasma concentrations of triiodothyronine and thyroxine were measured in anestrous and cyclic mares.
- Hormone levels were monitored in mares that foaled before the vernal equinox.
- Thyroid hormone concentrations were assessed in adult and young mares.
Main Results:
- Significantly higher thyroxine concentrations were observed in cyclic mares compared to anestrous mares.
- Lower plasma triiodothyronine and thyroxine concentrations were found in anestrous mares post-foaling and during the anovulatory period.
- Increases in thyroid hormones correlated with the first ovulation post-parturition.
Conclusions:
- Decreased thyroid hormone concentrations in anestrous mares may be a result of hypothalamic control, not direct thyroid gland regulation of seasonality.
- Thyroid function does not appear to be the primary driver of seasonal reproductive activity in horses.
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