Thyroid function and pregnancy status in broodmares.

The research examined whether there is a correlation between thyroid function and the pregnancy status in broodmares, determining that decreased thyroid function is not a common cause for infertility and highlighting that the practice of treating broodmares with thyroid hormone to promote fertility is doubtful.

Introduction

A study was undertaken to establish if there existed any relationship between the function of the thyroid in broodmares and their pregnancy status. The subjects of the study were 79 Thoroughbred and Standardbred broodmares, aged between 2 and 22 years old.

Methodology

• The study was carried out prospectively. The researchers began their process by measuring the concentrations of serum triiodothyronine (T3) and thyroxine (T4) in the broodmares’ bodies.
• T3 and T4 levels were first measured under ordinary circumstances (baseline readings). Then, thyrotropin releasing hormone (TRH) was administered intravenously to the mares. Post administration, T3 and T4 levels were measured again after 2 and 4 hours respectively.
• To monitor pregnancy status, transrectal ultrasonography was performed beginning 16 days after ovulation.

Results

• Baseline T3 and T4 levels appeared to vary widely amongst the broodmares. However, following TRH administration, all mares except two, showed an increase in serum T3 and T4 concentrations.
• The overall pregnancy rate among the broodmares was found to be 76%. Upon comparing T3 and T4 levels in pregnant mares with those who didn’t get pregnant, no significant difference was observed.

Conclusions

The researchers concluded that decreased thyroid activity is not a common factor for infertility in broodmares. Furthermore, they noted that treatment with thyroid hormone as a means to enhance fertility doesn’t hold evidence from this study. The research thus draws into question this practice’s efficacy.