Serum thyroxine concentrations and pregnancy rates 15 to 16 days after ovulation in broodmares.

The research evaluates if the concentration of thyroxine (T4) hormone in a mare’s blood is tied to pregnancy rates, and whether supplementing the thyroid hormone improves fertility. The study found no significant correlation, suggesting neither factors significantly affect the pregnancy outcome 15 to 16 days post ovulation.

Research Methodology

The researchers organised a cohort study design for this research, involving 329 clinically normal broodmares. These mares underwent examinations 15 to 16 days following ovulation to determine whether they were pregnant. Blood samples were taken simultaneously to measure serum T4 concentration.

• Mares in the study: Of these 329 mares, 60 had previously received thyroid hormone supplementation due to low serum T4 concentration (< 16 microg/dl) before breeding.

Data and Findings

The serum T4 concentration observed in these mares ran a range from 4.5 to 53.9 microg/dl, with distinct variations in results.

• 40 mares (12%) had low T4 concentration.
• 283 mares (86%) showed normal T4 concentration.
• 6 mares (2%) had high T4 concentration.
• 231 mares were found pregnant 15 to 16 days post ovulation.

Despite these variations in thyroxine levels, the researchers found no significant association between the serum T4 concentration (whether low, normal, or high) and pregnancy. This finding was confirmed using logistic regression analysis which showed serum T4 concentration was not significantly related to pregnancy.

Thyroid Supplementation and Pregnancy

Analysis of mares receiving thyroid hormone supplementation was similarly inconclusive.

• Among the 269 mares that didn’t receive thyroid hormone supplementation, 187 were pregnant.
• Out of the 60 mares that received the supplementation, 44 were being pregnant.

This led the researchers to conclude that there was no significant relationship between thyroid hormonal supplementation and pregnancy.

Conclusions

This research concluded that the serum T4 concentration in mares is not significantly associated with pregnancy 15 to 16 days after ovulation. Additionally, it implied that supplementing mares that have low T4 concentrations is not necessary, nor likely to bring about any beneficial effects. The absence of a significant relationship between thyroid hormone and pregnancy both in terms of natural concentration and in terms of supplementation has been clearly supported by the research data.