Reproductive patterns in cyclic and pregnant thyroidectomized mares.

The research studied the reproductive patterns and behavior in mares that had their thyroid surgically removed compared with healthy, intact mares. The research found that while there were some physical and behavioral changes in the thyroidectomized mares, it had little impact on their fertility and oestrous cycles, and they were still able to achieve pregnancy.

Introduction and Methodology

• The research article focuses on the study of reproductive patterns in mares that had undergone thyroidectomy, which is the surgical removal of the thyroid gland.
• Three Quarter-horse mares were thyroidectomized at approximately 1.5 years of age, and three similar intact mares served as the control group.
• The study was conducted over two breeding seasons.

Observations and Results

• The thyroidectomized mares displayed some altered physical characteristics such as lethargy, oedematous (swollen due to fluid accumulation) rear limbs, and coarse hair coats.
• The behavior during oestrus (the period of sexual receptivity in female animals) changed, becoming more tranquil when exposed to a stallion, and they were mildly antagonistic when not in this phase.
• The length of the oestrous cycles among the thyroidectomized mares varied, but most often were between 19-24 days long.
• The duration of oestrus for the control and thyroidectomized mares was not significantly different (P greater than 0.05), indicating that the thyroidectomy did not have a significant impact on the duration.

Hormone Levels and Pregnancy

• Despite the thyroidectomy, the level of luteinizing hormone (LH) during oestrus and peak progestagen after ovulation did not significantly differ between the two groups of mares (P greater than 0.05).
• Pregnancy was achievable in both groups of mares, implying that the thyroid gland isn’t critical for a mare’s ability to conceive and maintain a pregnancy.
• In one case, Thyroxine (a hormone produced by the thyroid gland) was detectable in one pregnant thyroidectomized mare during the last two-thirds of pregnancy only.