Influence of hypo- or hyperthyroidism on ovarian function in Brahman cows

Area of Science:

• Reproductive Endocrinology
• Animal Science
• Veterinary Medicine

Background:

• Thyroid hormones play a crucial role in metabolic regulation and reproductive function in cattle.
• Understanding the impact of altered thyroid status on ovarian cycles is essential for livestock management.

Purpose of the Study:

• To investigate the effects of induced hyperthyroidism and hypothyroidism on ovarian function and reproductive parameters in multiparous Brahman cows.
• To assess the influence of altered thyroid status on estrous cycle length, follicular dynamics, and hormonal profiles.

Main Methods:

• Twenty-one Brahman cows were assigned to three groups: control (corn oil), hyperthyroid (triiodothyronine - T3), and hypothyroid (6-n-propyl-2-thiouracil - PTU).
• Thyroid status was altered for three estrous cycles, with blood sampling for hormone analysis (T3, T4, P4, TSH, cortisol, insulin, GH).
• Body weight (BW), body condition score (BCS), and estrous cycle parameters were monitored.

Main Results:

• Induced hyperthyroidism and hypothyroidism significantly altered thyroid hormone levels and affected BW and BCS.
• Hyperthyroid cows showed a higher incidence of abnormal estrous cycle length, with some becoming anestrous.
• For cows maintaining normal cycles, induced thyroid status did not alter follicular wave dynamics, dominant follicle size, ovulatory follicle size, or progesterone profiles.

Conclusions:

• Induced hyper- or hypothyroid status in Brahman cows did not negatively impact ovarian function in those that maintained normal estrous cycles.
• Altered thyroid status can disrupt estrous cycle regularity and influence body condition, highlighting the importance of thyroid hormone balance in reproduction.