Cystic ovarian follicles and thyroid activity in the dairy cow.

Thyroid activity affects the functionality of the reproductive axis and thyroid dysfunction has been associated with ovarian hyperstimulation syndrome and polycystic ovarian syndrome, in human medicine. This study investigates serum17-<beta> estradiol, progesterone, thyrotropic and thyroid hormone levels, in cyclic dairy cows on heat (Group H) and in dairy cows with ovarian follicular cysts (Group FC). Both 17-<beta> estradiol and progesterone serum concentrations were statistically higher in cystic than in cyclic cows (estradiol: 8.51±1.91 vs 6.32±1pg/mL) (progesterone: 0.49±0.17 vs 0.13±0.03ng/mL), whereas TSH and fT4 serum concentrations were statistically lower in cows with cystic ovarian follicles (COF), compared to cyclic ones (TSH: 2.48±1.31 vs 3.56±1.03ng/mL) (fT4: 5.86±1.69 vs 8.63±1.08). fT3 serum levels were similar, in both cystic and cyclic subjects (2.94±0.65 vs 3.02±0.9, respectively). Based on these results it was decided to examine the function of the thyrothropic axis of dairy cows in a similar manner to that conducted on humans. If severe hypothyroidism should be found, a hormone replacement therapy could be attempted in cystic cows refractory to "ordinary" therapies.