Follicle Stimulating Hormone and Estradiol-17β in Dairy Cows Treated with Progesterone-Releasing Intravaginal Devices

Abstract

Follicle stimulating hormone and estradiol-17β were measured by specific radioimmunoassay in samples of bovine plasma collected from five untreated cows and from five cows treated with progesterone-releasing intravaginal devices during the postpartum period. Mean follicle stimulating hormone concentration in plasma of untreated noncycling cows (n=2), untreated cycling (n=3), and treated cows (n=5) were 19.0ng/ml, 14.0ng/ml, and 22.6ng/ml. In cycling untreated cows and progesterone-treated cows, mean follicle stimulating hormone at estrus was elevated to 121.4ng/ml and 88.7ng/ml. Estradiol-17β averaged 4.3 pg/ml in both cycling and noncycling untreated cows and 5.5 pg/ml in progesterone-treated cows. In untreated cows estradiol was elevated 24h prior to estrus and peak follicle stimulating hormone concentration while in treated cows estradiol of plasma was highest, coinciding with estrus and peak follicle stimulating hormone at 36h after removal of the progesterone coil. Both hormones were variable between and within groups and were not different due to treatment. No significant relationship was detected between follicle stimulating hormone and estradiol in either cycling nontreated cows or progesterone-treated cows while the relationship between the two hormones was positive in noncycling untreated cows. Administration of progesterone-releasing devices during the estrous cycle may block peak follicle stimulating hormone in plasma until after removal and may alter estradiol profile of plasma prior to estrus.