Hormonal Profile of Ovarian Follicular Fluid and Blood Plasma during Different Stages of Estrous Cycle in Holstein Cattle

The aim of this study was to evaluate the concentrations of reproductive hormones in blood plasma and in follicular fluids of different sized follicles during various stages of the estrous cycle in Holstein cattle. Jugular blood samples from 42 adult Holstein cattle were collected immediately after the slaughter. Antral fluids from small (4-5 mm), medium (6-9 mm) and large (10-20 mm) follicles were collected and the stages of estrous cycle were recorded. The gonadotropin and steroid concentrations in blood plasma and steroid levels in follicular fluid were measured. Estradiol-17-ss concentrations in antral fluids of small follicles in early diestrous were significantly (P<0.05) higher than the concentration of that in the follicular fluids from small antral follicles in other stages of the estrous cycle. Concentrations of estradiol-17-ss in follicular fluids from medium antral follicles in metestrous were significantly (P<0.05) higher than that of those in pro-estrous and estrous phase of the estrous cycle. There were no significant differences in the follicular fluid concentrations of estradiol-17-ss from the large follicles among the various stages of estrous cycle (P>0.05). The variation in progesterone concentration within the follicles of various size during different phases of estrous cycle was not significant (P>0.05). The plasma concentrations of FSH, LH and estradiol-17-ss in proestrous and estrous were higher than the other stages of the cycle (P<0.05). The plasma progesterone concentration in late diestrous was higher than in metestrous, proestrous and during estrous (P<0.05).