COMPARISON OF HORMONAL AND HISTOLOGICAL-CHANGES DURING FOLLICULAR-GROWTH, AS MEASURED BY ULTRASONOGRAPHY, IN CATTLE

The aim of the study was to compare histological and endocrinological indices of ovarian follicle health in cattle with monitoring of follic le growth and regression by ultrasound imaging in vivo. Ultrasound sca nning was performed daily. Follicles were obtained at ovariectomy; fol licular fluid was collected for assay, and the degree of atresia was a ssessed histologically. Histological atresia was correlated with growt h patterns when anovulatory growing and regressing follicles were comp ared (P < 0.05), but was not different between growing and static foll icles. Oestradiol concentrations were lower in static than in growing follicles, although the difference was not significant (35 +/- 7 versu s 260 +/- 120 ng ml(-1); P < 0.08), and were significantly lower in re gressing follicles (7 +/- 5 ng ml(-1); P < 0.05). Oestradiol concentra tions were significantly lower in histologically atretic than in nonat retic follicles (16 +/- 8 versus 282 +/- 132 ng ml(-1); P < 0.05), but were not different between nonatretic and early atretic follicles (P > 0.05). There was a significant negative correlation between oestradi ol concentration and the number of days the follicle was visible by ul trasound (r = -0.71; P < 0.001). Concentrations of progesterone in fol licular fluid were correlated with the number of days the follicles we re detected (r = 0.61; P < 0.01) and were higher in regressing than in growing follicles (122 +/- 71 versus 48 +/- 13 ng ml(-1); P < 0.05) b ut not significantly higher in atretic compared with nonatretic follic les (129 +/- 102 versus 53 +/- 15 ng ml(-1)). The progesterone:oestrad iol ratio was significantly correlated with the number of days a folli cle was detected by ultrasound (r = 0.8; P < 0.001) and was significan tly higher in regressing than in growing follicles, and higher in atre tic than in nonatretic follicles (P < 0.05). Concentrations of dimeric inhibin in follicular fluid were not significantly correlated with nu mber of days that a follicle was detected by ultrasound (P > 0.05), bu t were significantly (P < 0.05) higher in regressing (3.0 +/- 0.7 mu g ml(-1)) than in growing or static follicles (1.2 +/- 0.2 versus 1.1 /- 0.2 mu g ml(-1)). Inhibin concentrations were not significantly aff ected by degree of atresia. Oestradiol concentrations of preovulatory follicles were significantly higher than those of regressing follicles (1131 +/- 382 versus 35 +/- 7 ng ml(-1); P < 0.05) and concentrations of dimeric inhibin were lower (1.0 +/- 0.2 versus 3.9 +/- 0.4 mu g ml (-1); P < 0.05). Oestradiol and inhibin concentrations were negatively correlated (r = -0.65; P < 0.05). Dimeric inhibin concentrations were similar between growing nonovulatory and presumptive preovulatory fol licles (P > 0.05). These results demonstrate that growing follicles co ntain high oestradiol and low progesterone and dimeric inhibin concent rations and that, as the rate of growth of the follicle slows, oestrad iol concentrations decrease, but progesterone and dimeric inhibin conc entrations do not increase until the follicle starts to regress. Histo logical indices of atresia did not closely correlate with either morph ological or endocrinological measures of follicular growth.