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 follicle growth and regression by ultrasound imaging in vivo. Ultrasound scanning was performed daily. Follicles were obtained at ovariectomy; follicular fluid was collected for assay, and the degree of atresia was assessed histologically. Histological atresia was correlated with growth patterns when anovulatory growing and regressing follicles were compared (P < 0.05), but was not different between growing and static follicles. Oestradiol concentrations were lower in static than in growing follicles, although the difference was not significant (35 +/- 7 versus 260 +/- 120 ng ml-1; P < 0.08), and were significantly lower in regressing follicles (7 +/- 5 ng ml-1; P < 0.05). Oestradiol concentrations were significantly lower in histologically atretic than in nonatretic 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 oestradiol concentration and the number of days the follicle was visible by ultrasound (r = -0.71; P < 0.001). Concentrations of progesterone in follicular fluid were correlated with the number of days the follicles were 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) but not significantly higher in atretic compared with nonatretic follicles (129 +/- 102 versus 53 +/- 15 ng ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)