This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Price, C. A. Articles by Groome, N. P. Search for Related Content PubMed Articles by Price, C. A. Articles by Groome, N. P.

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). The progesterone:oestradiol ratio was significantly correlated with the number of days a follicle was detected by ultrasound (r = 0.8; P < 0.001) and was significantly higher in regressing than in growing follicles, and higher in atretic than in nonatretic follicles (P < 0.05). Concentrations of dimeric inhibin in follicular fluid were not significantly correlated with number of days that a follicle was detected by ultrasound (P > 0.05), but were significantly (P < 0.05) higher in regressing (3.0 ± 0.7 µg ml^–1) than in growing or static follicles (1.2 ± 0.2 versus 1.1 ± 0.2 µg ml^–1). Inhibin concentrations were not significantly affected 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 µg 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 follicles (P > 0.05). These results demonstrate that growing follicles contain high oestradiol and low progesterone and dimeric inhibin concentrations and that, as the rate of growth of the follicle slows, oestradiol concentrations decrease, but progesterone and dimeric inhibin concentrations do not increase until the follicle starts to regress. Histological indices of atresia did not closely correlate with either morphological or endocrinological measures of follicular growth.