| Abstract: | The effect of chronic administration of adrenocorticotropin on ovarian follicular development was studied. Twelve nonlactating Holstein cows received either 100 IU adrenocorticotropin (n = 6) or saline (n = 6) at 12-h intervals, commencing d 16 and continuing until d 23 of an induced estrous cycle (estrus = d 0). Cows were slaughtered on d 24, ovaries collected, and number of visible antral follicles recorded. Estradiol-17 beta, androstenedione, and testosterone in follicular fluid, and luteinizing hormone and follicle-stimulating hormone receptors in follicular tissue of the largest follicles were determined. Largest follicles were classified as ovulatory or nonovulatory based on the estrogen to androgen ratio. One cow treated with adrenocorticotropin, but none treated with saline, had ovulated by slaughter. The numbers of small, medium, and large antral follicles were 0, 1, and 5 for cows treated with adrenocorticotropin and 0, 1, and 6 for cows treated with saline. Follicular diameter (15.0 +/- 1.0 versus 14.0 +/- 2.0 mm) and follicular fluid volume (2.9 +/- .8 versus 2.2 +/- .5 ml) of the largest follicle in cows treated with adrenocorticotropin or saline were not different. No differences were found in the number of luteinizing hormone and follicle stimulating hormone receptors nor in the proportion of ovulatory versus nonovulatory follicles between treatments. We conclude that adrenocorticotropin administered at 100 IU every 12 h during the follicular phase does not significantly alter follicular development in the nonlactating dairy cow. |
