Ovarian Response to Injections of Charcoal-Extracted Porcine Follicular Fluid and Porcine Follicle-Stimulating Hormone in Gilts Fed a Progesterone Agonist (Altrenogest)1

This experiment was conducted to compare the negative effects of charcoal-extracted porcine follicular fluid (pFF) and the positive effects of purified porcine follicle-stimulating hormone (pFSH) on growth of follicles and on plasma hormone concentrations. Twenty gilts were fed altrenogest for 18 days (20 mg.day−1.gilt−1) to suppress spontaneous growth of large follicles (> 6 mm in diameter). Gilts, assigned at random to receive pFF and pFSH administered in a 2 × 2 factorial arrangement, were injected 9 times at 8-h intervals starting 48 h before the last feeding of altrenogest and ending 8 h before slaughter (24 h after the last feeding of altrenogest). Blood was collected periodically through vena cava catheters. Treatment groups and mean number of medium follicles (3 to 6 mm in diameter)/gilt at necropsy were 1) 20 ml of charcoal-extracted porcine serum i.v. + 4 ml saline i.m., 30.8; 2) 20 ml of pFF i.v. + saline i.m., 0.2; 3) serum i.v. + 8 μg of pFSH (USDA-pFSH-B1)/kg BW in saline i.m., 59.0; and 4) pFF i.v. + pFSH in saline i.m., 36.2. Injections of pFF decreased (p < 0.01) and injections of pFSH increased the number of medium follicles, and the interaction of pFF and pFSH was not significant. Plasma FSH decreased (p < 0.01) during pFF treatment of saline-injected gilts at a rate of 0.29 ng.ml−1.h−1. During pFSH treatment, plasma FSH increased (p < 0.05) at statistically identical rates of 0.33 and 0.32 ng.ml−1.h−1 in serum- and pFF-injected gilts. Medium follicles were fewer in gifts injected with pFF-pFSH than in gilts with serum pFSH, even though their plasma FSH profiles were identical Plasma concentrations of luteinizing hormone, estrogen and progesterone and numbers of small (1 to 2 mm in diameter) and large follicles, did not differ significantly between treatments. Results in altrenogest-fed gilts indicate that 1) pFSH recruited additional medium follicles, but did not cause growth of preovulatory follicles, and 2) growth of medium follicles may be regulated in part by factors produced in the ovary that antagonize the action of FSH at the ovarian level.