Effect of administration of porcine follicular fluid to gilts during the luteal phase of the estrous cycle on plasma gonadotropins, follicular development, and ovulation rate

Eighty gilts were assigned randomly to receive twice daily i.v. injections of either 5 mL of steroid-reduced porcine follicular fluid (pFF) or .15 M saline (S) to evaluate the effects of suppression of FSH before, during, and 1 d after induced luteolysis on d 13 (d 0 = onset of estrus) on development of medium and large follicles during the follicular phase and subsequent ovulation rate. Ovaries were recovered and assessed for numbers of corpora albicantia (CA) and medium (NMF, 3 to 6.9 mm) and large (NLF, > 6.9 mm) follicles on d 13, 15, and 17 of the estrous cycle and number of corpora lutea (CL) in the group assigned to be examined after ovulation. Gilts assigned to the postovulatory group were bled at 12-h intervals from d 9.5 through 17. Administration of pFF suppressed concentrations of FSH during treatment with pFF (pFF, .38 +/- .02 vs S, .52 +/- .02 ng/mL, P < .05) and reduced NMF on d 13 (pFF, 17.3 +/- 4.0 vs S, 45.8 +/- 4.0, P < .01) and d 15 (28.1 +/- 4.0 vs 38.7 +/- 4.2, P < .05). The NMF declined markedly between d 15 and 17 in control gilts but not in pFF-treated gilts; pFF and S gilts had achieved similar NMF on d 17 (pFF, 23.1 +/- 4.0 vs S, 21.3 +/- 4.2). Large follicles were first observed on d 17 and were reduced substantially by prior treatment with pFF (pFF, 6.7 1.4 vs S, 12.4 +/- 1.5, P < .05). Ovulation rate and interval from prostaglandin F(2 alpha) to estrus were not affected by treatment with pFF from d 10.5 to 14. Follicle-stimulating hormone did not show a major elevation above pretreatment levels after withdrawal of pFF treatment on d 14; however, the pattern of FSH release between d 14.5 and 17 tended (P < .1) to differ between pFF- and S-treated gilts. The FSH levels are important for development and maintenance of the medium follicle population during the mid to late uteal and early follicular phases of the estrous cycle in pigs.