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Characterization of Antral Follicle Populations during the Estrous Cycle in Pigs Selected for Ovulation Rate¹

University of Nebraska, Lincoln 68583-0908

Abstract

The objectives of this study were to characterize and compare ovarian follicular populations in Gene Pool Control (GPC, randomly selected) and Relax Select line (RS, nine generations of selection for high ovulation rate followed by six generations of random selection) gilts during different stages of the estrous cycle. Thirty-five RS and 23 GPC gilts were allotted randomly within litter for ovary recovery on either d 3, 15 or 19 of the estrous cycle. Surface follicles on the ovaries were classified by size (small, < 3 mm; medium, 3 to 6.9 mm; large, 7 to 12 mm), and counts were recorded for each ovary. Ovarian weight (OW), number of corpora lutea (CD, follicular fluid volume (FFV) from small, medium and large follicles, residual ovarian weight and follicular fluid weight (FFW) also were recorded. Total numbers of small and medium follicles were greatest on d 15, whereas total number of large follicles and FFW were greatest on d 19. The OW, FFW and follicle numbers of all classes were lowest on d 3. The RS gilts expressed longer interestrous intervals (21.9 vs 20.4 d, P < .05) and higher ovulation rates (18.5 vs 15.3 CL, P < .01) than GPC gilts. The left ovary of RS gilts was responsible for most of the ovulation rate advantage (10.3 vs 7.4 CL, P < .01) Overall, GPC gilts had more total small follicles than RS gilts (P < .01). The advantage was due primarily to higher numbers of small follicles at d 15. This difference contributed to the day x line interaction for FFV from small follicles; GPC gilts had greater FFV in small follicles than RS gilts on d 15, but the reverse was true on d 19- Follicular population differences on days of the estrous cycle evaluated in the present study failed to provide a basis for the difference in ovulation rate brought about by genetic selection for high ovulation rate.

¹ Published as Paper No. 8280, Journal Series, Nebraska Agric. Res. Div.

² Present address: The Upjohn Company, Kalamazoo, MI 49001.

³ To whom reprint request should be addressed. Dept. of Animal Sci., University of Nebraska, Lincoln 68583-0908.