Correlates of ovarian morphology, estrous behavior, and cyclicity in an inbred strain of miniature swine

Abstract

Ovarian morphology and behavioral relationships were studied in a group of nine miniature pigs with a characteristically small litter size (∼5) and an average coefficient of inbreeding of 0.39. The first day of standing estrus was designated as day 0. Laparoscopy was used to evaluate and photograph ovarian activity on days 1, 5, 11, 17, and day 2 of the subsequent estrous cycle. Mean (±SEM) duration of estrus and the estrous cycle was 3.1±0.2 and 22.6±0.3 days, respectively. An average of 9.0±0.4 vesicular follicles developed/estrous period and 96% of the follicles showed morphologic evidence of ovulation resulting in a mean of 8.6±0.3 corpora lutea (CL) per animal. There was no significant correlation between the degree of inbreeding and number of vesicular follicles (r=0.27) or CL (r=0.28) developing/cycle within the experimental group. Mature preovulatory follicle and CL size ranged from 6–12 mm and 8–12 mm in diameter, respectively, and 22.5% of the newly formed CL contained distinct postovulatory stigmata. These data indicated that 1) temporal relationships of sexual behavior and gross ovarian morphology in the miniature pig were similar to descriptions previously reported for the standard pig, and 2) the reduced litter size characteristic to this particular strain is, at least in part, due to decreased number of vesicular follicles developing during the estrous cycle.