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Quantitative Variation in Ovarian and Follicular Development in Four Genetic Groups of Pigs at Different Ages¹

University of Wisconsin, Madison

Abstract

Variations in the development of the ovary and differences in the number of follicles at different ages were studied in gilts of the Yorkshire (YY) and Poland China (PP) breeds and in their reciprocal crosses. A total of 86 gilts was killed at day of birth, and at 42 and 70 days of age. Estimates were made of the weight of the ovary, the numbers of primary follicles at day 0 and day 42, secondary follicles at day 42 and the tertiary follicles at day 70.

Weight of the ovaries at the day of birth was higher in the crossbred gilts than in the purebred gilts. The difference in the weights of immature ovaries was not associated with the number of primary follicles. The correlation coefficient between body weight and ovarian weight within the genetic groups at the day of birth was not significant.

Weight of the ovaries of the PP gilts at the day of birth was slightly higher than those of the YY gilts but at day 42 the ovaries of the YY gilts weighed significantly more than those of the PP gilts, suggesting that the postnatal development of the ovary is faster in the YY gilts than in the PP gilts. The number of secondary follicles was significantly larger in the YY gilts than in the PP gilts at day 42. The decline in number of follicles between the day of birth and day 42 (indication of follicular atresia) was greater in the PP than in YY gilts (P=.11).

The left ovary was found to be heavier than the right at day 42. The potential for this difference was not grossly visible at the time of birth but differentiated by the later stage.

¹ This work was done under a cooperative agreement between the Research Division of the College of Agricultural and Life Sciences, University of Wisconsin, and the Animal Husbandry Research Division, A.R.S., U.S.D.A., and supported in part by Cooperative U.S.D.A.-C.S.R.S. Grant No. 816-15-20. It was also supported in part by the Ford Foundation, Grant No. 63–505. Published with the approval of the Research Division of the College, Paper No. 1284 from the Laboratory of Genetics and No. 547 from the Department of Meat and Animal Science.