Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 26, 2001
Publication Date: May 20, 2001
Citation: Wise, T.H., Christenson, R.K., Leymaster, K.A., Ford, J.J. 2001. Fetal and neonatal ovarian weights and oocyte numbers in lines that differ for ovulation rate [abstract]. Proceedings Sixth International Conference on Pig Reproduction, Columbia, Missouri, p. 28. (Abstract No. 4) Technical Abstract: Swine breeds or genetic lines selected for enhanced ovulation rate have not been shown to have major differences in endocrine profiles. It was hypothesized that differences in ovulation rate may be the result of greater numbers of oocytes that could be recruited into the growing pool of follicles destined to ovulate. There are two critical periods in which oocyte numbers could be altered in utero which may result in increased numbers of oocytes in the adult during the mitogenic increase in germ cells after migration to the germinal ridge and a mitogenic increase prior to birth when the maximum number of oocytes are found in the ovary as egg cell nests. White composite gilts selected for increased ovulation rate (OR) have an ovulation rate of 17.1 +/ .2, n=439, vs 14.2 +/ .2, n=481, for the control line. Fetal ovarian weights (n=931) were collected at 105 d of gestation from the control and OR line, an approximate time when oocyte numbers should be maximal. Right ovarian weight was greater in the OR line than the control line (38.2 +/ .7 vs 32.2 +/ .7 mg, respectively; p<.01), but more importantly, the frequency of heavy ovaries was greater in the OR line. After collagenease digestion (one right ovary per litter), oocyte numbers were greater in the ovaries from the OR line as compared to ovaries of the control gilts (144.4 x 10**4, n=78, vs 90.7 x 10**4, n=73, respectively; p<.01). The aspect that the ovary is a constantly evolving tissue (development and regression of follicles/oocytes) probably makes ovarian weight of limited value in predicting subsequent ovulation rate. Either increased oocyte numbers in egg cell nests or reduced apoptosis shortly after birth still may be a supportable mechanism linked to increased ovulation rate.