Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2002
Publication Date: 5/15/2003
Citation: MCCOARD, S.A., WISE, T.H., FORD, J.J. 2003. GERM CELL DEVELOPMENT IN MEISHAN AND WHITE COMPOSITE GILTS. ANIMAL REPRODUCTION SCIENCES. v. 77(1-2). p. 85-105. Interpretive Summary: Chinese Meishan pigs are genetically diverse compared to breeds of pigs used in U.S. swine production. This breed was imported into the U.S. for scientists to investigate the biological basis for greater number of piglets that Meishan females produce compared to similar aged females of U.S. breeds. In the present study, ovarian development was investigated during late pregnancy and early postnatal life to determine what factors, if any, may explain the higher number of ovulations that characterize Meishan females. Ovaries were obtained from Meishan and Yorkshire x Landrace crossbred fetuses at 60, 75, 90 and 105 days of gestation and on postnatal ages of 1, 7, 14, 25 and 56 days. Ovarian development was surprisingly similar in females of these two breeds during the last one-half of gestation and the first 14 days of life. Thereafter at 25 and 56 days of age, ovaries from Meishan females had greater follicular development supportive of the earlier age at puberty in this breed. These findings will guide scientists in the design of subsequent studies related to improvement of litter size in swine.
Technical Abstract: This study compared dynamics of the germ cell population in two swine breeds that differ in prolifacy, White Composite (WC) and Meishan (MS), during fetal and neonatal life and in mature sows. Germ cell populations developed in a similar pattern in these two diverse breeds during fetal life. Maximal germ cell number was observed at 90 days postcoitum (dpc) in both WC and MS gilts, and substantial oogonial apoptosis was evident thereafter with approximately 30% of maximal numbers present at 25 days postpartum (dpp). Neither gilt nor sow germ cell number was correlated with maternal ovulation rate. Postnatal MS gilts had larger pools of primordial follicles and consistently greater proportions and numbers of primary and secondary follicles compared to postnatal WC gilts, indicative of enhanced follicular recruitment and primordial follicle activation. Occasional antral follicles were present in MS ovaries by 25 dpp and numerous surface follicles were observed at 56 dpp in MS but not WC ovaries, indicative of more rapid ovarian maturation and early onset of puberty. Total germ cell number is unlikely to influence or to predict subsequent ovulation rate. These observations highlight important developmental events during late fetal and early postnatal life that prepare the ovarian environment for early onset of puberty and subsequent ovulation in MS gilts.