OVULATION RATE AND EMBRYONIC SURVIVAL IN CHINESE MEISHAN AND WHITE CROSSBRED PIGS

Two component traits of litter size of pigs, ovulation rate and embryonic survival, were examined in Meishan and composite white crossbred gilts and sows. At puberty, an ovulation rate of 12.5 was similar for Meishan (118 +/- 3 d of age) and crossbred gilts (217 +/- 3 d of age). The number of corpora lutea (CL) increased (4.3 CL) markedly (P < .01) from puberty to the sixth estrous period (220 d of age) in Meishan gilts but increased (1.2 CL) slightly from puberty to the fourth estrous period in crossbred gilts. At 220 and 280 d of age, Meishan gilts had a greater (P < .01) number of CL than did crossbred gilts (220 d, 16.7 +/- .5 vs 12.7 +/- .4; 280 d, 16.5 +/- .7 vs 13.9 +/- .6 C L). Ovulation rate was greater ( P < .01) in Meishan than in crossbred sows examined at 417 (18.1 +/- 1.2 vs 15.2 +/- .4 CL), 608 (20.1 +/- 1.3 vs 17.1 +/-.6 CL), and 735 d of age (24.6 +/- .8 vs 16.6 +/- .8 CL). Early embryonic survival was not significantly different in this study for Meishan and crossbred gilts (73 vs 81%, respectively). However, at 30 d of gestation embryo weight and length, placental weight, and allantoic fluid volume were less (P < .01) in Meishan than in crossbred gilts. The effect of small embryo size and reduced placenta weights and allantoic fluid volumes at d 30 of gestation on subsequent fetal survival and development (uterine capacity) is unknown but may be an enhancement to the prolificacy of Meishan pigs. This observation indicates the need for further study of fetal-maternal interactions after d 30 of gestation in both Meishan and European pigs because of potential breed differences in uterine and placental function.