Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: October 26, 2004
Publication Date: September 1, 2005
Citation: Freking, B.A., Leymaster, K.A., Christenson, R., Vallet, J.L. 2005. Prenatal mortality throughout gestation in lines of pigs selected for either ovulation rate or uterine capacity [abstract]. Midwestern Section of the American Society of Animal Science. 83(Suppl. 2):41. Paper No. 28. Technical Abstract: Selection for 11 generations for either ovulation rate (OR) or uterine capacity (UC) resulted in 19.6% greater prenatal survival at term in UC compared to OR. Our objective was to characterize prenatal mortality throughout gestation in each line, including the unselected control line (CO). A sample of 50 gilts from each line for each of three farrowing seasons was subjected to unilateral-hysterectomy-ovariectomy surgery at approximately 160 d of age and mated within line at approximately 280-d age. Gilts were assigned within sire to be harvested at d 25, 45, 65, 85, or 105 of gestation. Ovulation rate and number of live fetuses were recorded for each pregnant gilt (n = 298). A mixed model analysis of variance was conducted. Fixed effects of farrowing group, line, gestation age, and two-way interactions were fitted. The random effect of sire (n = 88) of the gilt within farrowing group and line was used to test line differences. Ovulation rate of OR line gilts (18.3 ± 0.3) exceeded (P < 0.001) both the CO and UC line, 15.3 ± 0.3 and 14.1 ± 0.3, respectively. Line by gestation age interacted to affect number of live fetuses (P < 0.001). Least squares means for CO line were 10.7, 8.3, 7.9, 7.0, and 7.2 live fetuses for d 25, d 45, d 65, d 85, and d 105, respectively (average SE = 0.52). Corresponding means from the OR line were 13.6, 8.5, 8.1, 6.4, and 6.5 live fetuses, respectively (average SE = 0.49). UC line means were 10.3, 9.3, 8.4, 7.8, and 7.9 live fetuses, respectively (average SE = 0.53). In each line the number of live fetuses at d 25 was about 72% of ovulation rate. Mortality was highest in the OR line, intermediate in the CO, and lowest in the UC line to d 45. Losses continued to occur from d 45 to d 105 but line differences in number of fetuses at d 45 were maintained to d 105. Selection for uterine capacity has improved fetal survival during the critical time period between d 25 and d 45.