Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: 4/4/2002
Publication Date: 9/1/2002
Citation: CHRISTENSON, R.K., LEYMASTER, K.A. CORRELATED RESPONSES IN GRAVID UTERINE, FARROWING AND WEANING TRAITS TO SELECTION OF PIGS FOR OVULATION RATE OR UTERINE CAPACITY. PROCEEDINGS OF 7TH WORLD CONGRESS OF GENETICS APPLIED TO LIVESTOCK PRODUCTION. 2002. SESSION 08, REPRODUCTION. CD-ROM COMMUNICATION NO. 08-25. Interpretive Summary:
Technical Abstract: One hundred six gilts of each line were randomly assigned to either UHO or intact groups in each of two seasons (March and September) of 1999 and 2000. Gilts were UHO at 160 days of age, mated within line, and slaughtered at 105 days of gestation. At slaughter, the remaining gravid uterine horn and ovary were recovered and weighed. The broad ligament was trimmed from the uterine horn. The ovary was dissected and number of CL recorded. Each fetus was exteriorized, and classified as alive or dead. A blood sample was taken from each live fetus and fetal sex and weight were recorded. The placenta from each fetus was removed from the uterine horn and weighed. Intact gilts were mated within line, laparoscoped at 40 days of gestation to determine number of CL, and were allowed to farrow. At farrowing, normal husbandry procedures were used and pigs were weaned at 18 days. Under crowded uterine conditions, increased ovulation rate of OR gilts did not increase uterine capacity (number of live fetuses) at 105 days of gestation (OR vs CO; 6.3 vs 6.8 fetuses), but prenatal mortality (n = ovulation rate minus live pigs) was increased (P < 0.01) in OR gilts as compared to CO gilts (n = 10.8 vs 7.5). However in UC gilts, uterine capacity (number of live fetuses) was increased (P < 0.01) at 105 days of gestation (UC vs CO; 7.9 vs 6.8 fetuses) and prenatal mortality was lower (P < 0.01) in UC than in CO gilts (n = 6.1 vs 7.5). Part of this enhanced fetal survival is evident in the lower (P < 0.05) number of mummies observed at 105 days of gestation in UC versus CO versus OR gilts (0.8 vs 1.3 vs 1.6 mummies, respectively). Gravid uterine horn weight was greater (P < 0.01) in UC, intermediate in CO and lower in OR gilts. This result is primarily influenced by number of fetuses and associated tissues of pregnancy and secondarily influenced by empty uterine horn weight for CO, OR and UC gilts (1.8 +/ 0.03, 1.9 +/ 0.03, and 2.0 +/ 0.04 kg, respectively). Average fetal weight tended to be less for OR than for the CO and UC gilts. This result may be a reflection of the more severe crowding experienced by OR embryos and(or) fetuses as suggested by lighter placental weights in the OR than in CO and UC gilts. That crowding was more severe in OR gilts is supported by the previously discussed increase in prenatal mortality in the OR gilts. Average fetal and placental weights did not differ for CO and UC gilts, despite UC averaging 1.1 more fetuses at 105 days of gestation. Total litter fetal and placental weights were greater (P < 0.01) in UC gilts, due to increased number of live fetuses, intermediate in CO, and lower in OR gilts. In intact gilts, increased ovulation rate or uterine capacity resulted in a nonsignificant improvement of total number of pigs or live pigs at birth. Number of mummies and prenatal mortality were greater in OR than CO or UC gilts, supporting previous observations that increasing ovulation rate by direct selection or superovulation has minimal effects on litter size at farrowing. In addition, because ovulation rate was insufficient in UC gilts, litter size in the UC line did not increase significantly. Thus, simultaneous selection emphasis to increase both ovulation rate and uterine capacity are necessary to increase litter size.