54 Evaluation of uterine capacity during late gestation in young commercial females over the past twenty years

Over the past two decades, litter size has increased substantially in commercial swine production. However, there has been a consequential increase in preweaning piglet mortality due to reductions in piglet birthweight and greater within-litter variation. Uterine capacity (UC) plays a significant role in litter size and corresponding birthweights. Therefore, the objective of this study was to evaluate changes in UC during late gestation in young commercial females from different commercial genetics over the past 20 years. Three composite populations generated at the USMARC were evaluated for this study (lines 123, 124, and 125). Line 123 consisted of F1 Yorkshire and Landrace genetics with a single sampling in 2001 from multiple commercial maternal line sires of lean Landrace and high marbling Duroc. This line was maintained by inter se mating for 10 years. In 2011, Line 124 and Line 125 were established utilising F1 Line 123 sows and continuous sampling from multiple commercial maternal line sires (Line 124, Landrace; Line 125, Yorkshire) in alternating years. For evaluation of UC, gilts were bred using standard protocols and harvested at Day ~110 of gestation. Ovulation rate (OR), total fetuses, viable fetuses (UC), fetal mortality, fetal and placental weights, placental efficiency (fetal/placental weight ratio), and variation in fetal and placental weights (based on coefficient of variation) were measured postmortem. Gilts from Line 123 (n = 10) were sampled in 2010; whereas gilts from lines 124 (n = 56) and 125 (n = 28) were sampled between 2019 and 2023. All data were analysed using PROC GLM with the fixed effect of line and gestation age as a covariate. There were increases (P < 0.05) observed in OR, total fetuses, and UC from both newer genetic lines 124 and 125 compared to the older Line 123. Fetal survival, based on number of viable fetuses and OR, were not different (P > 0.10) between the lines. However, late fetal mortality as assessed by number of observable mummies tended (P = 0.06) to be greater in Line 125 gilts compared to Line 123 with Line 124 intermediate between the lines. No differences (P > 0.10) in fetal weight or the variation in fetal weight were observed between the lines across selection. A tendency (P = 0.08) in placental weight and significance (P = 0.04) in placental weight variation was observed in which Line 124 gilts produced larger placentas with greater variation compared to Line 123 and Line 125 was intermediate. As a result, Line 124 gilts had reduced (P = 0.05) placental efficiency compared to Line 123 gilts. These data illustrate that increased selection of litter size over the past two decades are reflective of increased OR and UC. In young females, fetal weight and variation differences are not apparent; however, differences in placental development are apparent as genetic selection for litter size has increased. Therefore, using approaches to target improved placental development and function provide a mechanism to improve piglet litter quality and weaning survivability.

USDA is an equal opportunity provider and employer.