PS9-25. Effects of Skipped Mating at the First Post-weaning Estrus on Reproductive Outcomes of First Parity Sows and Lifetime Offspring Performance.

Abstract Reducing nonproductive days has been a priority in commercial sow management to maximize performance. However, first-parity sows face growth and lactation demands that can impair later reproductive performance. Skipping mating at the first post-weaning estrus is a management strategy that can improve reproductive performance of first-parity sows. The objective of this study was to evaluate effects of this strategy on farrowing performance and growth of offspring. This study was conducted on a commercial sow farm in southwestern Minnesota that recently re-populated. First parity sows (Acufast 276) were mated to DNA 600 sires and were categorized according to management strategy as either mated at the first post-weaning estrus (Control; n = 283) or mated at the second post-weaning estrus (heat-not-served; HNS; n = 419). Farm policy was to skip mating first-parity sows at first estrus; however, some sows were mated at first postweaning estrus to meet breeding targets. Data were extracted from a controlled trial that evaluated timing of zinc supplementation during gestation. No Zn × management strategy interactions were detected so data were pooled across Zn treatments. Gestation and lactation performance and offspring weights were recorded by researchers, whereas sow gestation feed intake and reproductive performance in the subsequent cycle were obtained from commercial farm records. Piglet outcomes were evaluated from birth to weaning (n = 8,837), and a subset of pigs was followed to market weight (n = 859). Management strategy (Control vs HNS) was included in the statistical model as a fixed effect. For sow-level outcomes, continuous variables were analyzed using linear models with Type III ANOVA and binary outcomes using logistic regression. For piglet-level outcomes, linear mixed models were used for continuous variables and generalized linear mixed models with a binomial distribution for binary variables, with sow included as a random effect. HNS sows consumed less feed during gestation than control sows, excluding the 21-d period before breeding (Table 1). HNS sows farrowed more total piglets and piglets born alive per litter than Control sows. However, HNS sows also farrowed more stillborn piglets and mummified fetuses than Control sows. Despite the larger litter size at birth, the number of piglets weaned did not differ between treatments (P ≥ 0.15), likely due to cross-fostering practices. HNS sows had greater body condition at breeding but lower body condition at weaning (P ≤ 0.048). Offspring from HNS sows were lighter at birth and weaning, with a tendency toward lower market weight than offspring from Control sows. In the subsequent reproductive cycle, when all sows were mated at the first post-weaning estrus, sows previously managed as HNS produced larger litters than Control sows. Skipped mating at the first post-weaning estrus in first-parity sows improved reproductive performance across two cycles, but slightly decreased growth performance of offspring. For image description, please refer to the figure legend and surrounding text.