Effect of litter size and parity on the reproductive performance of hyperprolific sows with a focus on mummified fetuses

Background The objective of this study was to evaluate the effects of litter size and parity on the overall reproductive performance of highly prolific sows, with special emphasis on factors influencing the incidence of mummified fetuses and prenatal mortality. Data from 950 litters produced by 444 highly prolific DanBred sows were analyzed. The independent effects of parity and litter size on the total number of piglets born, born alive, stillborn, and mummified fetuses were evaluated. A linear mixed-effects model (LMM) with sow as a random intercept was applied to account for the repeated-measures data structure; group differences were evaluated using Wald χ² tests. Results Litter size significantly affected all evaluated reproductive traits ( P < 0.0001). Hyperprolific litters achieved the highest number of live-born piglets but also exhibited a significant increase in both stillborn and mummified fetuses ( P < 0.0001). Parity significantly influenced the number of total born, born alive, and stillborn piglets ( P < 0.01), with a severe increase in stillbirths observed in older sows at parity 7 and 8. Notably, parity had no statistically significant effect on the incidence of mummified fetuses ( P = 0.127), suggesting that mummification is primarily associated with larger litter sizes and limited uterine capacity rather than maternal age per se. Conclusions To optimize production and reduce perinatal losses, targeted management of sows beyond the fifth parity should be considered, as advancing parity significantly increased stillbirth rates. Fetal mummification is predominantly driven by intrauterine crowding in large litters rather than by maternal age.