Peri-parturient sow posture patterns in relation to genetic merit for mothering ability and piglet crushing in crated and free-farrowing pens

Although genetic selection for mothering ability has improved piglet survival, the behavioral traits underlying this effect remain poorly understood. This study investigated how posture patterns vary between sows with high and low Estimated Breeding Values for mothering ability (EBVma), across two housing systems: Temporary Crated (TC) and Free Farrowing (FF). A secondary analysis within FF examined posture differences in relation to piglet crushing outcomes. Fifty-six multiparous sows (parity 3.3 ± 2.1) were monitored continuously from 48 hours before to 48 hours after parturition. Sow postures (lateral lying, sternal lying, standing, sitting, and kneeling) were classified using a YOLOv5m convolutional neural network. Behavioral data were analyzed in 3-hour blocks using generalized linear mixed models. Clear interactions between EBVma and housing system were observed. In the final 24 hours prepartum, FF High-EBVma sows spent a significantly higher proportion of time standing than all other groups (e.g., −9h to −6h: 0.54 ± 0.05 vs.; FF Low-EBVma: 0.37 ± 0.04, P = 0.04; TC High-EBVma: 0.26 ± 0.04, P = 0.003, and TC Low-EBVma 0.31 ± 0.04; P = 0.01), likely reflecting increased nest-building motivation. In contrast, FF Low-EBVma sows showed increased sternal lying at parturition (0.15 ± 0.03 vs. TC Low-EBVma: 0.08 ± 0.02, P = 0.08) and postpartum (42h–45h: 0.22 ± 0.04 vs. TC High-EBVma: 0.08 ± 0.02, P = 0.01), restricting udder access and potentially contributing to higher crushing risk. TC Low-EBVma sows exhibited consistently elevated sitting prepartum (e.g., −15h to −12h: 0.04 ± 0.01 vs. FF High-EBVma: 0.01 ± 0.003, P = 0.01), a behavior associated with restlessness in confinement. Within FF housing, Low-crushing sows displayed more prepartum standing (e.g., −15h to −12h: 0.41 ± 0.05 vs. High-crushing: 0.15 ± 0.04, P = 0.001) and less sternal lying postpartum (27h to 30h: 0.07 ± 0.02 vs. 0.19 ± 0.04, P = 0.004) than High-crushing sows. These patterns mirror the behavior of FF High-EBVma sows, and suggests that posture-based behavioral phenotypes may predict survival outcomes. In conclusion, posture patterns around parturition are affected by EBVma and affect piglet crushing risk, moderated by housing system. This study provides novel insights into the behavioral mechanisms underlying EBVma and supports the use of posture patterns as phenotypic indicators for genetic and management strategies aimed at improving piglet survival, particularly in FF systems.