A new study from researchers at Christian-Albrechts-University of Kiel, the Chamber of Agriculture of North Rhine-Westphalia, and the University of Veterinary Medicine Hannover, published in Frontiers in Animal Science, tackles exactly this question under conditions that most previous work has avoided: a genuine commercial farrowing barn, complete with slatted floors, manure scrapers, routine cross-fostering, and temporary crate confinement. Over one full year of data collection, the team followed 221 farrowings from 141 sows across 11 batches, assigning each to one of three treatments. Two groups received organic nesting material delivered in wall-mounted racks: one got grass hay, the other long-stemmed barley straw. The third group, serving as a control, received only a jute bag attached to the crate, which represents the minimum enrichment standard currently mandated under German legislation.

The choice of materials was deliberate. Straw and hay are cheap, widely available, and explicitly endorsed by the European Food Safety Authority as functionally appropriate nesting substrates, making them realistic candidates for adoption on commercial farms. Jute bags, by contrast, stimulate some manipulation but lack the structural properties of a true nest-building medium. Earlier studies had mostly compared the presence versus absence of nesting material, leaving open the possibility that any manipulable object would do. By pitting two natural substrates against a minimal enrichment control, the German team could test a sharper hypothesis: that the functional characteristics of the material, not merely its presence, determine whether sow welfare and piglet survival improve.

The results, published on 6 October 2026, are striking in their specificity. During the first three days after birth, the odds of a piglet being crushed were 46 percent lower in the straw group than in the jute bag control, a statistically significant difference. Hay, despite being a natural material, showed no significant advantage over the control. By the end of lactation, the treatment effects had faded, with no significant differences in total crushing losses among the three groups, but the early window, the period in which piglets are most vulnerable, told a clear story. In the straw group, only 3.51 percent of live-born piglets were lost to crushing in the first three days, compared with 4.68 percent in the hay group and 6.52 percent in the jute bag group.

To understand why straw outperformed both alternatives, the researchers turned to an increasingly powerful tool in modern animal science: computer vision. Sows were filmed from overhead cameras mounted roughly 3.2 meters above the pens, recording at 2560 by 1920 pixels and 30 frames per second, with infrared illumination enabling continuous monitoring through the night. The team then deployed two independent YOLOv11 deep learning models, one performing object detection to locate the sow and classify her posture directly within the frame, and a second performing image classification on the cropped bounding box to independently verify the posture. The four postures, standing, sitting, lying, and lateral lying, were collapsed into two functional states, active and resting, and a posture change was defined as any transition between them.

The consensus-based approach proved remarkably accurate. When both models agreed on a posture prediction, the combined pipeline achieved precision, recall, and F1 scores between 0.92 and 0.93, and the mean absolute error in counting posture changes across 500 manually annotated reference videos was just 0.44, compared with 5.19 or higher for either model alone. Short-term fluctuations lasting less than five seconds were filtered out to prevent transient misclassifications from contaminating the data. This level of automation matters because posture changes have traditionally been counted by hand from video footage, a process that is slow, expensive, and difficult to standardize across studies and farms.

The behavioral data revealed the mechanism behind the survival benefit. Sows provided with straw showed approximately 28 percent fewer posture changes during the first 72 hours after the birth of the last piglet than sows in the jute bag group, with median counts of 128 versus 160 transitions. More importantly, the statistical models established a direct link between sow movement and piglet fate: every additional 10 posture changes increased the odds of crushing by roughly 8 percent. When posture changes were included as a predictor in the crushing model, the material effect itself disappeared from significance, suggesting that straw protects piglets not through some mysterious property but by calming the sow, reducing her restlessness, and thereby reducing the dangerous rolling and lying-down movements that trap piglets beneath her body.

The contrast between straw and hay is perhaps the most scientifically interesting finding. Both are natural, organic substrates, yet only straw produced a measurable reduction in crushing risk. The authors attribute this to structural differences: straw’s coarser, more persistent texture provides stronger tactile feedback during manipulation and remains accessible on slatted floors for longer, whereas finer hay may disperse more easily and satisfy the sow’s nest-building motivation less effectively. This aligns with earlier work showing that hessian sacking, although it stimulated nest-building in crated sows, failed to deliver the improvements in farrowing outcomes that straw provides. Not all enrichment is biologically equivalent, and the specific functional properties of a material, its structure, persistence, and the way it responds to rooting and pawing, appear to determine whether the sow’s deeply motivated prepartum behavior is genuinely fulfilled.

The study also carries practical weight for an industry in transition. Germany has recently amended its Animal Husbandry Regulations to restrict farrowing crates, and several countries are moving toward systems that give sows greater freedom of movement. Yet producers consistently identify the farrowing period as the most difficult stage to manage without confinement, precisely because loose sows pose a higher crushing risk to their litters. The present findings suggest a pragmatic middle path: even in systems with temporary crating for roughly 9 to 10 days around farrowing, providing structured nesting material such as long-stemmed straw through simple wall-mounted racks can meaningfully reduce early crushing losses without requiring structural renovation, without interfering with slurry management, and with only modest additional labor for daily refilling.

There are caveats worth noting. The posture analysis was restricted to a subsample of 50 farrowings due to computational and practical constraints, and routine cross-fostering on the farm, which was not fully documented, may have introduced minor uncertainty into litter composition during the early postpartum period. Crushing losses were therefore calculated relative to the number of live-born piglets per litter. Individual variation among sows was also substantial, with some animals barely touching the provided material and others nearly emptying the racks, and differences between individual sows accounted for the largest share of variation in material use. Still, the overall pattern is consistent and mechanistically coherent: a calmer sow is a safer sow, and the material that best satisfies her nest-building drive, long-stemmed straw, delivers that calm. As automated monitoring technologies mature and regulatory pressure to phase out crates intensifies, the humble bale of straw may prove to be one of the cheapest and most effective welfare interventions available to modern pig production.

Subject of Research: Effects of nesting material type on piglet crushing risk and sow posture changes in commercial farrowing systems with temporary confinement

Article Title: Effects of different nesting materials on crushing risk and sow posture changes in a farrowing system with temporary confinement

Article References: Wahmhoff, J., Wutke, M., van Asten, A. L., Kemper, N., & Traulsen, I. (2026). Effects of different nesting materials on crushing risk and sow posture changes in a farrowing system with temporary confinement. Frontiers in Animal Science, 7, Article 1960568. https://doi.org/10.3389/fanim.2026.1960568

Image Credits: AI Generated

DOI: 10.3389/fanim.2026.1960568

Keywords: sow welfare, piglet crushing, nesting material, straw, farrowing crates, nest-building behavior, computer vision, YOLOv11, posture changes, animal welfare, pig production, pre-weaning mortality