As group housing becomes more common in the swine industry, researchers have studied ways to reduce aggression when unfamiliar sows are first mixed. However, Kansas State University researchers say that less attention has been given to another period of concern: the final weeks of gestation.
Field reports have indicated increases in vulva and body lesions as sows approach farrowing in group housed sows. Researchers say increasing discomfort and changes in a pen’s social dynamics as sows are moved to farrowing facilities could contribute to the behavior.
Beyond animal welfare concerns, late-gestation aggression may also create difficulties during farrowing.
K-State researchers and partners from the University of Missouri, Carthage Innovative Swine Solutions and the National Pork Board recently evaluated several approaches to better understand how producers might manage this issue under commercial conditions.
The studies evaluated strategies ranging from increased feed allocation, soluble fiber inclusion, dietary magnesium, tryptophan, and environmental enrichment. Researchers monitored such aggressive interactions as pushing, mounting, and biting while also measuring lesions, sow performance, and indicators of physiological stress.
While there may not be a single answer for managing aggression in late gestation. The studies do provide researchers and producers with a clearer picture of how nutrition, feeding behavior and the sow’s environment interact during the weeks approaching farrowing.
One study involving nearly 1,500 sows and gilts examined whether increasing feed allocation or adding soluble fiber through soybean hulls during the final two weeks of gestation could influence aggression.
Researchers theorized that providing more feed or soluble fiber could increase safety and potentially reduce aggressive interactions.
“Sows receiving increased feed or added fiber had fewer aggressive bouts during portions of the early morning, particularly around feeding stations,” said Cooper McAuley, K-State doctoral candidate who conducted the trial.
The findings suggest that feed allocation and fiber may influence feeder-related aggression.
Researchers also tested whether adding magnesium to late-gestation diets could provide a calming effect. The study included 952 sows and gilts, with half receiving a control diet and half receiving additional magnesium.
While magnesium supplementation reduced sow fallout during late gestation and farrowing, it did not reduce aggression.
Tryptophan, an essential amino acid, was another potential strategy. Previous research suggested that additional tryptophan could reduce aggression when unfamiliar sows were mixed, but researchers wanted to determine whether it could have a similar effect during late gestation.
In the commercial study, increasing tryptophan did not affect aggressive behavior, sow performance or most physiological stress indicators. Researchers did, however, observe increasing vulva lesions as sows approached farrowing regardless of treatment, reinforcing the concern surrounding aggression during late gestation.
McAuley said one of the more interesting approaches came from something outside the feed formulation itself.
He said researchers provided pens of late-gestation sows with suspended molasses and beet pulp-based enrichment blocks. The blocks modestly reduced total aggressive interactions, with tendencies for reductions in aggression both near and away from feeders. The treatment did not affect litter performance or physiological stress indicators.
Swine producers, students, nutritionists and others interested in learning more about these trials and other current K-State swine research can attend the 2026 K-State Swine Day on Thursday, Nov. 19.
The event will provide an opportunity to dig deeper into research addressing challenges facing commercial swine production, including strategies researchers are evaluating to improve sow behavior and management.
