A USDA study found several influenza A virus groups circulating in linked sow farms and nurseries across four US production systems.
Sampling across four production systems
The study, published in August 2025, followed sow farms and linked nurseries in four US production systems for as many as 14 monthly collection rounds. Researchers identified several influenza A genetic groups. Nursery samples included viruses related to those found at linked sow sites and others not detected there.
Differences within the same system
The results show variation within the production systems studied. Sampling only pigs with clinical signs gives a different picture from routine sampling across both production stages. The accompanying USDA photograph shows a sow and piglets from an earlier image collection; they were not part of the study.