Postweaning or dry-sow mastitis is a common type of mastitis that affects one or a few glands. The prevalence among newly weaned sows is 10%–20%. Chronic mastitis is characterized by the formation of abscesses and granulomas in the mammary tissue, which are often seen at weaning or shortly after. A primary pathogen has not been identified. Bacteria commonly enter the mammary glands through teat wounds caused by the piglets’ sharp teeth during suckling, fights among aggressive weaned sows grouped in the same pen, or trauma associated with the particular anatomy of inguinal mammary glands of old sows.