Which of the following is a sign of mastitis in sows?

A sign of mastitis in sows is painful swelling. Mastitis is an infection of the mammary glands, which can cause significant inflammation and discomfort in the affected area. When mastitis occurs, the tissues around the mammary glands swell, leading to pain that can be observed when the sow is touched or if she displays protective behavior toward her teat area. This painful condition may also lead to changes in behavior, such as reluctance to allow piglets to nurse or changes in nursing behavior.

In contrast, increased appetite is generally not associated with mastitis; instead, sows may exhibit a reduced desire to eat due to discomfort. A stable temperature typically indicates that there is no significant infection or systemic illness, while bright eyes are usually a sign of good health; neither provides evidence of infection or inflammation in the mammary glands. Therefore, the painful swelling stands out as a direct indicator of mastitis in sows.