Which of the following is not a sign of heat in farm animals?

The option that is not a sign of heat in farm animals is "udder enlargement". Heat, also known as estrus, refers to the period when a female animal is receptive to mating. During heat, farm animals may exhibit signs such as restlessness, increased vocalization, decreased appetite, and a desire to be mounted by other animals. However, udder enlargement is not typically a sign of heat in farm animals. Udder enlargement usually occurs during pregnancy or after giving birth, when the animal is producing milk.