Dear Reggie Rat: My rat, Seymour, has little bumps on his underside that would look like nipples if he were a female. One of the little bumps is attached to a firm, lumpy mass. What are the little bumps and the larger mass?
Reggie Responds: Male mammals, including rats and humans, have nipples and mammary (breast) tissue. So it’s likely the little bumps you see are Seymour’s nipples.
Males also can develop mammary tumors, and it’s possible the larger mass is a tumor.
Mammary tumors occur more often in females, though up to 16 percent of cases involve males. Mammary tumors grow rapidly, becoming quite large in weeks.
Research shows that rats offered free access to food have a higher incidence of mammary, pancreatic and pituitary tumors, compared with rats fed restricted amounts of the same diet.
Most mammary tumors are benign, but 20 to 25 percent are malignant. These cancers spread to other parts of the body slowly, so surgical removal of the tumor is the treatment of choice.
Early spaying decreases risk of mammary tumors in female rats. Dietary restriction to prevent obesity also helps lessen tumor incidence.
Have your veterinarian examine Seymour to determine what his mass is and recommend treatment.