- Normal hormonal changes: During the heat cycle (estrus), a female dog's nipples may enlarge and become firm due to increased hormone production. This is normal and should subside once the heat cycle ends.
- Pregnancy: If your dog is not spayed and has been in contact with a male dog, a hard nipple could be a sign of pregnancy.
- False pregnancy: A false pregnancy occurs when a female dog shows signs of pregnancy even though she is not actually pregnant. This can cause the nipples to become hard and enlarged, and the dog may also produce milk.
- Mastitis: Mastitis is an infection of the mammary glands, which can cause the nipples to become hard, swollen, and painful. Mastitis is most common in nursing mothers, but it can also occur in non-lactating dogs.
- Tumors: In rare cases, a hard nipple could be a sign of a mammary tumor. Mammary tumors can be benign (non-cancerous) or malignant (cancerous).
Whether or not a hard nipple in a dog is serious depends on the underlying cause. If you are not sure what is causing your dog's hard nipple, it is best to take them to the vet for evaluation.
The vet will be able to determine the cause of the hard nipple and recommend the appropriate treatment.