Female dogs are most likely to be affected by swollen nipples due to the nature of their mammary gland. Extra precautions must be taken if swollen nipples are observed in dogs. Swollen nipples may indicate an infection or a life-threatening medical condition such as cancer. Swollen nipples in dogs may be caused by:

Swollen nipples in dogs is a common sign seen in mastitis. Mastitis occurs when there is an infection of the mammary glands. Mastitis can occur in female dogs who are in the process of nursing. In mastitis, the dog's mammary glands become swollen and painful. The milk is toxic in affected nipples. Mastitis tends to occur during the first 2 weeks after delivering puppies. If any changes in your dog's health are noticed, it is essential to contact your veterinarian for immediate consultation. Infections may spread rapidly and become fatal if left untreated. There are two types of mastitis – acute septic mastitis and galactostasis. In acute septic mastitis, bacteria enters the mammary gland, which creates a painful infection. In galactostasis, milk accumulates in the mammary glands which creates a swollen nipple. Common symptoms of mastitis in dogs are as follows:

Another condition which can result in your dog having swollen nipples is a mammary gland tumor. Mammary gland tumors commonly affect female dogs. A mammary gland tumor occurs when there is a mass growth near the nipples. The tumor can be either hard or soft and can eventually develop into an abscess. Mammary gland tumors can differ in size and location and can vary in colors such as red or purple. If you observe any bleeding near the swollen nipples, it is likely that your dog has developed an advanced cancer and must be seen by the veterinarian immediately. There are numerous types of mammary gland tumors which range from benign to malignant. Benign tumors usually take time to grow and are often smooth texture. Malignant tumors will usually have an irregular shape with rapid growth.

If your dog experiences swollen nipples as a result of mastitis or a mammary gland tumor, it is essential to seek immediate veterinary assistance. Mastitis occurs when bacteria enters the mammary gland. Bacteria can enter through various channels, increasing the risk of her becoming septic. A contaminated environment can also cause bacteria to seep through and enter your dog's body. Scratches from the puppies can also invite bacteria inside. Mammary gland tumors can develop through a variety of factors such as environmental factors, or hormonal situations. Your dog is most likely to be at risk for mammary gland tumors if she has experienced heat cycles in her lifetime, or was spayed at a later age.  

Your veterinarian may retrieve a sample of milk from the affected nipple. The milk will be assessed for any pus and bacteria. Your dog may undergo a complete blood count to determine the severity of the mastitis. An ultrasound may be suggested in order to locate any tumors which may be hidden from sight. If your dog is experiencing acute septic mastitis, your pet may be prescribed antibiotics and compressions to be applied to the swollen nipples. If your dog is experiencing galactostasis, your dog may be prevented from any water intake for half a day in addition to a withholding of food for up to 24 hours. This might be dangerous in the wrong situation, so would only be done under veterinary advice.  

For a mammary gland tumor, a biopsy would be used to diagnose mammary cancer in your dog. A sample would be sent to the lab to determine whether the tumor is benign or malignant. Other tests such as ultrasounds and x-rays can help determine how far in the body the cancer has reached. If your dog is diagnosed with cancer, the most effective treatment is surgery. The tumor would be removed in order to prevent regrowth. Chemotherapy may be recommended if the cancer is widespread and in advanced stages.

Prevention of swollen nipples in dogs starts with monitoring your dog's health. Examine your dog's teats on a daily basis and record any scratches to the area. Since mastitis usually occurs when your dog has puppies, ensure to keep the puppies' nails clipped. Clip any hair obstructing your dog's nipples to maintain cleanliness. In order to discourage over-usage of the nipples, it is recommended to encourage the puppies to nurse from all of them. If your dog has received surgery due to a mammary gland tumor, your veterinarian will set up an appointment to check how your dog has been healing. It is important to continue to monitor your dog for any signs of tumor growth. It is highly recommended to also check over your dog from ears to paws to catch any discrepancies.

The cost of medical conditions such as mastitis or a mammary gland tumor can vary depending on your location, your veterinarian's rates, and the severity of your dog's condition. Mastitis treatment ranges anywhere from $200 to $2000. Veterinary care for a mammary gland tumor is significantly more expensive due to the intensive treatment needed to help your dog recover. Medical care for a mammary gland tumor can range from $900 to as high as $15000. However, the average cost of treatment for a mammary gland tumor is $5500.