After 0/2 days of dog breeding/kloc-0, the pink nipple may be a normal physiological change, and there may also be some health problems. The following are possible reasons:

1. Pregnancy: The change of nipple color after dog mating may be a sign of pregnancy. When a dog is pregnant, the nipple will become more congested and the color will become lighter or pink.

2. Hormone changes: After dogs mate, the hormone level will change, which may lead to the change of nipple color. This is a normal physiological reaction, and there is usually no need to worry.

3. Mastitis: Pink nipples may also be one of the symptoms of mastitis. Mastitis is an infection or inflammation of breast tissue, which may lead to nipple color change, swelling or pain.

4. Other health problems: The pink nipples of dogs may also be related to other health problems, such as inflammation, infection and trauma.