My male boxer dog has swollen nipples, what do I do?

It is possible that this is nothing to worry about, but if it's accompanied by other symptoms you should take your dog to vet.Some possible other symptoms:

-trouble peeing or change in drinking habits

-redness or discoloration of the nipple

-pain

-he's lost weight, had a change in appetite, or slowed down

-green or yellow discharge from penis, or blood.

If you see any of these or the problem persists take him to vet. In a breed with as many potential health problems as boxers it's always better to be on the safe side.