I have a young male Border Collie and a somewhat bizzare question. One of his testicles is somewhat larger than the other. The vet told me not to be alarmed, but could that in any way affect his "maleness?"
This is perfectly normal (in humans and dogs). It won't affect his maleness in any way. (It's actually probably not a true size difference in the testicles but in the amount of tubules that have descended into the scrotum).