How many toes are guinea pigs supposed to have?

I have a guinea pig who has a 4th back toe that I just recently noticed. The other two have 3 on each back foot, he is short haired and average sized (just incase it matters) but he seems to have an extra on his back left foot, it isn't attached like the others it just hangs off slightly to the side. Does this mean hes inbred? Or should I see a vet about it? It doesn't seem to cause pain because I never noticed him laying off that foot or walking differently from the other two