I rescued two guinea pigs from a pet store where someone had left them in their cage outside the store. They are adult males and I have had them for two weeks.I have them in a large pen 4'x3'.They were getting along great untill today I was going to brush one and it's rear end is all bitten.I washed it but I don't know what to put on the bites.It dosn't look infected .I have seperated them to other cages but this will be a problem as the cage they came with is small.Why did this happen and what should I DO? I have two other males who get along fine.(They are not with the new pair).