We've had our 2 lovely female guinea pigs for 7 weeks now. They're in an indoor hutch and have been lovely together, no problems at all. Today we put them in a new outdoor hutch. Within half an hour they were squealing like mad, I went over and they were fighting each other 
Nasty, up on their back legs biting each other, real fighting. We separated them and have now reintroduced them back together in their old indoor hutch. They stay at opposite ends to each other but every now and then keep fighting. They clatter their teeth then the fight starts. What can I do? They were absolutely fine til then went outside, now they can't stay together 