Well i personally have never had any problems with keeping them together. But like any animal there can be problems keeping any different breeds/types together. Everyone is entitled to there own opinion on things but doesnt mean they are right . Thought i would reply as this is obviousley indirectly pointed at me funny how it has come up after my thread about my kids new pets . I have bred and kept rabbits and guinea pigs for years and family before me so not as if i dont know what i am doing also worked in a pet shop for years and never heard of a rabbit killing a guinea pig and they kept there breeding stock together mixed rabbits and guinea pigs