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So I have 2 Jacks, one is a 4 year old male (Rocko) and the other is a 11 month old female (Roxy). My question is why is my girl like a giant compared to my boy? They are both the slick hair breed and the only difference is he is black and white and she is brown and white. But she seems like a good 5-10 lbs heavier and is even built like bulkier than he is and we use to think he was a beefy little guy! Why is this?