Do you free feed or feed them individually? I thought my Megan, who is the biggest and alpha female, was eating as much as everyone else while free feeding too. However, I noticed her losing a little weight so I started watching closely and noticed at meal time she was only getting a few pieces of food and then watching everyone else eat. I didn't notice anything wrong before that because they weren't fighting over food or anything like that. I started fixing them a breakfast and a supper each day and I feed them in their kennels so I know everyone gets their fair share. Megan is now back to her 'normal' weight and we've had no more issues.
