I took in a stray pregnant cat last August after she gave birth under my pool deck. Also took in her four kittens. When she was done nursing in Oct, she weighed about 12.5 lbs. Today, she weighs 22.2 lbs. She really doesn't eat a lot but I had been free-feeding dry food since I had 14 cats (I recently lost 2 of my 18 year olds, so I currently have 12). This mother cat (Sassy) was then spayed in Dec and she weighed in at 14 lbs. When she went back for her stitches re-check, she weighed almost 16 lbs. I took her to the vet 2 weeks ago to check for any medical reasons causing this. They did a full blood panel and thyroid and every thing looks completely normal. Sassy was put on the Hill's Metabolic diet and it's too soon to see any results, but I was wondering if anyone could give any insight on what might be causing this weight gain. My vet says some cats are just inclined this way since all her tests results were negative--just consuming more calories than she's burning. I'm trying to get her to move more but with 12 cats in the house, her kittens interfere with her having any play time. I've attached a picture of her in Sept when she was still nursing and a picture from now. Thank you in advance.