I just switched my 12 year old Collie from Medical to Evo because I thought I would give her the best. She's been on Evo now for approximately 3 weeks (weaned her off the Medical slowly) and farts all the time. Not only that, but I got concerned because I noticed she hasn't been pooping. Then today there was a hard poop on the living room floor. After checking her out "down there" I discovered another hard poop stuck to her fur and she was a mess down there! I'm going to look for something else.