Noki has been eating Scooters left over wet food and we think he's allergic to something in it. He's licking the hair off his butt so he has to wear the donut. We know he's allergic to wheat but neither his dry food or Scooters wet food has any so we're guessing he's also allergic to the soy in the wet food. Trying to keep him from eating the leftovers and also switching it up with a different brand.
Indeed we noticed the litter box smells way less, the poop but pee as well. We went on BARF because he kept vomiting on dry food and now he only barfs hair balls. He sometimes still had trouble pooping, we now put a few drops of olive oil a day into his diet...works well. For treats we give him cooked and chopped chicken livers or shredded chicken breast, half warm. He loves cooked chicken and stays close when preparing.
Our little monster is the same about cooked chicken, if you have it you have obviously made a mistake, that is his food and while he is a gentle god he can also be a jealous god.
As for the fat, we have recently tried using fat from pork roasts, the fat cap is thick and soft so we can take a little of that and add it to his containers. I tried more refined fats, he will definitely eat butter, but he ends up missing the stop point and having loose stools if we use a refined fat.