Usually happens with any animal actually. The best way to introduce new food to any animal is slowly. Do one new thing at a time, so you know which might not have a good effect on them. Then when you do add a new item, mix it with their regular food, so it's not so much just new. Give the new item about 4-7 days before trying another new item. By the fourth day give or take the poop should be normal if the food item agrees with the animal.