Dog is super gassy and is constantly biting/scratching angrily at her butt?

A trip to the vet first. This will help rule out if she has fleas or parasites. Some dogs are so allergic one flea bite will send them into a biting frenzy. just remember if you switch her to a grain-free food, the treats also need to be grain-free too. The top three things dog are allergic to is beef, corn and wheat. So No rawhides for your dog. For 2 months really just limit her food intake of different foods. Only feed her the dog food. It is than that you could introduce her to different things. If she has gas, an ahaa moment will occur and you will know what she is allergic to. You may have thought by feeding her the Purina lamb and rice food was a limited ingredient food. Look at the ingredients. Corn-gluten meal and whole grain corn are the 3rd and 4th ingredient. Now to fully understand most people would think that lamb was the number one ingredient, but this may not be so. Things are listed in order by weight. Meat has a lot of water in it, making it heavier than a meal Now they cook the meat. Now the dog food could have more corn than lamb or rice. You may think by buying those dog foods are more expensive but being a better quality you will not have to feed her as much. In the long not that much different, especially if only feeding one dog. Your guests will appreciate the change.