Have you ever dealt with a cat with food allergies?

A cat with hair loss from food allergies. Photo from Diagnostic Imaging Atlas.
My 12 yr old male cat was just released from animal hospital after a urinary blockage. He has a severe allergy to chicken (causes skin lesions and diarrhea) and the food they recommended, a Dissolution blend called S/D from Hill's Prescription Diet, has chicken in it as do most commercial cat foods. Is there any Urinary Tract Dissolution or Preventative formula out there that doesn't contain chicken? Thanks!
A cat with lesions on its head from food allergies. Photo from Diagnostic Imaging Atlas.
Proteins cause most food allergies. It's unusual for pets to be allergic to carbohydrates or fats. Considering all dog food allergies, two-thirds are caused by beef, dairy, and wheat. Dogs are also frequently allergic to soy, chicken, eggs, and corn. For cats, 90% of food allergies are caused by beef, dairy, and fish. Cats are also commonly allergic to lamb, wheat, chicken, and corn. A cat with a lesion on one toe pad from food allergies. Photo from Diagnostic Imaging Atlas.Cats may be allergic to different ingredients that may be found in commercial cat food including:Cats are not likely to be born with food allergies.
Dogs and cats with allergies are itchy. They itch because histamine is released when their immune system attacks the offending allergen. Areas of the skin that most often itch are ears, eyes, feet—even between the toes—arm pits, groin, and around the anus. This itching causes feet biting, head shaking, face rubbing, and bottom scooting. Some pets also bite or scratch their bellies. About 60% of cats that pull out their hair (barbering) and have bald spots (alopecia) have itchy skin from food allergies.No sex predilection has been reported for food allergy in dogs or cats. In some studies, no breed predilection was noted. In contrast, two studies found that certain dog breeds may have a risk for the development of food allergy: For dogs and cats, the most common sign of food allergy is itching and scratching. Other signs of food allergies are head and neck itching, miliary dermatitis, eosinophilic granulomas, swollen lymph nodes, hives, and conjunctivitis.For many pets, one of the best methods of diagnosing allergy is with a food elimination trial. Food elimination trials require pets to eat only special diets, such as the Hill's Z/D diet with all the components broken into such small segments they no longer arouse the immune system. After 3-8 weeks on Hill's Z/D, your pet receives one food with kibble for 3-8 weeks. If no symptoms occur, you know your pet tolerates this food. More foods are added one at a time. The difficulty with food elimination trials is that pets can have nothing else—no treats, bones, chewies, or flavored medications—during the test period.The most common clinical sign of food allergy is non-seasonal pruritus, which is usually generalized. Pruritus may also be primarily directed at the feet or ears. Very rarely, food allergic dogs with skin lesions but without pruritus have been reported. The most common primary dermatologic lesions are papules and erythema; common secondary lesions are epidermal collarettes (usually indicating a pyoderma) pyotraumatic dermatitis (“hot spots”) hyperpigmentation, and seborrhea. Clinical signs of food allergy have been reported in Cocker Spaniels identical to the idiopathic seborrhea associated with that breed. Food allergy as the underlying cause of idiopathic onychodystrophy (misshapen, splitting claws [nails]) has been reported in two dogs. Food allergy in cats may present as pruritus of the head and face, milliary dermatitis, or one of the manifestations of the eosinophilic granuloma complex.Nine ingredients frequently cause food allergies in cats. Cats affected by allergy or intolerance to foods develop itchy dry skin or skin rashes, particularly around the face and ears. If your cat spends long periods of time scratching at himself and there are no fleas or ticks present, cat food allergies may well be the problem.