Have you tried this....
Nutri-Cal is a high-calorie palatable dietary supplement used for stressed or debilitated pets, pets suffering from illness, surgery or whelping, aging pets or picky eaters, who need increased caloric and nutritional intake.
Benefits:
Added nutrition for dogs and cats
Provides extra energy for active dogs
Good for picky eaters good taste and can place the recommended amount of gel on your finger, on your pet's paw, or can mix with food
Can be given to pregnant or ill pets
How it Works:
The Nutri-Cal formula contains vitamin A, D & E, Phosphorus, Thiamine, Calcium, Manganese, Iodine, Potassium, Iron, Folic Acid, Riboflavin and other essential ingredients, and provides an additional 338 calories per feeding.
This diet has been specially formulated to assist in the management of stress and anxiety in cats. It provides nutritional support for cats in stressful situations. It will also help with stress related digestive and skin disorders. This diet is formulated with milk protein hydrolysate and supplemental tryptophan and nicotinamide, which create a calming effect. This diet should be fed for a minimum of 2 weeks prior to encountering a stressful situation and it may take up to 12 weeks to see a response in high stress cats already in a stressful situation. This diet comes as a dry formula.
I feed my old cat a C/D diet for her urinary tract that has added tryptophan for her stress levels. Since she’s been on it her appetite has been wonderful and her health has improved a lot. I’d ask your vet if they think it’s an option.