I'm sorry to hear of this with your cat. High fiber diets aren't recommended for older cats as they decrease the energy density of the diet and decrease digestibility. Increasing the nondigestible fiber content of a senior diet by adding Miralax is smart as it should increase colonic motility and intestinal transit rate without altering the energy density or decreasing digestibility of the basic diet. Here's a chicken-based diet for the senior cat:
chicken, breast, without skin, cooked, 4 ounces
rice, white, long-grain, cooked, 1/2 cup
canola oil, 1 tbsp
salt substitute (potassium chloride), 1/4 tsp
bone meal powder, 2/3 tsp
salt, iodized (sodium chloride), 1/8 tsp
multivitamin & mineral tablet, kids complete, 1/2 each
taurine powder, 1000mg per 1/4 tsp, 1/4 tsp
Total kcal as prepared = 416 kcal which is the daily requirement of a 21 lb senior cat. You can refrigerate uneaten food for 3 days or freeze indefinitely while checking for spoilage.
Please respond with further questions or concerns if you wish.