Welcome to FDMB.
One of the complications is that the OM is high in carbohydrates. The Savory Select flavor is 17% carb and the regular OM is 21% carb. We consider low carb as under 10% and most of the folks here feed their cat a food that's in the neighborhood of 5% carb. This
chart contains information about most of the canned foods available in the US along with the nutritional values including carbs. If the amount of carbs is high, you will need larger doses of insulin to offset the impact of the food on blood glucose levels.
If you switch foods, please do so slowly. Changing over to a low carb food can drop the blood glucose levels and you will likely need to reduce your cat's insulin dose to prevent hypoglycemia.
Also, please get Ketostix at any pharmacy. Given Rocket was diagnosed with ketones, you want to be sure that they are not developing again. Testing for ketones (and home testing for glucose levels) is the best way to keep Rocket safe.
Another consideration is that Vetsulin is not an insulin that is recommended by the American Animal Hospital Assn for the treatment of feline diabetes. They recommend either Prozinc or Lantus (glargine). Vetsulin does not last for 12 hours. So you may see a drop in numbers during the earlier part of the cycle but the numbers will be high at pre-shot times. Both Lantus and Prozinc have a longer duration. You also do not need to wait after feeding your cat in order to give an injection. With Vetsulin, it's important to have food on board because it's a harsh insulin that can drop numbers fast. This is our
guide for Vetsulin. You may find it helpful however, I'd encourage you to talk to your vet about a different choice of insulin.