Hi Karen,
As a general rule, FDMB advocates testing before
every dose of insulin (the preshot test) to make sure that it's safe to actually give the dose. (Note: no food for kitty in the 2 hours prior to preshot BG test - UNLESS he's already running low and needs the food to keep numbers up!) Also for safety we recommend getting at least one BG test per day around expected nadir time (the 'mid-cycle' test performed during the period when the insulin dose's effect is at its strongest) to check that the current dose isn't taking the kitty too low.
As you've seen on Dr. Pierson's site, it's vital for safety to monitor more closely when changing to a lower carb food. You've already done really well with the food changeover and dose reduction BUT with the lower carb load it is possible for BG levels to continue improving quite substantially for some time
after the switch to lower carb food change has been completed (pancreas gets more of a chance to rest and may start producing more insulin). Regular testing will help you build a picture of what's going on in Rocky's body and you'll be able to respond promptly to any change in his insulin needs.
Novolin N typically has a fairly fast, hard onset early in the cycle. The FDMB guide for this insulin recommends leaving a good window of time between the feed after the preshot test and administering the dose of insulin (c. 1 hour). With the lower carb load in Rocky's new food it's even more important to leave a bit of time so that there will be sufficient glucose in his bloodstream ready for the insulin dose to get to work on. For the time being - and as best your situation will permit - I'd suggest getting BG tests quite soon after the dose is administered (e.g. +1 and +2 hours after the dose is administered), plus a BG check around the expected nadir time for Novolin N (see guide below). If you see a significant drop in BG at +1 or +2 it will give you an early warning to monitor BG closely for the next few hours to make sure that Rocky doesn't go too low.
Tip: A lot of kitties tend to run a bit lower during the evening. A 'before bed' BG test is always a very good safety measure, and is possibly even more important when the carb load in the diet has been reduced.
The following forum sticky will help you to learn more about Novolin N plus lots of general guidelines on treating a cat with insulin plus more specific guidelines on home testing and feeding schedules for kitties receiving Novolin N:
FDMB Beginner's Guide to Novolin/Humulin/NPH
Insulin doses are measured in International Units (IU). Just to avoid confusion for members reading this thread (myself included!) can you please confirm that you are giving Rocky 2 UNITS of insulin twice a day.
I am thinking that might be a good plan!
Know the feeling well.

Obviously you'll still need to make sure you have full veterinary support for Rocky, but we will do all we can to support and assist you both. When vet shopping, try to find one whose style is more collaborative than prescriptive. A good working partnership with one's vet makes a world of difference.
I am pleased that Rocky is already feeling the better for the food change. Fingers and paws crossed for further improvements in the very near future.
Mogs
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