If your bacteria bed is still alive, you should see practically no change in ammonia or nitrite after adding any ammonia source whether it be food or dead fish or shrimp. Usually, it takes about 3- 5 days ( depending on the size of the tank and amount of ammonia source) for ammonia to start showing up from disintegrating meat. If you go that route, I would check ammonia daily after introduction for the next 5-7 or 8 days and if there is no spike in ammonia, you can safely assume that your bacteria bed is functional and ready for livestock. Just make sure you don't over add stock at one time.
If you see a rise in ammonia, continue to monitor until the ammonia goes back to 0 and start checking nitrites once the ammonia starts to fall. Once both ammonia and nitrites have returned to 0, you can start adding more stock. Keep in mind that the bacteria bed is a living "organism" that increases and decreases in size with the amount of ammonia present. Once the nitrites have returned to 0, don;t wait too long to add more life to the tank to keep the bacteria bed going.
Hope this helps