Wow, 3 is a great age!! I hope to have rats get that old some day! But unfortunately, loss of weight and muscle is quite normal and typical, especially on their back and backend, where you'll start to feel their spine. Give him plenty of high calorie and protein foods such as oatmeal, scrambled eggs, cheese and nutristat or nutrical. Mine love to have their diet suppliments with Boost or Ensure as older ratties. Lots of love and attention is what they crave the most at this point in their lives... I'm glad he'd getting to be your shoulder buddy now!
