The block food expires after 6 months. I know there are people that feed hog feed, Blue Ribbon is the name. If you have a chance, check out the ingredients of whatever feed you do decide on. Rat's cannot digest alfalfa, so thats a big no no. Again, I say if you can print a copy of the ingredients to Purina's Mazuri or Harlan Teklad Global Diets, and try to get the closest match in protein, fiber, and ingredients, you should be off to a good start.