Can I Make My Own Rat/Mouse Diet?
From the RMCA web site, June 2002, revised March 2005
Yes, but making a diet that is nutritionally complete for your rat or mouse is not trivial.
Rats are not terribly picky eaters and will eat just about anything. Mice are a little pickier, but both species, like humans, tend to love what is not good for them. Good nutrition is a primary determinant of good health. Good nutrition starts with a diet that meets all of the minimum daily nutrient requirements. The minimum daily nutrient requirements, the recommended daily allowances (RDA), of the rat are listed in the table below. The mouse RDA is very similar to that of the rat's. Also listed is the human RDA; both RDAs are normalized to a 10% moisture content.
We can see that the daily nutrient requirements of the rat are very similar to that of the human. Notable exceptions, however, are calcium, manganese, vitamin K, and vitamin B12 -- rats need 130%, 130%, 490%, and 290% more, respectively, of these nutrients than we do! Calcium deficiency results in stunted growth, osteoporosis, rear leg paralysis, and internal bleeding. Manganese deficiency results in birth defects, reduced food intake, stunted growth, skeletal deformities, and early death. Vitamin K deficiency results in major blood losses from minor injuries and spontaneous internal bleeding. Vitamin B12 deficiency results in stunted growth.
Obviously making a diet that is nutritionally complete for your rat or mouse should be taken very seriously. Let's see what it takes to build a nutritionally complete homemade rat diet. First we will build a dry grain mix composed of 1c Cheerios cereal, 1c Grape-Nuts cereal, 1c oats, 1/4c sunflower seeds, and 1/3c soynuts (roasted soybeans). The nutrient content of this homemade grain mix is listed below. Not surprisingly, this diet is very deficient in calcium, vitamin K, and vitamin B12. It is also deficient in vitamin D which most Americans get from fortified milk. (The fat content is rather high as well, but here we only address meeting the minimum nutrient requirements.)
Now we must take care of these deficiencies. The calcium, B12, and D deficiencies are relatively simple to take care of as these nutrients are available as OTC dietary supplements. For every 50g of this diet consumed (a typical daily consumption for a 500g rattie), approximately 250 mg calcium, 2.5µg B-12, and 50IU D will need to be added daily to the diet in the form of supplements. The vitamin K deficiency, however, is not so easily addressed, as vitamin K is available only by prescription. Dark green leafy vegetables are an excellent source of vitamin K, however, and, for example, a viable way of getting the 50µg vitamin K/day needed for every 50g of this diet consumed would be to give each rattie one brussel sprout every day.
Finally we are at a point where we MAY have a homemade diet suitable for our little rat and mouse friends-- a diet which meets all of their minimum daily nutrient requirements. Of course, that's ASSUMING they eat ALL the stuff we laboriously calculated in. In addition to just meeting the minimums, there are many, many other details that one must consider when attempting to build a COMPLETE and BALANCED staple diet for our rats and mice. For example, many vitamins and minerals interact with each other, and so relative ratios of nutrients are also very important and must be considered. Clearly, making a diet that is NUTRITIONALLY COMPLETE for your rat or mouse is not trivial; it's certainly not just a matter of throwing a bunch of "healthy" things together.
If complete and balanced nutrition is your top priority, always start with a commercial rat/mouse diet, one formulated by nutritionists, specifically for rats and mice, as their staple diet. "Staple" means at least 50 wt%. Then add a variety of other un- or lightly-fortified foods for fun and variety. Commercial rat/mouse foods are heavily-fortified for the specific, complete, and balanced needs of rats and mice, but large intakes of other heavily-fortified foods like dog food or Total cereal can easily throw off this balance. For this reason, try to limit the total intake of other heavily-fortified foods to no more than 10 wt% of the diet. Following these general guidelines, you can be sure your furry friends are getting a complete, balanced, AND enjoyable diet.
Nutrient Requirements of Laboratory Animals, Fourth Revised Edition
USDA RDA (RDI)
USDA Nutrient Database