There are two diets on my blog. One contains beef, one does not.
The diet that I feed Gizmo on a daily basis contains beef as a main ingredient. Reds do alright on beef, as they can digest it much more readily than the smaller species:http://www.thepetfox.net/2010/08/fox-fo ... -diet.html
The other diet I have, the "recovery" diet, is what I fed Gizmo after he gained a lot of weight when I was no longer permitted to walk him. It's lower-calorie than the other diet without losing any bulk, and is still nutritionally complete. I designed it for red foxes who had had their normal activity curtailed due to surgery or something similar, or red foxes that need to lose weight. This is also a preferable diet for smaller foxes who do not digest beef well. The primary meat sources in it are chicken and turkey:http://www.thepetfox.net/2010/08/fox-fo ... -diet.html
I have a third diet that I've designed, but I haven't posted it yet as I haven't gotten an opportunity to test it to see how Gizmo does on it. It's based on a more "natural" diet, and includes whole mice and rats (please note that the nutritional values for it were calculated from frozen feeders, as that's what I will be feeding Gizmo).
Right now, I can't test the diet, as I don't think my landlord would be too happy with me giving him whole prey while he's housebound. But once we move and he's got an outdoor enclosure again, I'll be testing the new mixture to see how he does on it. It'll probably be a year or so before I have it tested and ready to release.