Taken from - The New Hedgehog Book by Pat Morris
We used four captive hedgehogs (3 females, 1 male) and fed them Pedigree Chum dog food diluted with crumbled dog biscuit, knowing this to be a good standard diet for hedgehogs. There was plenty of water for the animals to drink. On this diet the hedgehog's droppings were all firm and dark brown in colour. We then fed them only on bread and milk for ten days, and this resulted in green sloppy droppings. Back on Chum for a week and all was well again. We then tried bread and water for a few days, biscuit and water, and finally biscuit and milk. Each experimental period was separated by a short time with Chum from food. The milk diet certainly caused diarrhoea and green droppings, but this was at least partly due to excess fluid in the diet because even water mixed with bread (or biscuit) caused the droppings to be rather loose.
The results were the same for all four animals and it is clear that breadk and milk alone is not an ideal diet and does cause upset tummies. However, all four hedgehogs kept up a healthy body weight throughout the eight experimental weeks. Their weights dropped sharply over the weekends as they were not fed on Sundays, but recovered again the following week whether they were fed bread and milk or anything else.