Baby rabbits should not be fed cow milk. Rabbits have delicate stomachs and cannot vomit. Cow milk contains high levels of substances that cannot be digested by rabbits.
The best milk for baby rabbits is the special formula called Kitten Milk Replacer (KMR). KMR contains whey protein, probiotics, vitamins, prebiotics, fat, and carbohydrates.
Apart from KMR, another type of milk that you can feed your baby rabbit is goat milk. But you must be cautious with goat milk. There are many goat species and the content of their milk may vary significantly.
Baby rabbits cannot be fed arbitrarily because of their sensitive stomach. The volume of feed to give them and the frequency of feeding are limited. Rabbits require infrequent feeding with small volumes of feed.