All orphaned animal babies are dehydrated from missing even a single meal from mom. With artificial feeding comes problems (like bloat) that can be a slow killer to any infant. Just like adults, giving pure water (let alone full-fat formula) to a dehydrated body will cause the stomach to swell instead of digest. If severe, it can even induce vomiting and further dehydration.
For dehydrated infants given formula, this has deadly effects as the body tries to quickly absorb the water content while leaving an undigested wad of curd that plugs the intestines, preventing digestion and causing a slow, painful death.