The road to hell is paved with good intentions and the river that runs alongside is filled with goat’s milk.
Vast numbers of neonatal wildlife have died with bellies full to bloating and faces covered with goat milk. Deer, mice, squirrels, raccoons, opossums, ducklings, starlings, porcupines, iguanas, puppies, kittens, the list goes on and on. All have come into the hospital not doing well and the common denominator is they have been living on mostly goat’s milk for a week or so.
Why is this the case? Many people say that is easier to digest and that is true, for humans. Goat’s milk has slightly less lactose in it than cow milk and the fat is in smaller globules so it is in general easier to digest. But neonatal mammals have plenty of lactase to digest milk and non-mammals can’t digest it no matter how little there is. Adult mammals do not produce lactase either and so they can’t break down what little lactose is present.
The nutritional content of milk from various species also differs and is tailored to ensure that the species the milk is intended for gets the maximal benefit from it. They all differ in calories, fat, protein, carbohydrates, and vitamins/minerals. As an example, cow milk is about 4% fat depending on the breed, deer milk is around 20%, and goat milk is about 3.5%. So when a baby deer is getting goat’s milk it is not getting enough calories and will slowly starve. For non-mammals and adults the milk can cause very severe diarrhea which dehydrates them and prevents them from absorbing any nutrients at all.
So what do baby animals that do not have a mother eat? Milk replacement formula for their species. There is milk replacer for just about any species you can think of from llamas to squirrels and even rhinos. For animals like reptiles and birds there are non-milk formulas they can eat that are made for their particular physiology.
Another problem with feeding babies is that people have all kinds of ideas about how much, what temperature, and how often to feed. I once had a woman who told me she knew when to stop feeding her baby macaws when the food started pouring out of their mouths. A kitten owner syringe fed so much milk that it began pouring out of the rectum because the GI tract was overloaded. Animals are often over or underfed and they do not do well either way. Another common issue is food being aspirated into the lungs of the animal from incorrect technique. Once this happens they develop severe pneumonia and almost all die. This happens in baby birds often. Yet another problem is food that is too hot. Birds can get severe crop burn and other animals can have their mouths and esophaguses burned so badly that the tissue sloughs and leaves necrotic holes.
So what to do if you find a baby animal? Call a veterinarian or a wildlife rehab facility. They have all of the tools and training to do the job properly and ensure the animal is healthy.