Melissa, why do you want to give any kind of milk? Are you not bf at least a little?
The problem with GM is very low folate so if you do give it in significant quantities, Nanny formula from NZ is better than goat milk. Casein has already been mentioned. Third problem - no iron. Both iron and folate deficiencies can lead to anemia. Nanny not available - may be Floradix with iron liquid (expensive) as a supplement to goat milk?
Fourth concern - why give it straight? If you ever decide on goat milk, start with youghurt or goat cheese, both have gone through fermentation process and are more easily digestible. If your child tolerates fermented products well, then you may decide to move on to milk.
I gave my dd1 all of the goat products incl milk before she turned 1 (without problems and in insignificant quantities), but with her little sister, I was more educated and held out.