The weight ratio between goats and cows is 1 to 10, which reflects in the chemical differences between the two milks, each intended to meet the needs of its own species.  
In goats protein chains are shorter compared to cow’s milk.  
Fat globules are also different:  in goats they measure 0.1 to 1 micron, while in cow’s milk the particles measure 3 to 10 microns.