How can cow's milk trigger my allergies and goat milk not?

Lucky: From an evolutionary point-of-view cows and goats are closely related. So the proteins in their milks are very similar and share many common allergens. 92% of children allergic to cow's milk are also allergic to goat's milk. Of course, 8% are not. That's why your child is lucky. Incidentally about 10% of children allergic to cow's milk are also allergic to beef.

Cow vs goat milk : The two types of milk are different allergenically. Only about a quarter of people who are allergic to cow's milk are also allergic to goat or sheep milk, according to a spanish research group who studied 58 children with severe milk allergies and found 15 had some cross-reactivity. http://www.ncbi.nlm.nih.gov/pubmed/22432882.