https://www.ncbi.nlm.nih.gov/m/pubmed/29371615/This fascinates me. It seems to suggest that feeding cows a modern diet of feed instead of having them graze like they're meant to makes milk more likely to elicit the development of an allergy.
I wonder so much how changes in food production have led to the jump in food allergies. My farmer dad thinks it has, and we'll eventually learn how.