The nutritious beta-casein protein in milk is either an A2 beta-casein or an A1 beta-casein. Grazeful herds produce only A2 beta-casein milk.   
 

Because A2 beta-casein is more similar to the proteins found in humans, it may be more easily absorbed by the body and digested than A1 beta-casein.
 

If you have difficulty digesting milk, you may find this difference allows you to enjoy milk again!