Got milk? Is It fresh?

As a child, my parents always made sure that my brother and i had plenty of milk to drink. As a parent, i carried on that tradition for my children, except in a few cases. Many times i have purchased milk and it would not last until the expiration date, stamped on its carton. Why was this? This only occured at one particular store chain, in which the milk was purchased. It was the stores brand of milk, not the brand name. Question: Who’s fault was it for the bad milk? The Store, the milk producer, or the cow?