What does OU-D mean on milk?
OU certified milk is not Cholov Yisroel unless identified as such on the label. In general, the OU follows the opinion of Rav Moshe Feinstein zt”l, and others, that government inspection of dairies is equivalent to a Mashgiach’s supervision, whereby the status of the milk from these dairies is halachically equivalent to that of Cholov Yisroel . This is due to government inspections that insure cow’s milk is not adulterated with other species of animal milk.
The OU-D insures that all vitamins added to the milk and the processing equipment are completely kosher.