Shailoh of the Week by Rabbi Zvi Nussbaum
Rabbinic Coordinator, Kosher Hotline Administrator for the Orthodox Union
Jews are only permitted to drink milk that has been supervised to ensure that it was not altered with milk from non-kosher species or with non-kosher ingredients.
In some countries, the milk is known to be altered with fat. In the U.S., many Jews rely on the leniency of Rav Moshe Feinstein, that government inspectors can be relied on to supervise the milk. The reason for this is because the U.S. government has strict regulations, and there are inspectors who uphold these laws. In other countries, the laws might be more lenient, or the inspectors can be ineffective.