A number of years ago, while listening to one of R’ Schachter’s Shiurim, I came away with the distinct impression that he had a serious issue in regards the Kashrus of any Milk in the USA because of the prevalence of Halachically damaged milk cows aka Treyf cows.
I discussed the issue with Rabbi Mordechai Gutnick of Kosher Australia and he advised me that the veterinary procedures extant in the USA were not germane here in the same way on account of the different feeding practices which obviated the potentially Treyf inducing condition common in the USA.
I also asked Rabbi Tzvi Telsner Dayan of of the Chabad Yeshivah Shule in Melbourne whether in light of Rav Schachter’s views, there was a problem with Chalav Yisrael in the USA. Rabbi Telsner claimed that the conditions in Chalav Yisrael production in the USA were much better than the general USA dairy industry and did not have this problem.
To understand this issue, please see the following article
[hat tip Moshe]