Ubiquitin, Benignuman, correct me if I am wrong but I believe that a kosher liquid mixed with a nonkosher liquid has a much less stringent rule than the nonkosher unwanted taste being nullified in 60. I believe it is 1/6. Also, I believe I heard we do not have to worry that perhaps our particular container that we bought in the store, is nonkosher due to unfortunate coincidences which caused it to have a percentage of the nonkosher liquid larger than 1/6 (thus no bitul): given that the milk for sale is intended to be mixed at the processing plant e.g. for pasteurization, as long as the majority of USDA milk is kosher enough, we do not have to worry about a specific container. Again please correct me if I am wrong.
Many cows get their stomach punctured, it is a routine practice, but there is a high turnover of milking cows and young cows have not yet needed the procedure.