Milk contamination may occur in these ways: * Animal feces coming into direct contact with the milk * Infection of the udder (mastitis) * Cow diseases (for e

Milk contamination may occur in these ways: * Animal feces coming into direct contact with the milk * Infection of the udder (mastitis) * Cow diseases (for example, bovine tuberculosis) * Bacteria that live on the skin of animals * Environment (for example, feces, dirt, and processing equipment) * Insects, rodents, and other animal vectors * Unsanitary conditions in milk processing plant * Cross-contamination from dairy workers, such as contact with dirty clothing or boots Source as linked in another comment: https://www.cdc.gov/foodsafety/rawmilk/raw-milk-questions-and-answers.html https://www.cdc.gov/foodsafety/rawmilk/raw-milk-questions-an... From my reading raw milk can be contaminated inside and outside the cow from such a myriad of sources and while cramped industrial farming might increase the likelihood of contamination it doesn't remotely eliminate the risks. Also note pasteurization practices originated prior to industrial farming