While the adulteration surely didn’t help, I don’t think I’d trust pure milk from these cows, either:

Swill milk dairies were noted for their filthy conditions and overpowering stench both caused by the close confinement of hundreds (sometimes thousands) of cows in narrow stalls where, once they were tied, they would stay for the rest of their lives, often standing in their own manure, covered with flies and sores, and suffering from a range of virulent diseases. These cows were fed boiling distillery waste, often leaving the cows with rotting teeth and other maladies.