In the late 1800s and early 1900s, milk quality in the US was low due to factors like feeding cows alcohol production remnants, which pasteurization helped address.

“in the late 1800s a lot of cows and dairy farms were fed on swill what is swill the origins of that word are that it is from the grain production of alcohol it's the remnants the dregs of alcohol production so it's Grain water the used up grains from the production of alcohol pretty low quality foods and there were problems with contamination of milk in less than sanitary conditions at the turn of the century this being the 20th century the late 1800s early 1900s and in that case the pasteurization of the milk did appear to have some net benefits from a an overall Public Health perspective”