When a mysterious, rampant disease began killing infants in New York City in the 1850s, there were a lot of theories about what was really happening. The cause of the epidemic - it turned out - was milk. The Swill Milk Scandal of 1858 was discovered by a journalist who investigated the deaths, traced them back to tainted milk produced by poisoned cows. Much like the way John Snow mapped out cholera in London during the same decade, Frank Leslie's Illustrated Newspaper revealed the horrors of milk production and how it was killing people.
Swill milk was produced by swill cows - bovines fed the run-off, mash, and swill from nearby whiskey distilleries. The cows were kept in horrible conditions and abused, ultimately producing milk full of runoff and bacteria. Sold cheap and marketed as pure, "swill milk" wasn't banned until almost a century after the deadly events of the 1850s. However, the tragic scandal did create an awareness of food safety in the United States.
In 1857, Over 8,000 Infants Died From Drinking Swill Milk
Distilleries in or near large cities... an intolerable nuisance and curse... wherever they exist, their slops will furnish the cheapest food for cows, the milk from which is more pernicious and fatal to infant health and life than alcohol itself to adults... So long as distilleries are tolerated in cities, cow stables will be their appendages, and the milk, fraught with sickness and death, will still perpetuate mortality...
Many lower and middle class families at the time didn't have a lot of choice when it came to giving their kids the milk because it was the only affordable option for them. It's estimated that 50 to 80% of the milk consumed in northeastern cities was swill milk.
Because There Were So Many Other Diseases In The City, It Took Time For People To Realize What Was Happening
During the 19th century, infant mortality was on the rise in New York City. Diseases like cholera and typhoid were a part of everyday life, as was infant death. When children began dying from drinking swill milk, there was little reason to believe that anything was different from the status quo. Most weren't even aware that the deaths were happening because of the milk, as all of the other mortality causes seemed like explanations.
Swill Cows Produced Discolored Milk
The milk from swill cows was thin and devoid of enough fat to be used to make butter. It often "had an unnatural, bluish tint," so sellers added flour, starch, or plaster of Paris to make it thick and appear white.
The "Swill Milk," as it is most appropriately denominated - that bluish, white compound of true milk, pus, and dirty water, which, on standing, deposits a yellowish, brown sediment, that is manufactured in the stables attached to large distilleries by running the refuse distillery slops through the udders of dying cows and over the unwashed hands of milkers...
The cow's treatment and diet gave them an odd disease. Their lungs ulcerated, and their milk secretion increased with it. This led to the realization that "the impurities of the animal's body passed off with the milk."
Swill cows were also used for meat at times. When a cow died, the body was discarded into the river or sold to butcher shops in poor neighborhoods - depending on how diseased the animal looked.
The Cows Were Forced To Eat Swill And Live In Their Own Filth
The swill itself was made up of boiling liquid and discarded grain, which was off-putting to the cows until they became so hungry that they at the slop. They ate over 30 gallons of swill per day, producing more milk than their grass-fed counterparts but at a much lower quality. The swill held no nutritional value for the cows, causing their health to fail as well.
In the buildings set up by distilleries, the conditions for the cows were cramped and unclean. They lived in their own filth, covered in bugs, and in ill-health. Many of the cows became so weak from poor nutrition that their teeth or tails fell off, they had sores on their bodies, or they fell over from exhaustion. One account of their conditions described "rows of seven to  across the building, head to head and tail to tail, alternatively." The cows had little or no water, zero fresh air, and were surrounded by an "intolerable stench."