Milk is mixed with other cows prior to homogenization to average out the taste, and prevent one cancerous ruptured-cyst "**pus bag**" cow from being the primary contributor to a gallon of milk. It also hides the sad effect of a sick cow mainly only producing a lot of pus when milked. Staph infected pus-rudders can be systemic to a portion of a heard though. I was talking above about a ruptured tumor or cyst being vacuum milked out. **The average cup of milk in the United States will only contain about a single drop of pus.** Some batches, far far far more pus. **How much pus is there in milk?**: https://nutritionfacts.org/2011/09/08/how-much-pus-is-there-in-milk/ > When a cow is infected, greater than 90% of the somatic cells in her milk are neutrophils, the inflammatory immune cells that form pus. The average somatic cell count in U.S. milk per spoonful is 1,120,000. Basically, once a cow becomes a "pus bagger" it goes unnoticed for several days.