Indeed I have heard of Staph aureus mastitis which is spread by milker’s hands that contaminate the udder and the milking units. It is not part of bovine normal flora.
Good grief, are you trying to be obtuse? SA mastitis is just one good example of the prevalence of Staphylococcus aureus in cattle. There are more.
Who gives a rats behind how it was introduced or whether “it’s part of bovine normal flora”. SA in cattle is not “a rarity” as you proclaim. SA IS contagious meaning it can transfer from on animal to another. Once it is introduced it can proliferate without human intervention. If it exists at all in a given animal and that animal is overtreated with antibiotics for whatever affliction then there a more than fair chance that a resistant variety will emerge.