The more dense the animal population, the more likely disease will be present, say veterinarians Mike Apley and Mark Hilton. Simple phrases like “exposure equals disease” or “the solution to pollution is dilution” are accurate, they say.

As an example, why does one Midwest operation calving in a mud lot in February have calf diarrhea while a herd just a mile down the road that begins calving in late April on pasture has none?

A scouring calf produces billions of disease organisms. If there are 40 pairs on five acres, it's almost a guarantee that more calves will be exposed and they will amplify that pathogen. Billions of organisms turn into hundreds of billions.

All neonates are “incubators of disease.” They simply do not possess the level of immunity that an older animal possesses. If this same group of 40 cows calved on 80 acres of pasture, the chances of calf scours developing in the herd are many times less likely.