Agribuzz with David Leyonhjelm
May I remind commenters that David is a veterinarian. I'm no vet but do see every day how chickens in large flocks behave and it's not always so clear cut. For instance, a sick hen in a battery system is quickly and easily noticed while a hen that is sick in a "free range" environment often disappears without a trace after being completely devoured by the others. This poses a quarantine risk where it's easier for the whole flock to be wiped out via a virile pathogen.
Believe it or not, farmers actually know more about their animals or crops than armchair commenters.