This is how you get a cow to stand still: round up the herd, then urge them into a chute. Some chutes begin as wood, but all end as metal, with what is called a headgate. Today’s chute, in north-central Iowa, is inside a large barn, which protects against the November chill. In single file, the cattle pass through the chute, whose far end faces open doors. As each cow nears daylight and seeming freedom, the farmer pulls a lever to close the headgate, leaving the cow’s head poking out the end of the chute and her body immobilized…