Withing a few days after being born. Usually they won't touch it early on but keep it out for them and when they get curious they will start nibbling. Sometimes I will put a little in my hand and put it in their mouth when they try to suck your fingers. Gives them a taste. I use a textured feed with rolled corn, oats, and barley in it. Research has shown that consumption is the highest on a textured feed and the goal is to get the calves to eat as much starter as possible as soon as possible. I won't use a starter that is less than 18% protein either.