While mature cows will build immunity to internal parasites, calves take a different approach. As they graze, they’ll pick up larvae, and their immune systems aren’t yet equipped to deal with the challenge. So, even in a “normal” year, and especially in a dry year when nutritional stress is a concern, worming calves can pay.

So can worming stocker cattle. “And I don’t have a problem with giving a full therapeutic dose of each (type of wormer – an avermectin and a ‘white’ wormer) to the animal at the same time. As long as the two drugs are in different families, you’re not going to increase the toxicity to the calf, but you may increase the toxicity to the worm,” Craig says.

He only recommends this for cattle headed for a feedyard. Stockers aren’t going to stay on the pasture permanently and any internal parasites that survive and possibly build resistance will move on with the calves when they get a feedyard address. “I wouldn’t do that with a bunch of older cows,” he stresses.

However, he thinks worming any new arrivals, not just stockers, is a sound strategy.

“The one place I might be concerned is if you brought in cattle from another place; they could bring things with them. And some of these may not be desirable to have as your own,” Craig says.