Get a hold of your local vet. Bet they need a round of antibiotics for BRD/shipping fever. It’s a respiratory virus that was probably picked up in the sale barn.
When I buy from a sale barn I stop at the vet on the way home and they get a shot that evening or the next morning. Then they are monitored and quarantined for 10-14 days. Resflor is what my local vet usually prescribes. Follow the label and residue will be out of their system in a few weeks. Well before slaughter or resale.
Weigh their feed. Shoot for 1-2% of body weight. Buying a feed from a Local mill that has a known protein and fat content is what I would recommend. Also get something with a vitamin pack and offer a mineral/salt supplement either mixed with feed or free choice. I like commodity feeds not pelleted. Cheaper and seem to eat it better. TSC is too expensive to feed calves on. Their feed conversions aren’t good enough for that gold.