There's a class of antibiotics (ionophores) that are used in cattle feed specifically to manage issues with grain feeding. They reduce incidence of "bloat", and increase feed efficiency. They are also used with other feeds, but the purpose is still to manage digestion issues.

I think there is more use of other antibiotics to treat sickness in feedlots though.

(as an aside, this pdf has an amazing and disturbing illustration of severe bloat on the third page: https://www.animalsciencepublications.org/publications/jas/p... Warning: it shows material ejecting from a medical opening in a rumen.)