The use of antibiotics in rearing preweaned calves has changed considerably in recent decades. Many operations are relying less on antibiotics today to keep their calves healthy. Some of that reduction has been due to regulation, and some by intentional management strategy.

When calf milk replacer became commercially available decades ago, adding antibiotics like oxytetracycline, neomycin, and chlortetracycline was a common practice. Often these were delivered at “sub-therapeutic” levels, meaning they were not intended to treat disease, but rather to promote growth.