Any source on the feed being the factor necessitating the antibiotics? Afaik, there just are way too many and they tend to stand in their own shit all day and that makes the antibiotics necessary.

(Somewhat related: I was a bit horrified recently when my dad told me about growing up on a farm and how badly their cattle took suddenly switching from their winter feed [siloed grass] to their summer feed [fresh grass]. When they would become overly gassy after the switch, his granddad would routinely pierce their rumen to let the gas out, along with a bit of blood. This procedure turned out to be completely unnecessary when they started mixing the feed for a few weeks in spring.)