If a cow rarely gets an infection, yes they’ll use antibiotics, just like an ear infection for human kids, UTI for adults, etc. The other option can be fatal for the cow. However, the cow is separated and milked with her own single machine and it is dumped entirely. Then she must wait many weeks after being off the medication with continued testing to go back to the main parlor. They milk gets tested on every single load. Any trace of antibiotic would shut down the farm so they absolutely abide by this.