This sounds like an "Internet of things" opportunity: an implant that monitors an animal's temperature, antibody levels etc. Then they could target only the animals with telltale symptoms.
The reader and the software are going to be a few hundred dollars or maybe a couple thousand. But it's a one time investment, plus ongoing implants as the herd changes over time.
I suspect the main selling point is going to be the one-time capital investment aspects and the fact that antibiotics are being painted as an undesirable additive in meat and dairy. When the general public starts to dislike a substance, suppliers scramble to distinguish their products, e.g. "No added growth hormones" and the like.