We have a full laboratory for rapid diagnostic information, and a quarantine barn that allows us to safely care for horses with potentially infectious disease. We use this mostly for colitis (diarrhea) cases.
No, having a horse here is not the same as a mobile vet hanging a couple of IV bags in your barn!
When a horse is in our hospital, we perform the diagnostic tests necessary to make a correct diagnosis, and the ongoing monitoring to make good clinical treatment decisions. Sick horses here are constantly monitored and their treatment adjusted accordingly.
Yes, it is more expensive, but this is what gives the horse the best chance of survival.