I have used Excede to treat respiratory infections in 200 lb. calves, a snake bite, skin infection (calf had ringworm, rubbed around the eyes, got it all nasty and infected). It worked for these issues and I didn't have to re-treat. It is expensive but what isn't these days. The bottle has to be used within 3 months of opening, so it says, so once you open it if you aren't using it when you bring calves in from the sale or something you had better get to using it, LOL. I had a cow retain a placenta recently from a premie calf and so I gave her shot of it since the bottle is just about to "expire."
I like the behind the ear application alot. IT is very easy to do.