Technically you can use horse ivermectin for rabbits. However, it is very difficult to dose. The horse paste is very concentrated--you need a tiny drop for a rabbit dose. The horse stuff is also not evenly distributed in the tube, so if you give a small blob, it may contain more or less of the active ingredient. It is easier to get the injectible form for farm animals and dilute it properly to give the right dose orally. The injectible liquid is much easier to dilute because it is not a gel like the horse stuff. It is still given orally, however.
This site can give you the right dose for a rabbit:
http://homepage.mac.com/mattocks/morfz/rx/drugcalc.html
I have given the horse stuff to bunnies and greatly regretted it. My Dutch had a hypersensitivity to it and nearly died. The fact that it was a much higher dose than needed made the reaction even worse. On the other hand, my Holland lop got the same dose, without a hypersensitivity, and had no problems. Now I will not give ivermectin unless under the direct supervision (and watching for 2-4 hours post-dosing) of a vet. It is also important to note that Dutch, vienna, and blue-eyed bunnies seem to have a genetic tendency to hypersensitivity, somewhat like collie dogs do. Bad reactions like my Dutch had can occur in any breed of rabbit, but they are more common in bunnies that carry these genes, it seems.
I personally would go for Revolution instead of ivermectin first because it is safer. I would only give ivermectin if Revolution had been unsuccessful, and then, only under the direct supervision of a vet, because if a bad reaction happens, it is very serious for the life of the rabbit. I honestly didn't think Tony would make it, and neither did the emergency vet. He was there for several days and we even did an experimental last-resource treatment. It was an experience I hope nobody has to go through, and from a practical point, the cost of getting Revolution for my two bunnies would have been at least 10x less.
