I've looked around and I can't see any requirement to scan for microchips at slaughter.
I don't know anyone that has done it with horses... But I can't see why the same tech wouldn't be as good in horses as it is in dogs. Is it becoming more common?
Maybe it was just wishful thinking on my part coz I didn't see any reason why it wouldn't work for horses as well as it works for dogs and cats at the shelter either, as long as they scan for them first. It sure would be nice coz nobody would know the chip was there so there would be no attempts to alter or camouflage it.