I've just had a phone call from my nephew who is a senior customs officer at Heathrow Airport, London. They have been alerted about drugs being inserted into horse's rectums and taken across borders, and they had a lead from the US. Apparently, the horses are starved for a couple of days to empty the rectum, then the package is sewn into the rectum for transport.
I've never heard of this, but maybe some one else has, in which case I would be glad of any information to pass on. It seems that there's no limit to what drug smugglers will do. I had heard of it with dogs. It's really disgusting.