That's tough -- since anything in the right amount can be a problem. At the Animal Poison Control Center, chocolate is the number one holiday hazard we see.
I would also say gums, mints, and other candies sweetened with xylitol since it doesn't take very much to cause problems.
It is insane to say that the round-ups are not working if you yourself have seen that the horses are healthy and happy out there. That is the point of the roundups. A mare can have one foal per year and each foal can begin having a foal per year at…