I think it's really important for horse owners and horse lovers to learn about choking.
The first thing to learn about choking is the symptoms. Believe it or not, the symptoms of a horse choking are much different from the symptoms of a human choking. One of the first things you'll notice if your horse is choking is that they are very distressed. There will be a lot of saliva coming out of their nose and they'll be drooling too. Your horse probably won't be able to eat or drink, and you might be able to see some swelling on the left side of their neck.
Next, you should learn the cause of choking. Usually it is a large piece of apple or carrot (or any other food/treat for that matter), but it can also be swelling of any kind in the esophagus. Anyway, this is a case where I would call the vet.
The treatment for choking could be to gently massage any swelling on the neck to help the stuck food pass on. I would definitely call the vet in this situation. The vet might have to use a stomach tube to get the excess saliva out.
I hope this will help you if you encounter this situation. Just remember that the best way to prevent choking is to prepare your horse's food properly!