Oesophageal Obstruction, or “choke” refers to an obstruction in the oesophagus (the tube that carries food from the mouth to the stomach), unlike in humans where choking refers to an obstruction in the trachea (windpipe). The most common symptom an owner will see is feed material coming out of the nostrils, but they might also notice choking horses struggling to breathe, coughing, not eating and demonstrating Colic like behaviour as they are uncomfortable. Choke can very quickly be fatal so rapid veterinary treatment is required to give the horse the best chance of survival.
Horses are grazing animals and can often eat food too quickly, particularly if they are offered a tasty treat, but it can also occur from hay, hard feed, or non edible objects. Choke often occurs when horses eat their food too fast without chewing it properly. This means that the food can be too hard as hasn't been softened by saliva and can form a solid mass that can then become lodged in the oesophagus.
Some horses and ponies are pre-disposed to choke due to poor anatomy or underlying health conditions.
You can find out more information about Choke here