Q. I have a 15-year-old mare that regurgitates her grain. My vet and longtime horse friends have no idea the reason why she does this. It seems as if this could be dangerous to her throat and is very messy. Also, I notice she will also do this when in her stall and bored. I’ve had her vet checked and her teeth floated, and she has no problem with grass or hay.

—Vickie Bryan Wright, via Facebook

A. This is certainly an unusual case, so I’ll go through it step-by-step.

First, the use of the term regurgitation is important. In small animals like dogs, an initial decision between regurgitation and vomiting would have to be made, but since horses are unable to vomit, it is the former. Regurgitation is essentially passive flow of ingested food in the wrong direction, and it localizes the problem to the esophagus (the same site as choke). In your horse’s case, a possible cause of regurgitation is that the esophageal wall is not working correctly, although a physical problem with the esophagus is also possible