Horses with problems involving their mouths often have bad breath or a foul odor emanating from their head. Wounds in the mouth, periodontal disease and feed pockets, loose teeth, abscessed teeth, and ulcers in the cheek from dental overgrowth or retained caps all can result in a variety of pungent and unpleasant odors. Horses with certain types of abscesses in the throat or rear of the mouth can have a bad odor around their mouths.

Sour breath and sour mouth can be associated with intestinal obstructions that may cause signs of abdominal pain (colic). The odor is due to the buildup of excretory products that normally pass out through the equine digestive tract. The same applies to horses experiencing kidney failure. In that case, buildup of toxins normally excreted in the urine causes an odor that can be detected in the breath and around the mouth.