Foxtails consist of a group of plants that have sharp spikes which can cause damage to horse's mouths if consumed. Most frequently observed species include:

• Yellow foxtail (Setaria glauca)
• Needle and thread grass (Stipa comata)
• Foxtail barley (Hordeum jubatum)
• Squirreltail (Sitanion hystrix)
• Cheatgrass (Bromus tectorum)

Foxtail plants contain fine, wiry bristles which look similar to a fox's tail. These bristles contain sharp spikelets with have tiny, upwardly directed barbs or points. If eaten by horses, they often can embed themselves in the oral tissues of the horse's mouth. Over time, if the bristles aren't removed from the horse's mouth, ulcers will develop around the bristles. They can appear as discolored areas or a white raised circular area.

Horses are usually at risk of consuming these plants if given low quality hay. Sometimes, horses may start to refuse to eat the hay as a result of pain experienced due to contamination with foxtails. Hay bales should always be inspected prior to feeding to horses, especially if it was cut late. Pastures should also be inspected for foxtails, as horses may ingest in while in the pasture if they have little else to eat.

Foxtails can cause painful blisters and lesions in the mouth, tongue and lips, resulting in the horse's reluctance to eat. Deep ulcerations of the tongue, gums and cheeks may lead to abscesses.