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A Tale of Foxtails—Setaria genus and its effect on equine husbandry

Foxtails are all members of the Setaria genus, with the two most common species in Indiana being Setaria viridis (green bristle grass) and Setaria pumila (pidgeon grass). Their construction includes a grassy stem and a seed dispersing aid known as a diaspore whose appearance resembles a fox’s tail (Figure 1.1). This diaspore is made up of small barbs that are easily dispersed and cling well to animal fur as they are designed for unidirectional movement. Once a barb is caught it is very difficult to remove due to retrose barbs and instead continues to burrow into fur or skin with continued motion thereby causing a variety of trouble to its carrier.

Figure 1.1: Left to right, dried Setaria viridis on the and Setaria pumila. The plume of|
 the seed head is what gives the foxtail its common name

In the equine world, foxtails are most worrisome when they are present in hay or pasture. Foxtail appears to be most proliferative during times of drought due to its biology making it more accepting of high temperature and prolonged sun exposure; it is also at this time that lower quality and possibly foxtail contaminated hay is likely to be fed because of a lack of better hay options. It is also suspected that with the continued climate change and increased global temperatures, presence of foxtail will only increase. Horses can consume the stem of the foxtail without adverse effect, however when the seed head, or diaspore is eaten the barbs quickly detach from each other and become lodged in the gum line, lips, and oral mucosa. Continued eating of foxtail contaminated hay or pasture leads to irritation and signs such as excessive salivation in mild cases to difficulty chewing and mouth odor. In severe cases it can lead to anorexia due to inflammation and ulceration on the gums, tongue, and interior and exterior lips

Once foxtail is found, treatment will depend on if the horse is displaying signs of mouth pain or discomfort. The first step in any foxtail treatment is removal of the source: pasture, hay, or riding location, if the horse is not displaying signs of discomfort, this may be enough. Once foxtail barbs have become lodged in the gums, lips, and tongue they are very difficult to remove, but with time the barbs will work themselves out. A recent study documented that following removal of the foxtail, horses with associated oral ulcers spontaneously resolved within 10 days. This is not the case for the pictured horse, but 7 days following the removal of foxtail and flushing of her mouth, her ulcers and gums appear much less enflamed and are beginning to heal. In the case of a horse with severe ulcerations a diluted chlorohexidine rinse of the affected area combined with mechanical removal of the barbs with gauze and hemostats may be appropriate. While the barbs will work themselves out, a horse with severe mucosal irritation will benefit from a sedated de-bulking and flushing of the ulcers, allowing the affected tissue to begin healing more rapidly.

Figure 2.1: Above are two different presentations of foxtail in hay. The diaspore
plumage makes foxtail readily identifiable.

Foxtail consumption is a very real problem that affects the equine community, and it is important to remember that not all horses consuming foxtails will be affected in the same way. Just as with bee stings or drug reactions, all horses respond uniquely to the foxtail they ingest. Some can consume foxtails with no repercussions while their pasture-mate or stall neighbor consuming the same grass or hay may have severe ulcerations or mucosal irritation. It is important to remember to vigilantly monitor roughage for foxtail presence and be prepared to treat affected animals if foxtail is fed, whether intentionally or accidentally.

Written by Taylor Huffman DVM

Douglas, B.J., Thomas, A.G., Morrison, I.N., Maw, M.G., 1985. The biology of Canadian weeds: 70. Setaria viridis (L.) Beauv. Can. J. Plant Sci. 65 (3), 669–690.

Kutasi, O., Andrasofszky, E., Szenci, O., Bersenyi, A., Siller, I., Abonyi, T, 2018. Foxtail grass
(Setaria viridis)-induced ulcerative stomatitis-gingivitis resembling viral vesicular stomatitis in horses. Livestock Science. 215 (2018) 41-45.

“Setaria.” Indiana Plant Atlas, 28 August. 2018, Accessed 2 November 2018.

Figure 1.1

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Figure 2.1 L picture:
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