Foxtail (Setaria spp.) stomatitis in a horse
Murray Hazlett, Kathleen Taylor, Bruce Watt
A 20-y-old warmblood gelding was examined in December for a recently appearing 1 x 3 cm area of ulceration and granulation tissue formation on the upper lip (Fig. 1A). The lesion bled when irritated. It was managed with topical steroids for a month then re-examined. The lesion had grown to 2 x 8 cm. Three biopsies were taken and revealed severe ulceration with pyogranulomatous inflammation and large amounts of foreign-body plant material (Figs. 1C, 1D). The material was similar to that published on foxtail (Setaria geniculata) stomatitis, with reports of outbreaks in stables of 2 horses1 and 25 horses.2 In our case, only one horse was affected, although it was noted that 2 other horses on the farm had feed material stuck in their gums and lips – these horses were not biopsied as removal of the feed material was uneventful. No more cases were noted, although the hay was not changed. The hay was not examined for foxtail, but was simple grass hay with no clover or alfalfa and no obvious weeds.
The horse was treated by rubbing the area with dry gauze squares The lesion fully resolved when rechecked in late March.
Although we cannot be certain this was Setaria geniculata, the foreign bodies seen are most likely some type of foxtail. The awns of this grass have microscopic barbs on them causing the plant material to lodge in tissue (Fig. 1D). In the 2 published cases referred to, the grass was identified as prairie foxtail, and examination of hay identified numerous foxtail seed heads (Fig. 1B).
A search of the AHL case archives since 2007 did reveal another case in a 6-mo-old foal that had a “mass growing and spreading over incisors”. AHL
1. Johnson PF, et al. Ulcerative glossitis and gingivitis associated with foxtail grass awn irritation in two horses. Equine Vet Educ 2012;24:182-186.
2. Turnquist SE, et al. Foxtail-induced ulcerative stomatitis outbreak in a Missouri stable. J Vet Diagn Invest 2001;13:238–240.
Figure 1. A. Lesion on the upper lip (arrow). B. Appearance of foxtail seed heads in mixed alfalfa-grass hay (from reference 2, reprinted with permission, courtesy of Dr PF Johnson and Equine Vet Educ). C. Low-power H&E of the biopsy, showing large number of awns in the inflamed lesion (arrows). D. Close-up of an awn, showing the sharp barbs (arrows).