This past week, I had three clients notice that their horses were becoming difficult to bridle, and on closer inspection found that the horses lips were raw and irritated, the gums were red and inflamed, and there were several large lesions on the inside of the front lips. We were all stumped what was causing the irritation, but the vet was very familiar with it and informed the owners that it has been somewhat common in our area, Southeast PA.
The culprit? Microscopic barbs found in foxtails in the hay. The vet spent over an hour picking these barbs from the gums of the first horse. I was very curious about this since I had never seen it before and these horses were at two separate farms. I did some research online and found that the foxtails are a concern from mid to late summer through the fall. The barbs are located on the seed head or stem and do provide physical trauma to the mouth and gastrointestinal track. They are a problem whether grazed or in hay. The best way to avoid these seems to be through good pasture management, mowing before the seed heads fully develop and keeping them knocked down. When buying hay, it is important to check for foxtails and ask when the hay was cut and baled.
I found this information at the MSU Extension page, http://msue.anr.msu.edu/news/mouth_blisters_in_horses. Image is courtesy of www.forestryimages.org.
Additional information can also be found at http://www1.extension.umn.edu/agriculture/horse/pasture/mouth-blisters/docs/mouth-blisters.pdf