The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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34 TheHorse.com THE HORSE October 2015 "Trichothecenes have radiomimetic properties (like radiation toxicity) and generally target bone marrow cell precur- sors, with T-2 being the most toxic— actually, one of the most potent toxins known," Liepman said. "The (bone marrow suppression) in these cases was consistent with trichothe- cene intoxication, which is poorly docu- mented both in horses and from a forage source," Liepman said. "Reports typically mention these toxins in association with cereal grains. Most toxicologists didn't believe me when I said this was a forage contamination—that's how rare it is!" And although not all horses recover from severe disease, these cases suggest that recovery is possible following severe myelosuppression due to trichothecene intoxication in horses, she noted. Help prevent your horses from ingest- ing trichothecene by ensuring the hay and grain you buy are produced properly. Heaves and Tracheal Microbiomes: Is There a Connection? Long-established potential triggers for recurrent airway obstruction (RAO or heaves) range from an unclean environ- ment and lack of fresh air to dusty bed- ding and moldy hay. But could we soon add microbiomes to that list? A microbiome is, basically, the collec- tion of microbial "communities" living on or in different sites of an organism's body. Scientists believe microbiomes in the airways could play a role in chronic inflammatory disease development there, so Julia Montgomery, DVM, PhD, Dipl. ACVIM, an assistant professor of large animal medicine at the University of Sas- katchewan's Western College of Veterinary Medicine, and colleagues studied whether microbiomes play a role in recurrent airway obstruction, as well. The team evaluated the tracheal microbiomes of three healthy horses and five with heaves on two occasions, about two weeks apart. They collected tracheal aspirates and examined the DNA in those samples. Specifically, the team estimated the samples' total bacterial load using quantitative polymerase chain reaction testing, which scans for bacterial DNA; then they organized the DNA sequences they found into operational taxonomic units (OTUs). Essentially, researchers use OTUs to classify microbial communities at the phylum level (recall from biology class that units of classification, from largest to smallest, are kingdom, phylum, class, order, family, genus, and species) and to identify "nearest neighbors" based on known sequences at the species level. After analyzing 15 samples, Montgom- ery and colleagues determined that: ■ Total bacterial load was higher in horses with heaves than in healthy horses; however, there was considerable variation among the group members between the first and second samplings; ■ The microbiomes from heaves horses appeared to have a greater species rich- ness (a larger variety of species in the sample) than healthy horses; and ■ Despite that, the microbiomes didn't appear to differ statistically between groups at the phylum level. ■ Repeated evaluations showed microbi- ome profiles remaining similar in six of the eight horses throughout the study. "This pilot study suggests horses with heaves may have a higher bacterial load with greater species richness, but their microbiome profiles are not distinguish- able from those of healthy horses at the phylum and OTU level," Montgomery said. The team said these findings could help heaves researchers and veterinarians: ■ Investigate the association between the microbiome and inflammation in RAO horses, which could contribute to better understanding RAO's mechanisms; ■ Study antibiotic use in affected horses and evaluate its effect on microbiome changes and clinical response (how patients respond to treatment); ■ Conduct studies to determine whether differences in the microbiome are pres- ent in young horses and use those to predict disease development; and ■ Examine probiotics' effects on the air- way microbiome. This could reveal that we can manipulate airway microbiota, which might influence disease suscepti- bility and development. The team added that further work is underway to confirm their initial findings in a larger group of horses. Upper Eyelids Have the Upper Hand in Subpalpebral Lavage Study Veterinarians got it right in the 1990s, when they developed an alternative to toppled stepstools, dropped ointment tubes, and the reduced compliance that can come with medicating horses' eyes for days or weeks on end. A subpalpebral lavage (SPL) allowed them to administer drugs to the surface of a horse's eye with ACVIMForum Horses with heaves might have a higher bacterial load with more species richness than healthy horses. COURTESY CHRISTINA WEESE/PORTRAITSOFSASKATOON.COM Spend a little money on (subpalpebral lavage) catheters early on, rather than waiting to put them in when horses have become difficult." DR. GAYLE HALLOWELL