Respiratory Diseases in Draft Pulling Horses

Who isn’t impressed with the athleticism of high-performance horses—the incredible heights and widths they jump, fantastic speed on dirt and turf, and mind-blowing endurance, sometimes 100 miles in a single outing? Few horse enthusiasts likely conjure images of mighty drafts when they think of equine athletes, yet drafts are exceptionally strong, capable of pulling four times their body weight in competition.

Respiratory diseases often affect high-performance horses, resulting in diminished athletic capacity. These include exercise-induced pulmonary hemorrhage (EIPH), recurrent laryngeal hemiplegia (RLH), and accumulation of mucus in the trachea. Those involved in racing—flat racing, harness racing, steeplechasing—three-day eventing, polo, and barrel racing are often diagnosed with EIPH, or bleeding from the lungs during strenuous exercise, which impedes performance. Likewise, horses with RLH have decreased performance because reduced airflow leads to low oxygen availability throughout the body. Further, moderate to severe tracheal mucus accumulation causes lackluster performances in Thoroughbred racehorses and other sport horses.

When compared to the body of research detailing respiratory disease in light horses, the incidence of the same disease in draft horses has only been superficially investigated. Researchers at the University of Prince Edward Island organized a study to determine the prevalence of respiratory disease in competitive draft pulling horses and to ascertain if respiratory disease is associated with certain risk factors, such as weight, height, age, amount pulled, or competition placing, among this population of horses.

Thirty-four horses were recruited for the study, 24 Belgians and 10 Percherons, all between the ages of three and 20 years old. Most horses were geldings (29), though three mares and two stallions also took part. The weights of the horses varied a great deal, from 1,281 lb (582 kg) to 2,200 lb (1,000 kg). Horses were divided into the three weight classifications used during competition. Maximum weight pulled and cumulative weight pulled were recorded.

Endoscopic examination was performed on all horses an hour after their last pull of the competition. The same veterinarian performed all endoscopic examinations and logged structural or functional abnormalities of the airways as well as any evidence of previous laryngeal surgery. If blood was found, a grade of 1 to 4 was given. A grade of 1 indicated multiple flecks of blood, a grade of 2 for narrow streams of blood, a grade of 3 for multiple, distinct streams of blood covering more than one-third of the tracheal circumference, and a grade of 4 for multiple streams of blood covering more than 90% of the circumference of the trachea. Each horse was also assigned a trachea mucus score from 0 to 4, with a score of 0 indicating no mucus and a score of 4 signifying large, pool-forming quantities.

Of the 34 horses, nine (26%) had an EIPH grade of 1, and none of the horses had a higher EIPH score. Eleven horses (32%) had evidence of RLH, three of which had evidence of “tie-back” surgery, a procedure used to correct RLH. Tracheal mucus was observed in twenty-eight horses (82%): 15 were assigned a tracheal mucus score of 1, 11 a tracheal mucus score of 2, and two horses a tracheal mucus score of 3.

Despite observation of respiratory disease among competitive draft pulling horses, no risk factors were identified.

Omega-3 fatty acids, with their ability to reduce airway inflammation, have been hypothesized to decrease the incidence of EIPH. Further, diets rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) may also enhance erythrocyte membrane fluidity during exercise and improve pulmonary hemodynamics, thus reducing EIPH.^** A study at Kansas State University showed that 10 Thoroughbred horses fed a DHA- and EPA-enriched diet for 83 and 145 days had decreased EIPH.⁺

Choose EO-3, a long-chain polyunsaturated omega-3 fatty acid supplement, as it is a marine-derived oil that is a direct source of DHA and EPA. Plant-based omega-3 supplements, like flax products, provide horses with alpha-linolenic acid that must be converted to DHA and EPA. Studies have shown that this conversion is inefficient in horses, so marine-derived EO-3 is the best choice.

^*Burns, J.J., K.M. MacMillan, and E. John. 2023. Prevalence of exercise-induced pulmonary hemorrhage, tracheal mucus and recurrent laryngeal neuropathy in competitive draft pulling horses. Journal of Equine Veterinary Science:104895.

 ^**Portier, K., B. de Moffarts, N. Fellman, et al. 2006. The effects of dietary N-3 and antioxidant supplementation on erythrocyte membrane fatty acid composition and fluidity in exercising horses. Equine Veterinary Journal (36):279–284.

 ⁺Erickson, H.H., T.S. Epp, and D.C. Poole. 2007. A review of alternative therapies for EIPH. In: Proceedings of the American Association of Equine Practitioners 53:68-71.