Cover Story | Dentistry

Omega-3 Supplements Appear to Combat Dust Exposure in Healthy Racehorses

By Paul Basilio

Inflammatory airway disease is a common condition among young racehorses that can significantly affect performance and quality of life, and prior research has shown that as a horse’s exposure to dust increases, so does the proportion of neutrophils found on bronchoalveolar lavage (BAL).

After his own research showed that omega-3 supplementation with docosahexaenoic acid (DHA) sped up symptomatic resolution in severely asthmatic horses (heaves) fed a low-dust diet, Laurent Couëtil, DVM, PhD, DACVIM, the director of Equine Research Programs at Purdue University, and his colleagues conducted a new study to determine whether omega-3 supplementation would be effective without dust mitigation.

“Our hypothesis was that racehorses fed the traditional hay-grain diet supplemented with fish oil, which is rich in omega-3 fatty acids, for 4 weeks would have a decrease in the BAL neutrophil proportion compared with racehorses fed a placebo,” Dr. Couëtil said at the 2024 ACVIM Forum in Minneapolis.

The double-blind, controlled trial had a randomized block design and took place at 4 racetracks across the United States. They included 20 racehorses at each of the tracks in California, New Mexico, Indiana and Florida; 2 of the tracks—1 each in California and Florida—were in an urban setting, and 2—1 each in Indiana and new Mexico—were in a rural setting. Horses were at the racetrack for at least 6 weeks prior and have no abnormal bloodwork or signs of systemic illness.

Each group of 20 horses ate their regular diet and were randomly assigned to receive a 50-mL dose of either fish oil, which has high levels of omega-3 fatty acids, or corn oil, which is low in omega-3 and high in omega-6 fatty acids. Horses underwent a physical examination, blood collection and BAL. Dust exposure in the horse’s breathing zone was measured through a wearable dust sensor that was created for this purpose at baseline and at 4 weeks.

“We measured particulate matter of less than 2.5 µm and 10 µm [PM2.5 and PM10] at the level of the horse’s nose,” Dr. Couëtil said. “The devices were also equipped with a video camera pointing at the nose, so as we measured dust exposure, we could see what the horse was doing in real time.”

Plasma omega-3 concentrations were assayed, and BAL was collected at baseline and at 4 weeks. Using a generalized linear model, the effects of supplementation and PM exposure on BAL neutrophil proportions were measured, with statistical significance set at P<0.05. A total of 78 horses completed the 4-week trial.

There were no differences in the particulate matter exposure among the groups, but there were significant differences among racetracks—horses in California and Indiana were exposed to higher levels of PM2.5 and PM10 than those in New Mexico and Florida.

Results of BAL cytology showed that the horses in Indiana and New Mexico tracks had significantly higher proportions of neutrophils, the horses at the Indiana track had significantly lower proportions of mast cells, and the horses kept in New Mexico had significantly higher proportions of eosinophils. Significant differences were also found in the fatty acid levels, as the horses in California tended to have a higher ratio of omega-3s to omega-6s than the horses in Indiana. There were no other significant differences among locations, and there were no changes in the proportions of eosinophils or mast cells during the study.

Overall, the horses fed the fish oil supplement for 4 weeks had a significant reduction in neutrophil proportions when compared with the corn oil group.

“The horses fed the fish oil were within normal limits after the 4 weeks, but there was no change over time in the horses fed the corn oil,” Dr. Couëtil explained. “When we looked at the relationship between BAL cytology and dust exposure, we found an increase in BAL neutrophils as the exposure to dust increased in the placebo group, but there was no change in the fish oil group. The omega-3 supplement completely abrogated the response to dust particles.”

Dr. Couëtil is a consultant with Boehringer Ingelheim Vetmedica and is the manager of Equine Lung Experts LLC. MeV