Horses with mild equine asthma hit the treadmill: Here’s what researchers found

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The performance of Standardbreds was still found to be up to scratch, even with less high-intensity exercise. Photo: Historicair GFDL CC BY-SA 3.0
Photo: Historicair GFDL CC BY-SA 3.0

Mild equine asthma was found to have a direct impact on the athletic performance of Standardbred horses assessed in a study in Italy.

Young racehorses can be affected by a mild form of asthma, which can reduce racing performance. Indeed, it shares several similarities with human asthma.

Researchers in the Equine Sports Medicine Laboratory at the University of Milan set out to learn more about the relationship between the increase in inflammatory cells in the bronchoalveolar lavage fluid of horses affected by poor performance through equine asthma and the speed at which the horse’s blood lactate reaches the value of 4 mmol/L — a recognised parameter of athletic capacity.

The study team hypothesized that because mild to moderate equine asthma is a cause of poor performance, the lower airway inflammation could be associated with a reduced lactate threshold.

A bronchoalveolar lavage involves washing a set amount of fluid through a portion of each horse’s lungs and retrieving it for laboratory analysis.

Thirty Standardbreds, with an average age of 3.4, were used in the study. They were among a larger group of Standardbreds referred to the Equine Medicine Unit of the Veterinary Teaching Hospital at the university because of poor performance.

All the horses referred for poor performance had undergone a comprehensive diagnostic investigation. Those enrolled for the study had returned bronchoalveolar lavage fluid results consistent with a mild form of asthma.

The study horses underwent a carefully controlled treadmill test involving increasing speeds, during which blood was taken to measure lactate levels.

A day later, each horse underwent a lavage for analysis.

The results showed a significant relationship between the increase in neutrophils in the lavage fluid and lower speeds achieved when blood lactate levels reached 4 mmol/L.

“This confirms the negative impact of neutrophilic lung inflammation in the presence of equine asthma on athletic capacity and, consequently, on racing performance,” Luca Stucchi and his colleagues reported in the open-access journal Animals.

The results suggest that the accumulation of neutrophils in the airways of mildly asthmatic horses may have a direct impact on athletic capacity, possibly due to impaired alveolar blood-gas exchanges during strenuous exercise, they said.

The researchers, discussing their findings, said poor performance can be the result of a combination of several factors. Indeed, it is common for two or more diseases to be present in the same horse, and the real cause of lower athletic capacity can be debatable.

The reason for the relatively small number of horses used in the study was that the researchers selected only those in which mild to moderate equine asthma was the only disease potentially affecting performance.

“It can be hypothesized that the accumulation of neutrophils in the airways of (asthmatic) horses induces edema and inflammation, which might affect alveolar blood–gas exchanges during strenuous exercise.

“The oxygen transport is consequently reduced, causing a more pronounced exercise-induced hypoxemia, probably leading to a premature passage to the anaerobic metabolism.”

This could induce an early lactate accumulation, resulting in a reduced athletic capacity, they said.

The study team comprised Stucchi, Elena Alberti, Giovanni Stancari, Enrica Zucca, and Francesco Ferrucci, all with the Equine Sports Medicine Laboratory at the University of Milan; and Bianca Conturba, with the Equine Medicine Unit, part of the university’s Veterinary Teaching Hospital.

Stucchi, L.; Alberti, E.; Stancari, G.; Conturba, B.; Zucca, E.; Ferrucci, F. The Relationship between Lung Inflammation and Aerobic Threshold in Standardbred Racehorses with Mild-Moderate Equine Asthma. Animals 2020, 10, 1278.

The study, published under a Creative Commons License, can be read here

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