Higher hematocrit levels seen in horses affected by lung bleeding

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Study in Italy looked at treadmill test results and blood parameters in a group of Standardbred racehorses.
Photo by sniggie

Bleeding in the lungs of Standardbred racehorses appears to be unrelated to the aerobic and anaerobic capacity of the affected animals, researchers report.

The condition, formally known as exercise-induced pulmonary hemorrhage (EIPH), is common among racehorses worldwide. It affects from 43% to 75% of racehorses when diagnosed on a single examination, and up to 95% in the case of repeated examinations.

Its diagnosis is based on the detection of blood in the trachea after strenuous exercise, or the presence of red blood cells in lavage fluid washed from the lungs.

Although EIPH is commonly associated with poor performance, scientific evidence supporting this observation is low.

Researchers with the University of Milan in Italy set out to explore associations between EIPH and fitness parameters in Standardbreds during a treadmill test.

The clinical records from Standardbreds referred to the Equine Medicine Unit of the Veterinary Teaching Hospital at the university for poor performance evaluation between 2002 and 2020 were reviewed.

All horses were in full training and underwent a complete diagnostic protocol. This included the collection of their history, a clinical physical examination, laboratory blood analysis, a lameness evaluation, electrocardiogram, thoracic ultrasonography, endoscopic investigations of their airways, and a high-speed treadmill metabolic test. A lung lavage and analysis was also conducted after the treadmill test.

Horses showing signs of systemic illness, lameness, heart problems, upper-airway obstructions or muscle problems were excluded from the study since these could influence athletic performance.

In all, key parameters from 81 horses were included in the study. Twenty-six of the horses showed no evidence of EIPH during a tracheoscopy (32.1%), while the remaining 55 (67.9%) were EIPH-positive.

On the treadmill, the speed of each horse when their heart rate hit 200 beats per minute, and their speed and heart rate when their blood lactate concentration reaches 4 mmol per litre, are considered good fitness indicators.

The researchers, writing in the journal Animals, reported finding no relationship between EIPH and these three key fitness parameters.

The blood work turned up an interesting result. The EIPH-positive horses showed higher hematocrit values. A hematocrit test measures the proportion of oxygen-carrying red blood cells in the blood. It is also called a packed-cell volume (PCV) test.

The higher hematocrit levels in EIPH-affected horses suggest the possible influence of higher blood concentrations on the increase of pulmonary capillary pressure as a part of the cause of EIPH, they said.

However, as hematocrit variations during exercise are affected by different factors, such as the blood reserves held in the spleen and intercompartmental fluid shifts, further studies are needed to investigate its possible role in EIPH, they said.

“Although our study found no association between EIPH and the main treadmill parameters, the causative role of EIPH in poor racing performance cannot be excluded,” they said, “as it may be related to different mechanisms.”

The authors noted that all horses in the study showed lung lavage profiles typical of mild to moderate equine asthma.

“This,” they said, “could be due to the fact that the population included in the study consisted mainly of young racehorses in training, among which mild to moderate equine asthma can have a prevalence higher than 80%.”

The authors stressed that their findings do not rule out the potential role of EIPH in decreased racing performance, which should be further investigated.

The study team comprised Chiara Lo Feudo, Luca Stucchi, Giovanni Stancari, Elena Alberti, Bianca Conturba, Enrica Zucca and Francesco Ferrucci, all with the University of Milan.

Lo Feudo, C.M.; Stucchi, L.; Stancari, G.; Alberti, E.; Conturba, B.; Zucca, E.; Ferrucci, F. Associations between Exercise-Induced Pulmonary Hemorrhage (EIPH) and Fitness Parameters Measured by Incremental Treadmill Test in Standardbred Racehorses. Animals 2022, 12, 449. https://doi.org/10.3390/ani12040449

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

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