Why Do Racehorses Get Nosebleeds?

Nosebleeds in racehorses, while concerning, are a well-documented and carefully managed part of the equine welfare initiatives within the racing industry.
Published
11th Feb 2024
Reading time
6 mins
Exercise Induced Pulmonary Haemorrhage (EIPH) is a condition where racehorses, often called 'bleeders,' experience visible nosebleeds known as epistaxis when exercising. The racing industry has strict measures to manage and mitigate the effects of EIPH, which can result in a horse being barred from racing under HISA rules.

The awe-inspiring spectacle of a racehorse at full gallop is a sight to behold. Their powerful lungs, large heart, and a spleen capable of releasing millions of stored red blood cells into the bloodstream during intense exercise make them the super athletes of the animal kingdom. However, there is a phenomenon that often sparks concern among spectators: a racehorse with blood in its nostrils. A better understanding of this can provide valuable insight into the welfare and performance of these majestic animals.

‘Bleeding’: EIPH versus Epistaxis

The key to appreciating why racehorses sometimes get nosebleeds lies in recognizing a condition known as Exercise Induced Pulmonary Hemorrhage (EIPH).  Horses that experience EIPH are sometimes colloquially called ‘bleeders’. As the name suggests, this particular condition is initiated by exercise, and is not unique to horses but is experienced by human athletes as well.

The technical term “epistaxis” is applied when blood is visible at the nostrils.

Racehorses, in particular, exhibit an extraordinary heart size as a percentage of their body weight compared to other equine breeds and mammals. A Thoroughbred racehorse’s heart typically accounts for up to 1% of their body weight, while in humans it is around 0.55%.

A horse’s mean arterial blood pressure naturally increases almost five times during exercise, due to their large cardiac output.

Consequently, it is not surprising that a horse’s mean arterial blood pressure naturally increases almost five times during exercise; from 20mmHg to over 90mmHg, due to their large cardiac output.  Intense exercise also floods the bloodstream with additional red blood cells, notably increasing the viscosity (thickness) of the blood. The pressure inside the smallest blood vessels – the pulmonary capillaries – intensifies. In about 75% of horses, this results in some degree of EIPH due to stress failure of these capillaries.

When we inhale, our diaphragm muscle creates a negative pressure in our lungs, drawing air in.  In resting horses, the negative pressure is approximately -5.3mmHg, but during exercise, it ramps up to a staggering -64mmHg.  When a racehorse gallops, its breathing rate can surge from approximately 80 liters of air per minute to a remarkable 1800 liters. 

Despite horses having stronger alveolar and pulmonary capillary walls compared to other species, these significant changes in air and blood pressure can cause blood leakage from broken blood vessels. The leaked blood is then transported up the trachea from the lungs. In a small percentage of cases (about 0.15% of starters), the bleeding is enough to enter the nasal passages and the nostril(s), giving the appearance of a nosebleed (epistaxis).

This is an important distinction since it is this small group of horses that are subject to rulings under the Horseracing Integrity and Safety Authority (HISA) Anti-Doping & Medication Control and Safety Programs.

The Impact of EIPH on Racehorses

EIPH can have a deleterious effect on the performance of a racehorse.  Horses experiencing epistaxis will be placed on the Veterinarians’ List and repeated episodes can result in a horse being barred from racing under HISA rules.

Horses generally recover well from a ‘bleeding’ episode and can easily transition to other less intense activities when they are retired from racing.

The strict rules around racehorses that experience epistaxis are important.  Industry participants are motivated to prevent any degree of EIPH where possible as it may affect a horses’ welfare.  Studies have shown that horses suffering from EIPH tend to exhibit decreased performance compared to non-bleeding horses.  Horses generally recover well from a ‘bleeding’ episode and can easily transition to other less intense activities when they are retired from racing.

Salix®, also known as ‘Lasix®’, are brand names for the drug furosemide. The use of furosemide in racehorses is controversial. Furosemide is permitted during workouts and may be administered for racing, within certain rule frameworks. While it is believed that it may reduce the severity of bleeding associated with EIPH, there is also concern that it may be performance enhancing. Regulatory entities are evaluating the use of furosemide administered on race day. 

The Horseracing Integrity & Safety Act has mandated and is funding research into the appropriate use of furosemide as a race day medication. Currently under the HISA Anti-Doping & Medication Control and Safety Programs, the ban on furosemide applies to 2-year-old races and stakes races.

Putting EIPH into perspective

The sight of a racehorse with a nosebleed can be unsettling and raise questions about the animal’s welfare. However, the strict measures in place within the racing industry and continued attention to this condition, should reassure us. The industry is acutely aware of the welfare of these incredible athletes and works diligently to ensure they are cared for at all times.

In summary, nosebleeds in racehorses, while concerning, are a well-documented and carefully managed part of the equine welfare initiatives within the racing industry. The integrity of horseracing rests on its commitment to the welfare and longevity of these remarkable animals.

Sources

Hinchcliff KW. Exercise Induced Pulmonary Hemorrhage In: McGorum BC, Dixon PM, Robinson NE, et al., eds. Equine Respiratory Medicine and Surgery. First Edn. ed: Saunders Elsevier, 2007;617-632.

McKechnie JK, Leary WP, Noakes TD, et al. Acute pulmonary oedema in two athletes during a 90-km running race. SAfrMedJ 1979:261–265.

Hopkins SR, Schoene RB, Henderson WR, et al. Intense exercise impairs the integrity of the pulmonary blood-gas barrier in elite athletes. AmJRespir Crit Care Med 1997;155:1090–1094.

Ghio AJ, Ghio C, Bassett M. Exercise-induced pulmonary hemorrhage after running a marathon. Lung 2006;184:331–333.

Weiler-Ravell D, Shupak A, Goldenberg I, et al. Pulmonary oedema and haemoptysis induced by strenuous swimming. BMJ 1995;311:361–362.

Kline. H., Foreman JH. Heart and Spleen Weights as a Function of Breed and Somatype. Equine Exercise Physiology 1991;3:17-21.

Birks EK, Mathieu-Costello O, Fu Z, et al. Comparative aspects of the strength of pulmonary capillaries in rabbit, dog, and horse. Respiration Physiology 1994;97:235-246.

Sullivan, S. and Hinchcliff, K. (2015) Update on exercise-induced pulmonary hemorrhage. The Veterinary Clinics of North America. Equine Practice, [online] 31(1), pp.187–198. doi:10.1016/j.cveq.2014.11.011.

Hinchcliff, K.W. et al (2005) Association between exercise-induced pulmonary hemorrhage and performance in Thoroughbred racehorses. Journal of the American Veterinary Medical Association, 227(5), pp.768–774. doi:10.2460/javma.2005.227.768.

Tags: EIPH / Nosebleed

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