The thunderous noise of the crowds cheering drowns out the thunder of the hooves coming down the
home stretch as the racehorses, with nostrils raised and flared, glow red against their sweat-darkened hides.
home stretch as the racehorses, with nostrils raised and flared, glow red against their sweat-darkened hides.
Back in the stable afterwards, the trainer notices a drop of blood coming from one his horse’s nostrils and swears.
He has seen this too often. “Dang it! He’s a bleeder.”, he curses.
The public perception is that this is a problem just on the racetrack and for some, just reinforces their concept of how cruel racing can be.
Why this happens we are only beginning to understand. And as our understanding grows, we are discovering that this is a problem that extends far beyond the horses galloping on the racetrack.
But first of all, just what is a bleeder?
Exercise-induced pulmonary haemorrhage (EIPH) refers to the condition in which blood is forced into the airways following exercise. Horses with EIPH can be seen to swallow repetitively following exercise or appear to be in respiratory distress. Very rarely can horses bleed from the nostrils.
“It was generally considered that only few horses experienced “EIPH”, as the occurrence was essentially based only on the appearance of blood at the nostrils (epistaxis). Even today, a horse is classified as a “bleeder” if he or she has profuse amounts of blood in the trachea following training or racing”.
There is a perception that EIPH, or being a bleeder, means “profuse amounts of blood” must be present in the trachea. So the thought is that if there isn’t a profuse amount of blood, the horse is healthy and there is no need for concern. This is not the case, however. As our diagnostics improve, smaller and smaller quantities of blood can be detected and we are finding that these newer lower detection limits are still relevant to the horses’ health.
Just like bowed tendons, EIPH or bleeding is currently commonly thought of as a racing problem. “There has been some debate as to the intensity of exercise required to induce EIPH. Whitwell and Greet (Whitwell and Greet 1984) reported that haemosiderophages were present in the tracheal wash of all horses in training when galloping. More recently, it was shown that lesions consistent with EIPH were present in the lungs at post mortem of 10 out of 13 Thoroughbred horses aged less than two years that had been trained at speeds of only 7-8.5 m/s (420-510metres/min or 16-19 mph) (Oikawa 1999). In addition, EIPH has been recorded in horses following intense trotting exercise (Epp et al. 2006).” (Marlin, 2009).
Also, “A number of endoscopic surveys of EIPH in racehorses have described the incidence (the chance that an individual horse on a single occasion will have blood in the trachea post-exercise) as being between 30-80%. If multiple examinations are made on the same horse, the incidence rises to 82-95%. In one study, all animals examined on three separate occasions after racing had blood visible in the trachea, on at least one occasion giving a prevalence of 100% (Birks et al. 2002).“ (Marlin, 2009).
It is disturbing to realize just how prevalent a problem this is. Something we didn’t know before the introduction of endoscopy. But before we conclude that this is a Thoroughbred racehorse problem, we need to consider that “it is now clear that EIPH occurs in any horse undertaking fast or intense exercise, including Thoroughbred racing on turf or dirt, racing over jumps (hurdle and steeplechase), three-day eventing, polo, barrel racing, reining, roping and cutting, Quarter Horse racing, Appaloosa racing, Arab racing, Standardbred racing (pacing and trotting), show-jumping and even in draught and endurance horses.” (Marlin, 2009).
For the first time we are beginning to realize that EIPH is a problem that goes far beyond the racetrack and can possibly affect any horse, in any discipline, that is undertaking fast or “intense” exercise.
While we need to consider that “the greater the severity of EIPH, the greater the implication for health and welfare. That, even more worrying, we need to consider the cumulative damage to the lungs of the horse.
So what is happening?
EIPH affects the pulmonary circulation, not the bronchial circulation. This is an important distinction because the pulmonary circulation is the de-oxygenated blood coming from the body to the heart and being pushed through the lungs in order to re-oxygenate it. The bronchial circulation is the blood supply that comes from the heart already oxygenated and supplies oxygen to the lung tissue itself. The fact that EIPH affects the pulmonary circulation is important because this reflects on the ability of the horse to acquire oxygen, and this is the reason why some animals go into respiratory
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