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Is EIPH beyond the scope of dietary change?

NUTRITIONWeb Master
  Is EIPH beyond the scope of Dietary Change?       Exercise induced pulmonary haemorrhage has been a concern to trainers for a very long time. The historic record of EIPH in horses such as ‘Bleeding Childers’, a son of the Darley Arabian, a founder of the modern thoroughbred, shows that ‘bleeding’ as it is commonly known is an age-old problem. The prevalence of EIPH during high intensity exercise,  such as racing, is relatively high, but influenced greatly by how it is diagnosed. For example, the prevalence of EIPH is quite low when the appearance of blood from the nostrils (epistaxis) is used as the diagnostic criteria. Unsurprisingly, it is much higher when more rigorous investigative techniques such as endoscopy or bronchioalveolar lavage are used.  Additionally, the prevalence increases when horses are repeatedly examined. In clinical terms, it has been suggested that if you look hard enough diagnostically, and often enough, almost all horses will show a degree of EIPH with racing at some time.  A large Australian study has also reported that there is a proven heritability or genetic element to this condition.       Notwithstanding this, EIPH presents a major concern for horses in training, as it often leads to loss in training days and may impact on race performance, although this seems to be dependent on the degree or grade of EIPH involved. A period of absence from the racecourse can also be a requirement of some racing jurisdictions, e.g. the British Horseracing Authority in the UK, following epistaxis, where blood is seen visually from one or both nostrils. Public perception is also relevant, especially when the public mood puts racing under tighter scrutiny in terms of animal welfare. There is also a mood for change with regards to the previously widespread use of pre-race medications, such as furosemide, (which has been widely used to treat EIPH) in countries such as the USA.  The Arabian Racing Organisation has recently announced that it will become ‘Lasix-free’ in the USA, which has been widely welcomed by trainers worldwide.        In some racing jurisdictions, nasal strips can be used which support the tissues of the nasal cavity helping to keep the upper airway fully open during exercise. There is evidence to suggest that nasal strips reduce upper airway resistance. Some prominent veterinarians and exercise physiologists have proposed that there is sufficient scientific evidence to support their use in the management of EIPH. However, despite being a non-invasive tool their use is not currently allowed in all racing jurisdictions including in the UK.       Whilst there is always a drive to discover new medications that will effectively control or treat EIPH within the rules of racing, diet and other complementary practices have always been of parallel interest to trainers.       The central paradigm to EIPH is that the membrane layer that exists between the alveolar air and the blood vessels is miniscule, representing a physiological cliff edge. This membrane must be sufficiently thin to allow efficient gas exchange, but this makes it very vulnerable to physical damage when under increased physiological stress, e.g. during hard work and racing when a massive increase in gaseous exchange is required.        From previous published research, EIPH seems to be a progressive disease, with time in racing being a significant factor. A current theory is that there is a progressive narrowing of the pulmonary veins, as a result of strengthening of these vessel walls due to smooth muscle expansion or hypertrophy, as well as collagen deposition in the vessels themselves.  Interestingly, in human studies where pulmonary hypertension (high blood pressure in the vessels supplying the lungs) exists, medics have also described calcium deposits or plaques in the pulmonary vessels, which would contribute to a loss of elasticity. This was also investigated in horses in a Canadian study of 108 racing horses that had died or were euthanized. In this study, the authors found a high presence of calcium deposition within the tunica media (muscular middle layer) of the pulmonary arteries.        My interest of course is due to the dietary implication of this theory and it may be an example of barking up the wrong ‘vitamin tree’. Vitamin K has featured for many years in supplements seeking to nutritionally address the issue of EIPH in the miss-held belief that inappropriate clotting is involved in its mechanism. Vitamin K has a well-defined role in clotting and largely synthetic forms of vitamin K (menadione) have been employed in equine nutrition to ‘solve’ this non-issue. However, vitamin K also has a central role to play in calcium homeostasis by activating GLA proteins in the body, including osteocalcin and matrix GLA protein.  Matrix GLA protein is responsible for scavenging calcium from areas of unwanted deposition such as blood vessel walls and soft tissue and driving its repatriation back into bone.  ‘Dr Green’ seems to be on the case again, as vitamin K1 (phylloquinone), the predominant natural source of which is actively growing green pasture, holds the key to activation of these GLA proteins in horses. The widely used synthetic vitamin K or menadione does not exhibit this function. It would certainly be interesting to see whether activation of GLA protein is sub-optimal in EIPH-positive horses compared to EIPH-negative horses. Fresh and actively growing grass is of course notably absent from most racing diets, with the exception perhaps of places like New Zealand. It is also noteworthy that vitamin K1 in the normal diet is unstable and is rapidly lost from pasture that is converted to hay or haylage or other harvested forage (see previous European Trainer article, Vitamin K- the forgotten vitamin).         The overarching focus of nutrition in relation to EIPH has been to tackle perceived pinch points, or potential weakness, in the horse’s physiological systems that may contribute to the expression of EIPH. Typical areas for focus have been collagen synthesis, blood clotting, inflammation, respiratory challenge, water balance and haemodynamics. Given that at the current time research scientists do not have a definitive explanation of the mechanism or aetiology for EIPH and there are no treatment options with 100% certainty, it is difficult to see how a simple dietary intervention could prevent EIPH in isolation. However, nutrition offers a relatively benign method to potentially reduce some of the risk factors that may be involved in the expression of EIPH and potentially reduce its severity.         Vitamin C, either in isolation or in combination with other nutrients with antioxidant activity, has also been looked at in relation to airway inflammation and capillary fragility which could be regarded as risk factors for EIPH. Vitamin C is the main water-soluble antioxidant found in lung lining fluid and is also required for a key stage in collagen synthesis, which adds strength to blood vessel walls. Whilst no direct benefit of vitamin C on the instance of EIPH has been reported, there are several studies which suggest an improvement in airway inflammation as a consequence of supplementation. Certainly, as part of a multifaceted approach, normalisation of airway inflammation must surely be beneficial. However, supplementation is not necessarily the answer, as a good racing diet should provide sufficient antioxidants and their co-factors and horses do not have a dietary requirement for vitamin C under normal circumstances. However, clinical need supplementation with a bioavailable form of vitamin C may be a benefit.       Airway inflammation is certainly an issue in horses in training and any measure to normalise this should be beneficial. A low-dust environment, high-quality feed and forage with a microbiological fitness to feed being essential. Feeding haylage or hay, in conjunction with an appropriate proven protocol for steaming will also help to reduce the drivers of airway inflammation to which horses in training can be exposed.        Nitric oxide is a vasodilator through its action in relaxing vascular smooth muscle and it is produced locally by the action of nitric oxide synthase. Some feed supplements have drawn on this action to suggest the benefit of various ingredients that act as precursors or stimulants of nitric oxide synthesis, although, a clinical trial to investigate the effect of inhalation of nitric oxide resulted in a negative effect on EIPH.         Omega 3 fatty acids have been investigated for their ability to increase the fluidity, flexibility or ease of travel of red blood cells through blood vessels, which could potentially reduce resistance to the flow of blood during exercise. Additionally, omega 3 fatty acids are anti-inflammatory in nature compared to their omega 6 counterparts, which may also have some beneficial effect on airway inflammation. There have been three studies now published in horses that suggest that supplementation with long chain fatty acids DHA and EPA can at least reduce the severity of EIPH. The omega 3 fatty acid content of a racehorse’s diet is normally quite low, as pasture represents one of the most significant sources under normal conditions.  Analysis of Ryegrass, Fescue and Orchard grass in Canada has shown that the parent omega 3 fatty acid alpha linolenic acid is quantitatively the most significant fatty acid in pasture.  However, the conversion of linolenic acid to the physiologically more functional DHA and EPA is relatively inefficient at about 5% conversion. Other ingredients such as salmon oil, tuna oil and certain algae can offer a richer source of DHA and EPA, although this must be balanced against the volume of pasture and hence linolenic acid that could be potentially be consumed by a horse at pasture for part of the day.       In summary, it is very unlikely that there are any nutritional panaceas for EIPH at present, or on the horizon. However, there are a few practices and nutritional factors, which collectively under veterinary supervision may help to move horses at risk of EIPH a little further away from the proverbial cliff edge. In addition, the availability of pasture, in terms of omega 3 and vitamin K1 intake, as well as the beneficial effect of a non-stable environment on airway inflammation should perhaps be investigated further in horses at risk of EIPH. However, given the suggested genetic component to this disease the question of desirability perhaps needs to be asked in parallel.        
 

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Exercise induced pulmonary haemorrhage has been a concern to trainers for a very long time. The historic record of EIPH in horses such as ‘Bleeding Childers’, a son of the Darley Arabian, a founder of the modern thoroughbred, shows that ‘bleeding’ as it is commonly known is an age-old problem.

The prevalence of EIPH during high intensity exercise,  such as racing, is relatively high, but influenced greatly by how it is diagnosed. For example, the prevalence of EIPH is quite low when the appearance of blood from the nostrils (epistaxis) is used as the diagnostic criteria. Unsurprisingly, it is much higher when more rigorous investigative techniques such as endoscopy or bronchioalveolar lavage are used.  Additionally, the prevalence increases when horses are repeatedly examined. In clinical terms, it has been suggested that if you look hard enough diagnostically, and often enough, almost all horses will show a degree of EIPH with racing at some time.  A large Australian study has also reported that there is a proven heritability or genetic element to this condition.

Notwithstanding this, EIPH presents a major concern for horses in training, as it often leads to loss in training days and may impact on race performance, although this seems to be dependent on the degree or grade of EIPH involved. A period of absence from the racecourse can also be a requirement of some racing jurisdictions, e.g. the British Horseracing Authority in the UK, following epistaxis, where blood is seen visually from one or both nostrils. Public perception is also relevant, especially when the public mood puts racing under tighter scrutiny in terms of animal welfare.

There is also a mood for change with regards to the previously widespread use of pre-race medications such as furosemide (which has been widely used to treat EIPH) in countries such as the USA.  The HH Sheikh Mansoor Bin Zayed Al Nahyan Global Arabian Horse Flat Racing Festival had recently announced that its races in the US will be ‘lasix-free’, which has been widely welcomed by trainers worldwide.

In some racing jurisdictions, nasal strips can be used which support the tissues of the nasal cavity helping to keep the upper airway fully open during exercise.

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