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Immunological role of Aloe vera in thoroughbred racehorses

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01 September 2015, at 1:00am

DAVID URCH traces the history of the plant whose herbal healing properties have been known through the ages but which has proved controversial – and reviews some of the current trials on horses

THERE are written records of Aloe vera being used to improve the health of animals going back 4,000 years. In 2100 BC the first mention of veterinary science was alluded to in the “laws of Hammurabi” and in the same year the medicinal properties of Aloe vera were recorded on Mesopotamian clay tablets.

The first Aloe vera to arrive in the UK was in 1693, most coming from Jamaica and known as “Cape” or “Horse Aloes”.

In 1844 the veterinary schools were granted a royal charter to become the Royal College of Veterinary Surgeons. Aloe vera was such an important herb to the veterinary profession at this time that it was included in the RCVS coat of arms which still shows a centaur carrying a shield bearing a picture of the Aloe vera plant.

Context

Race and performance horses are subject to considerable stress within their training and management programmes. It has been well reported (Murray, 1996) that as many as 90% of racehorses in training and 60% of performance horses suffer from gastric ulcers.

At the same time these stresses and exposure to infections can compromise the horses’ immune systems, leading to conditions such as equine chronic fatigue syndrome (Green, 1996; Watson, 2009).

Clinical evidence and some research has suggested that Aloe vera has two major clinical benefits on both the immune system and epithelial tissues. Green (1996) and later Atherton (1997) proposed that Aloe vera was an immunomodulator, principally due to its polysaccharide constituents. One polysaccharide in particular, Acemannan, which is composed of glucose and mannose, may even stimulate the immune system to increase antibody production.

Acemannan is absorbed intact from the small intestines through pinocytosis and circulates in the blood unchanged. Acemannan increases the release of the cytokine interleukin and prostaglandins from macrophages as well as increasing their phagocytic activity.

Acemannan is also engulfed by T-lymphocytes which stimulates them to release cytokines which encourages B-lymphocytes to increase antibody production.

There is some debate over the optimal molecular size of the polysaccharides present in Aloe vera, but research has indicated that it is between 4 and 7 million Da (Pugh et al, 2001; Sun-A Im et al, 2005). The polysaccharides of this molecular size have been shown in both vitro and vivo to have diverse immunomodulatory properties (Reynolds et al, 1999).

This clinical study was set up to investigate whether Aloe vera could help to maintain the immune systems of race horses in training, by monitoring changes in globulin levels. An increase in globulin levels is an indicator of enhanced immune status.

I have found to produce consistent results, the Aloe vera needs to be filleted, resulting in a formulation comprising mainly the parenchyma cells and mucilage, with a low sap content.

It is also important to source the herb from a company which grows the herb, bottles and distributes it, and a source which is able to certify full traceability. The gel must also have been independently tested by the HFL Sports Science Laboratories and certified not to contain prohibited substances.

Method

A group of 37 horses of various ages and sex was enlisted for the trial. Management remained the same throughout the trial period and the horses received no other feed supplements. The horses were all steeple chasers and continued to be transported to race meetings in various parts of the country.

Of the 28 horses which completed the trial, 19 had been given 120ml of Aloe vera gel daily for 12 weeks and nine were used as controls. Bloods were tested at the beginning of the trial and then monthly.

Routine haematology was carried out on the samples, with total serum proteins and globulin levels being of particular interest. Like most racing yards, during the trial period the horses were exposed to the usual respiratory tract infections and musculoskeletal problems which led to the withdrawal of nine horses of the original 37 from the trial.

Results

Of the 19 horses given 120ml Aloe vera gel daily, 18 (95%) had total serum proteins within normal range at the end of 12 weeks and 10 (53%) of the 19 showed an increase. In 13(68%) of the 19 horses there was an increase in globulin levels. All total white blood cell counts were within the normal range by the end of the trial. Of the nine horses that completed the trial but received no Aloe vera gel, four (44%) showed an increase in total serum proteins while only three (33%) had increased their globulin levels (Table 1).

Conclusion

Drawing specific statistically significant conclusions from small and basic clinical trials like this is difficult. What this trial has done is to identify trends which indicate that Aloe vera gel may have a role to play in helping to maintain a horse’s immune system under the stresses of racing.

A helpful finding which supports earlier clinical trials and my previous experience is that horses require a minimum volume of 120ml Aloe vera daily and for at least 12 weeks before consistent benefits become apparent. Furthermore when trying to help specific conditions of the immune system such as post-viral lethargy syndrome I have found that at least 250ml is required daily.

Even at this lower level 95% of the horses had normal total serum proteins with 53% showing an increase. The globulin levels were increased in 68% of the horses on gel while nine of these showed over a 16% increase. In the horses which did not receive gel, only 33% showed an increase in globulin levels.

This study supports earlier reports (Lunn and Rush, 2004) that natural products can also stimulate immune function in horses with the additional benefit that this herb contains no prohibited substances.

References

Murray, M. J. et al (1996) Factors associated with gastric lesions in thoroughbred racehorses. Equine Veterinary Education 28 (5).

Green, P. (1996) Aloe vera extracts in equine veterinary clinical practice. Veterinary Times 26. Watson, T. (2009) Chronic fatigue syndrome in horses. Veterinary Times (8).

Atherton, P. (1997) The Essential Aloe Vera – the actions and the evidence.

Atherton, P. (1997) What is Aloe vera? British Journal of Phytotherapy 4 (4): 76-83.

Pugh et al (2001) Characterization of Aloeride, a new high-molecular-weight polysaccharide from Aloe vera with potent immunostimulatory activity. Journal Agric Food Chem 49: 1,030-1,034.

Sun-A Im et al (2005) International Immunopharmacology 5: 271-279.

Reynolds and Dweck (1999) Aloe vera gel leaf: a review update. Journal Ethnopharmacol 68: 3-37.

Lunn, D. P. and Rush, B. R. (2004) Immunomodulation in horses: principles and mechanism. Proceedings of 50th Annual Convention of the American Association of Equine Practitioners.