Discussion

The North American Veterinary Nutraceutical Council defines a veterinary nutraceutical as a 'non drug substance that is produced in a purified or extracted form and administered orally to provide agents required for normal body structure and function with the intent of improving the health and well-being of animals'.
In the UK, regulatory control of nutritional supplements is under EU Food and Feed law. Whilst nutraceutical manufacturers are able to claim benefits to the health of an animal only true medicinal drugs registered with the Veterinary Medicines Directive are allowed to claim a functional effect of treating or preventing disease (Harris 2009).
The VMD only provides a marketing authorisation for a medicinal product once extensive research on efficacy and safety is available. Nutraceuticals claiming strong functional effects on a disease process without possession of a marketing authorisation are in danger of crossing the fine line between 'supplement' and 'drug' often without appropriate clinical or safety trials being available.
Of concern is the belief that if a supplement 'does no good' it probably 'does no harm' however it is important as veterinary surgeons we realise a particular horse may be on numerous nutraceuticals which individually or combined could have side effects. The owner may also feel that the supplements are in themselves sufficient 'treatment' for a condition and fail to call a veterinary surgeon to attend leading to welfare concerns and poor use of an owner's limited budget.
Lack of regulation has lead to claims of wide variation in the levels of 'active ingredient' in some commercially available supplements with many labels failing to state the exact concentrations contained within. In a study of 5 equine glucosamine formulations, 5 chondroitin sulphate formulations and one combined product, glucosamine was found to be present at 63.6% to 112.2% of the label claim and chondroitin sulphate ranged from 22.5% to 155.7% (Trumble 2005).
Nutraceuticals such as glucosamine and chondroitin sulphate are widely used in many species. Popularity of 'joint supplements' in the older horse is understandable as arthritis is a common reason for retirement and indeed euthanasia. Joint supplements are given in the hope of attenuating, stabilising or even repairing articular cartilage in osteoarthritis by supplying the 'building blocks' of cartilage matrix. Certainly studies looking at equine cartilage explants in vitro do suggest glucosamine may provide an anti-inflammatory effect and both glucosamine and chondroitin sulphate may limit glycosaminoglycan degradation and enhance synthesis.
However we require information on the in-vivo efficacy so must consider the bioavailability of the nutraceutical, knowledge of first pass metabolism and actual levels of nutraceutical reaching the target sites (synovial fluid and articular cartilage) when given orally. Current research suggests oral availability of glucosamine and chondroitin sulphate is poor perhaps due to low intestinal absorption and/or first pass hepatic metabolism (Geor 2005).
In vivo trials have been performed in horses but there is often
criticism of the study design due to lack of controls, non-blinding of the assessors and low case numbers. Selection of 'loading' and
'aintenance'doses is often without clinical justification.
Lightly dismissing a product which when given orally could have a strong beneficial effect on the cartilage of an older horse would be highly inappropriate. However fully independent, well designed clinical trials with statistically significant case numbers and data for short- and long-term use are essential along with the reassurance of guaranteed product analysis.