Feed contaminants - how big a risk are they?

By Dr Catherine Dunnett and Dr Mark Dunnett

For all professionals associated with the training and competition of horses under the rules and regulations of racing, the choice of which feed products to use has never been greater, and the range appears to grow on a daily basis.  This is especially true of the plethora of dietary supplements (otherwise known officially as complementary feeds) available.

Feeds and other contemporary nutritional supplements are not pure products in the same manner that veterinary pharmaceuticals are and thus they will, in a traditional sense, contain foreign substances, even though this is commonly only at trace levels that will have no discernible effect on the horse. Numerous harmful or undesirable substances can potentially contaminate the equine diet, whether manufactured feeds and supplements, or grazing and preserved forages. 

These dietary contaminants can be divided into groups including heavy metals, non-metallic toxic elements, pesticides, mycotoxins, plant toxins, and pharmacologically/physiologically active substances that are considered prohibited or foreign substances within the horse under racing rules and regulations.  There is some crossover between plant toxins and prohibited substances, but it is the latter category that concerns us within this article.

Prohibited (foreign) substances
Under the framework of the International Federation of Horseracing Authority's International Agreement on Breeding, Racing and Wagering, Article 6, a prohibited substance is described as  -
"…substances capable of giving a horse an advantage or being disadvantaged in a race, contrary to the horse's inherent merits."

Article 6 further defines prohibited substances as- "

Substances capable at any time of acting on one or more of the following mammalian body systems:

•    the nervous system

•    the cardiovascular system

•    the respiratory system

•    the digestive system

•    the urinary system

•    the reproductive system

•    the musculoskeletal system

•    the blood system

•    the immune system, except for licensed vaccines against infectious agents

•    the endocrine system

•    Endocrine secretions and their synthetic counterparts

•    Masking agents

In broad and simple terms, a prohibited substance can be described as any substance (usually but not exclusively drugs/medicines) that has been given to a horse in its feed, or by any other means, that can exert an effect upon the horse.
Certain factors make the presence of prohibited substances as contaminants in the production of equine feedstuffs almost inevitable. 

Analytical techniques employed are increasingly sophisticated and sensitive and this latter fact serves to increase the likelihood of the detection of contaminants at levels that have been historically unattainable.  Furthermore, the increasing diversity of dietary supplements leads to the introduction of unusual components into the equine diet.  This is particularly the case with products that contain herbs or plant derivatives or extracts.

Additionally, there is increased sourcing of feedstuff raw materials from previously unaccessed regions of the world where quality control measures may be below the desirable standard and where novel crop infesting plants may be found. 

Contamination in compounded equine feeds and raw materials is varied, but the major sources can be categorized as follows:

Endogenous, natural feed constituents     

Salicylates, DMSO
Ubiquitous environmental contaminants   

Transport contamination of raw materials Caffeine, theobromine
Manufacturing cross-contamination     

Crop contamination by invasive plants   

 Morphine, atropine
Racing yard feed contamination         

Veterinary medication

The most commonly encountered prohibited substances in equine feedstuffs include salicylates, dimethylsulphoxide (DMSO), caffeine and theobromine, morphine, hyoscine, atropine and hordenine.  There are however, a considerable number of pharmacologically active compounds potentially present in manufactured feeds, grazing and preserved forages that will be viewed as prohibited substances. Examples of these are listed in the table below, however the list is indicative rather than exhaustive.

Prohibited substances potentially present in feedstuffs and grazing:

Prohibited substance   


Salicylic acid    Alfalfa (Lucerne), willow
Dimethylsulphoxide (DMSO)    Alfalfa, others
Caffeine    Coffee
Theobromine    Cocoa
Theophylline     Coffee, Cocoa
Morphine    Poppy
Codeine    Poppy
Hordenine    Germinating barley, Phalaris grasses
Hyoscine    Belladonna plant species
Atropine    Belladonna plant species
Lupanine    Lupin seed
Bufotenine    Phalaris grasses
Valerenic acid    Valerian
Dicoumarol    Spoiled sweet clover
Borneol    Carrots, wood shavings
Camphor                Rosemary

Unlike in the US, in Europe it is common practice for feeds and supplements to be tested by their manufacturers for potential contamination with prohibited substances before being released for sale.  This practice is particularly evident for those products marketed to the performance sector.  Typically, the service offered by laboratories such as HFL Ltd in the UK and the Laboratoire Des Courses Hippique (LCH) in France screens for the presence of commonly recognized feed contaminants which includes:

Contaminant        ARCI Classification† 
Morphine        UK/France    1
Hyoscine        UK/France    3
Atropine        UK/France    3
Hordenine        UK/France    Not stated*
Caffeine        UK/France    2
Theobromine        UK/France    4
Theophylline        France    3
Bufotenine        France    Not classified/not actioned
Methylbufotenine        France    Not stated*
Dimethyltryptamine        France    Not stated*

? ARCI classification defines the regarded severity of a positive post-race test with these contaminants which will affect the severity imposed, with class 1 being the most severe.*Presumably, these would be regarded as being akin with bufotenine as they can all be associated with Phalaris grasses.
Such pre-sales laboratory analysis is not common for US feed manufacturers.

To some extent this may reflect a reduced risk of contamination of feed with naturally occurring contaminants such as these above, due to less importation and transportation of raw materials.

 Natural feed constituents
 Salicylates and dimethylsulphoxide (DMSO) are present in numerous feed ingredients and pasture species.  Salicylates are particularly abundant in grazing and forage legumes, such as clover and alfalfa respectively, and in willow-containing herbal supplements. 

Plant salicylates are metabolized in the body to salicylic acid, a mild pain killer (analgesic) and anti-inflammatory.  Salicylic acid is a metabolite of Aspirin.  DMSO occurs at high levels in alfalfa and is also a weak analgesic and anti-inflammatory. DMSO can be used to enable other drugs to penetrate the skin. Owing to their widespread occurrence and pharmacological properties, international racing jurisdictions have established thresholds for their presence in post-competition urine and blood samples.  In itself it is unlikely that feed-related salicylate load will cause testing thresholds to be exceeded and feed products are not tested to identify the presence of these substances.

Hordenine and bufotenine are recognized as occasional contaminants of equine feedstuffs.  Both substances are constituents in Phalaris grass species (Reed Canary grass), and hordenine also occurs in germinating barley and other cereal grains. 

Hordenine and bufotenine affect the central nervous system (CNS) of horses and are thus are regarded as prohibited substances under racing rules. They have both been detected in post-race urine samples across the US, Europe and Australia  

Feed crop contaminants
 Morphine and codeine present a less common but significant feed contamination issue.  Their presence in post-race samples is a breach of prohibited substance rules as they can exert a significant stimulatory effect in the CNS of horses even at low doses.

During the last decade post-race urine samples have tested positive for opiates in the US, Australia, the UK and Ireland.  Whilst the route of contamination has not always been established, feed contamination with material from opium poppies (Papaver somniferum ssp. somniferum), wild poppies (P. somniferum ssp setigerum) or ornamental poppies (P. Orientale) is likely due to the use of contaminated raw materials.
The alkaloids hyoscine (scopolamine) and atropine are also known contaminants of horse feed that derive from contamination of growing cereal crops by Solanaceous plants including Deadly Nightshade, Henbane and Jimson Weed.  Deadly Nightshade (Atropa belladonna) contains predominantly atropine, whereas Henbane (Hyoscyamous niger) contains primarily hyoscine. Owing to their potent pharmacological effects within the central nervous system and cardiovascular system, the presence of hyoscine or atropine in post-competition urine samples is regarded as a breach of the rules relating to prohibited substances. 

Manufacturing and shipping contamination

Caffeine and theobromine are recognized contaminants of feeds and numerous instances of feed contamination and post-race positives occurred globally during the 1980s and 1990s.  In the past, cocoa husk was used as a bulking agent in feed manufacture however, more recently its presence in feeds is believed to have arisen from contamination from other feed residues, such as biscuit meal or from contamination of raw materials, usually grains, during transport. 

We are all aware of caffeine as a constituent of coffee and tea, whereas its chemically similar cousin theobromine is found naturally in tea and cocoa (chocolate). When ingested, both substances can act as stimulants to the heart, lungs and brain, and may also exert some degree of diuretic action (increased urination). As a consequence of the prevalence of caffeine and theobromine in the feed production chain and the difficulty in removing them, racing's regulatory authorities worldwide have largely implemented a threshold for theobromine in post-race urine samples. 

In the recent past in the US mepyramine, an antihistamine, has been identified in post-race samples and its appearance on these occasions was attributed to contaminated vitamin preparations. 

Procaine, a local anaesthetic, has also been implicated in post-race positives on a number of occasions where on further investigation the source was discovered to be horse feed cross-contaminated at the mill with pig feed containing the antibiotic procaine penicillin.  

Environmental contamination
Arsenic is a prohibited substance under equine competition rules, but as it is a ubiquitous environmental substance, a threshold level has been established for its presence in post-competition samples. 

Additionally, arsenic levels in the racing environment can be increased by contamination from the use of pesticidal arsenic compounds, the most commonly encountered being wood preservatives used to treat construction timber and fencing materials.  

Many veterinary drugs used therapeutically in a racing environment are formulated as powders so they can be administered mixed in with normal feeds. 

Although this is a convenient method in contrast to a reliance on injections for example, it can present a significant risk of dietary contamination to horses other than the animal under treatment if shared feeding equipment is not kept scrupulously clean.  Dusts from some drug formulations can contaminate and linger on surfaces in feed rooms, mangers or stables. 

Certain drug formulations including isoxsuprine, clenbuterol and flunixin, can present a particular problem in this regard.
Dietary supplements
Racing is first and foremost a business, with the end-point being to maximize race wins and prize money and hence hopefully to increase future income from training fees.  It is consequently understandable that any legitimate dietary approach which might benefit race performance and training capacity, or reduce the incidence of illness and injury, and accelerate recovery both from racing and ill health, might at the very least be evaluated. 

This search for an ‘edge' is common to business and sport.  Indeed, the perceived beneficial effects of dietary supplements in human sports have been to some extent translated to equine sports including racing. 
The increased availability of dietary supplements for horses can often be supported by sophisticated technical marketing and detailed scientific research. 

But, whatever the motivation for the use of such products might be, whether backed by rigorous evidence of efficacy or not, the reality is that complementary feedstuffs are also potentially at risk of contamination.  Although there has been no comprehensive survey of contamination in equine feed supplements, three such surveys have been conducted on human sports supplements, the results of which indicated that up to 20% of supplements tested contained prohibited substances (under IOC rules), principally anabolic steroids including nandrolone and testosterone. 

As the levels of contaminants found were generally low and variable it was assumed that their presence arose through poor manufacturing practice on the part of the manufacturer or the ingredient supplier(s).  Undeclared stimulants, such as caffeine and ephedrine, have also been identified in human sports supplements and these findings suggest deliberate adulteration to improve efficacy. 

A recent doping case suggests that equine supplement contamination may become an issue for the feed and supplement industry and regulatory authorities, but on this occasion this post-race positive for the presence of the anabolic nandrolone seems to have arisen through the use of a human sports supplement in the horse, rather than a contaminated equine product.

The use of dietary supplements in racing is becoming commonplace.

Products containing herbal or other plant based or nutraceutical ingredients are increasingly popular, possibly through a belief that these are not drugs and thus do not infringe the rules relating to prohibited substances. A useful example here would be products containing Devil's Claw powder or extracts.  Devil's Claw is a plant related to Sesame and is native to southern Africa. It has recognized pain-relieving and anti-inflammatory properties in people and has been offered as an alternative to established over-the-counter pain relief medicines, such as Aspirin, paracetamol and ibuprofen, for many years, and is currently undergoing clinical trials.

Widespread promotion of Devil's Claw, as an herbal alternative to phenylbutazone for horses, began at a time when the continued approval for the use of this veterinary pain-relieving drug was in doubt.  It is worth pointing out that the French racing laboratory, Laboratoire Des Courses Hippiques, have recently published methods for the detection of harpagosides, the active components in Devil's Claw, in equine post-race samples, and thus is it reasonable to assume that US regulatory laboratories may be screening for these substances.

The irony here is that, when viewed within the strictures of the rules and regulations of racing, if a supplement, or more accurately one or more of its constituents, has efficacy, by extrapolation it must affect one of the horses' body systems and is therefore prohibited, whether or not the laboratory is able to test for it.

Trainer protection
We should not be complacent on this issue and it would be prudent for trainers, wherever practical, to retain representative samples of all batches of feeds and supplements that they use, indeed the regulatory authorities proffer just such advice. This is certainly a worthwhile exercise, as in the event of a failed post-race test a defense of feed contamination will be strengthened by such physical evidence, which can be subjected to analytical scrutiny. 

In practice, a successful demonstration of contaminated feed or supplement will not exonerate the horse's connections from a regulatory offense, but may well be a persuasive argument in mitigation concerning subsequent sanctions.
In addition, being fully aware of the ingredients within feeds or supplements and of the nature and extent of any pre-sale quality assurance analysis by a manufacturer for the common contaminants (prohibited substances) should afford trainers some further protection and allow them to make informed purchases.

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