International Screening Limits (ISLs), International Residue Limits (IRLs) and Asian Screening Limits (ASLs) have the purpose to ensure that racing jurisdiction screen therapeutic substances (those which aid in the recovery of the horse) at scientifically agreed and therapeutically active concentrations. In the best interest of our racing, the NHA has historically adopted and applied most of these limits from the International Federation of Horseracing Authorities (IFHA) and the Asian Racing Federation (ARF). Examples of screening limits which are not adopted are those for Phenylbutazone and its metabolite (a drug which is banned for use in this country) and anti-ulcer medications (these are allowed by the NHA to be used within racing).

There are substances which are present in the natural environment, in the horse naturally and / or which are contaminants. Many of these are formalised as International Residue Limits (IRL’s) and these are carefully considered and studied by the NHA for their validity and applicability in this country before these are adopted. It must be noted that Atropine and Scopolamine (drugs substances but potentially also very harmful substances) are not adopted as IRLs by the NHA as these are abnormally high in prevalence in this country within toxic plants which have been shown to at times significantly contaminate local horse feed and roughage.  

Dimethyl sulfoxide (DMSO) is a natural substance (liquid and solvent) found naturally in the horse, as well as in nature and in horse feed such as lucerne (alfalfa hay) and oats.

DMSO is known to significantly increase the permeability (enhance the transport) of certain substances through the skin of the horse and it has additionally been implicated to have some anti-inflammatory effects. In the horse it can be used both topically (on the skin) and injectable (it can be administered by infusion).

Within the IFHA and at the NHA the use of this prohibited substance in the horse has historically been monitored against an International Threshold of prosecution of 15 µg/ml in URINE and 1000 ng/ml (equivalent to 1 µg/ml) in PLASMA.  While the specified concentrations have remained unchanged, DMSO is now instead controlled by International Residue Limits (IRL’s) of respectively 15 µg/ml in URINE and 1000 ng/ml in PLASMA. 

Cobalt is naturally found in the environment, in plants and in the soil. It is present in animals and is a critically required trace element (metal). It is a structural component of Vitamin B12 (which also called Cobalamin), with 4.3 % of the weight of the molecule consisting of Cobalt. 

The NHA recognises the threat which Class 1, Forbidden Substances pose to the integrity of racing and the welfare of the horse. For this reason sophisticated protein and peptide screening methods have been in place at the NHA for close to 20 years. During the year 2000 the NHA Laboratory established collaboration with some other major racing jurisdictions in conducting the initial research and then developing the basis of approaches and methodologies to screen for commercial Growth Hormones (GH’s), their GH releasing precursors, their messenger growth factors and synthetic analogues of such growth factors. The effective screening of a range of different Erythropoietins (EPO’s) which are commercially available was also devised during that time. The range of peptide and protein forbidden substances and substances of concern to racing has since increased and the research and development of screening and confirmation methods for these has not stood still. The NHA has the expertise, experience, set-up and instrumentation required for the screening of such substances. During the racing year 2020/2021 there was screening of such substances employing internationally approved and adopted methodologies. The specimens screened included those from post-race, pre-race and from out of competition collections (unannounced collection of specimens at stable yards). Similar screening is now again in place during the 2021/2022 season.