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PSHA - Understanding Foreign Substance



Editor’s Note:
The following document was distributed by the Performance Show Horse Association to help understand the foreign substance debate regarding the Tennessee Walking Horse.  Many member of the public and media have misunderstood the details of the debate and testing conducted in the field.  PSHA hopes the document can help clarify misunderstandings about what a positive foreign substance might indicate.


The Humane Society of the United States (HSUS), and others have attacked the compliance statistics of the industry, based on the percentage of foreign substances found via swabbing the hair on the pasterns (ankles) of horses. What the HSUS and USDA do not disclose in their attacks is that for a swab result to meet the current USDA requirements the area swabbed must be completely sterile, i.e., free of any and all substances and/or contaminates – a standard which is virtually impossible to achieve on a horse’s pastern.

The Horse Protection Act (“HPA”) prohibits the application of foreign substances to a horse’s pastern which are intended to alter the gait of the horse, i.e., irritants, or mask the inspection process. The theory behind the USDA’s swabbing program – which the industry supports – was to identify “irritating, numbing, or masking” substances which had been applied to a horse’s pastern. However, two serious problems exist with the USDA’s current swabbing program, which make all of its results scientifically unreliable and useless for determining whether a horse’s gait has been altered and/or the inspection process masked.

First, despite numerous requests from the industry, the USDA has failed to conduct any scientific study to identify a list of substances, or types of substances, which could be considered irritant or masking agents when applied to a horse’s pastern. Consequently, there exists no scientific evidence that many of the substances identified in the USDA’s results in any way irritate and/or mask a horse’s pastern. By way of example, the USDA has identified a positive finding for Vitamin E and cholesterol as constituting a violation of the HPA. However, both of these substances are regularly found in equine-approved care and treatment ointments and grooming products and there is no evidence that they can be used as an irritant and/or masking agent.

Secondly, again despite numerous requests from the industry, the USDA has failed to establish any type of scientifically accepted “baseline” below which detected substances cannot be said to irritate and/or mask the horse’s pastern. Instead, the USDA has chosen to rely on a scientifically baseless “zero tolerance” policy. The results published by the USDA make absolutely no effort to identify at what levels a substance may have been detected. As a result, there is no determination if a substance may have been present at a level which could have resulted in an irritant and/or masking affect. Once again, the failure by the USDA to apply scientifically accepted principles to its swabbing program render the results useless. 

In 2013, the TWH Industry began its own swabbing program to detect irritant and masking agents and solicited the input and expertise of the AAEP and AVMA with no response. The industry continues to support objective based inspection methods, such as swabbing, which are scientifically reliable. However, the current swabbing program implemented by the USDA provides absolutely no evidence to determine whether there has been a soring violation of the HPA.

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