Taylor Hooton Foundation > Hoot’s Corner > General > Drug Testing in Equine Prepurchase Evaluation
September 22, 2014
Drug Testing in Equine Prepurchase Evaluation
The purpose of a prepurchase evaluation is to determine if a horse is physically suitable for a buyer’s intended use. Communicating the intended purpose of a horse is critical for the veterinarian to do a thorough and appropriate prepurchase evaluation. Drug screening is an important component of the prepurchase evaluation because it can offer additional information pertaining to the ability of the horse to fit the buyer’s needs. When a horse takes medication that can mask pain or injury, or alter behavior or attitude, it’s nearly impossible to assess the horse’s suitability for particular jobs. Although some buyers do not opt for drug screening, many consider it equally important to the rest of a pre-purchase evaluation, as it helps to ensure that the horse they purchased is the horse they expect it to be.

What is the Purpose of a Drug Test?

Drug testing is used for detection of non-steroidal anti-inflammatory drugs (NSAIDs) and/or sedative/tranquilizer agents, but can also be used to detect anabolic steroids and analgesic (pain-relieving) agents. The presence of analgesics could mask current or chronic lameness, while sedatives/tranquilizers are used for behavior modification. The decision to screen for drugs is at the discretion of the buyer. When making the decision to test for drugs, buyers should consider the horse’s intended use, the price of the horse, and any additional information known about the horse’s history.

How Does It Work?

Blood samples (plasma or serum) are most commonly used to screen for drugs as part of a prepurchase evaluation. In some instances, however, urine might be required. The presence of drugs in the sample is detected by ELISA (enzyme-linked immunosorbent assay) or TLC (thin-layer chromatography). An ELISA test, the sample will react with the enzyme, typically causing a color change that will indicate the amount of enzyme bound and, thus, the presence of a drug. A TLC test uses a specialized absorbent plate that will separate different substances as they move across the plate. The resulting marks will indicate which substances are present.

What Do You Test For?

The presence of NSAIDs and behavior-modifying drugs are most common substances owners elect to test for in prepurchase evaluations. Common NSAIDs include phenylbutazone, flunixin, firocoxib, celecoxib, deracoxib, meclofenamic acid, ibuprofen, acetylsalicylic acid, naproxen, and carprofen. Common long-acting tranquillizers are reserpine and fluphenazine. Many other drugs can be tested upon request, including acepromazine, xylazine, diazepam, lidocaine, isoxsuprine, and more. Certain laboratories offer screening for anabolic steroids upon request, but this often requires submission of a urine sample. Anabolic steroids include stanozolol, methandrostenolone, boldenone, nandrolone, and testosterone.

How Long Does It Take to Get the Results?

Basic NSAID screening can be completed in four to five days. Screening for reserpine and fluphenazine takes about five to 10 days. If time is limited, some laboratories offer a 2-day turnarounds for an additional charge. Screening for anabolic steroids requires about seven days. And, if veterinary practices need to send samples to outside laboratories, tests could take a few additional days due to shipping. By Page Bouchard, DVM, University of Tennessee College of Veterinary Medicine (UTVMC) Class of 2014, and José R. Castro, DVM, Dipl. ABVP-Equine, ACVS-LA, UTVMC large animal clinical services instructor.