Individual Identification of Racehorses from Urine Samples Using a 26-Plex Single-Nucleotide Polymorphism Assay

To construct a system for identifying individual horses from urine samples that are submitted for postracing doping tests, we developed a genotyping assay based on 26-plex single-nucleotide polymorphisms (SNPs). DNA was isolated from urine using a commercially available DNA/RNA extraction kit, and SNP genotyping was achieved with a SNaPshot (TM) technique. DNA profiles including 26 SNPs were acquired from urine samples and blood/hair samples. Within the studied Thoroughbred population, the 26-plex assay showed a probability of identity of 5.80 x 10-11. Compared to the conventional short tandem repeat assay, the SNP assay used less DNA, and the rate of successful genotyping was improved to 97% using aliquots of horse urine as small as 140 mu L. The urinary DNA could be successfully genotyped under proper storage concerning refrigeration or freezethawing. This SNP assay can be used for individual identification when suspicious results are obtained from horse doping tests.