Assessing the fertility potential of equine semen samples using the reducible dyes methylene green and resazurin

The objective of this study was to determine if spermatozoal reduction of the dyes methylene green to colorless and resazurin to pink or colorless was associated with the fertility potential of an equine semen sample. Fifty samples from 38 stallions were evaluated for the number of spermatozoa per milliliter and number of motile sperm per milliliter. Methylene green (20 mu g/mL of semen) or resazurin (85 mu g/mL of semen) was added to 3-mL, aliquots of semen. Semen samples were identified as having low fertility potential (<200 x 10(6) total cells/mL and <140 x 10(6) motile cells/mL) or high fertility potential (greater than or equal to 200 x 10(6) total cells/mL and greater than or equal to 140 x 10(6) motile cells/mL). The sensitivities were 80% for the methylene green, 68% for the resazurin to pink, and 60% for the resazurin to colorless tests. The specificities were 80% for the methylene green, 79% for the resazurin to pink, and 92% for the resazurin to colorless tests. The overall accuracies were 80% for the methylene green test, 74% for the resazurin to pink test, and 76% for the resazurin to colorless tests. The methylene green and resazurin reduction tests can provide valuable information on the fertility potential of an equine semen sample.