Determination of the number of motile sperm within an ovine semen sample using resazurin

Semen samples were collected from 67 post-pubertal Rambouillet rams using e lectro-ejaculation. Only ejaculates containing a volume of greater than or equal to 0.5 mi were tested (n = 121). Prior to addition of the dye, a micr oscopic semen evaluation was performed to assess the number of motile sperm ml(-1) using a Makler counting chamber and a 250x phase contrast microscop e. Resazurin (3.1 mu g) was added to each 0.5 mi sample and incubated for a period of 15 min or until a visible dye reduction from blue to pink could be detected. Samples were maintained at 37 degrees C throughout the test. A ll ejaculates were identified as having at least the minimum average number of motile sperm ml(-1) (greater than or equal to 1.4 x 10(9)), or below th e minimum average number of motile sperm ml(-1) (<1.4 x 10(9)). The sensiti vities, specificities, positive (PPV) and negative (NPV) predictive values and overall accuracies were determined for all samples. The highest sensiti vity was 77% at 15 s and the highest specificity 100% within 13 min. The hi ghest PPV recorded was 93% at 2.25 min and the greatest NPV was 77% at 2.25 min. The highest overall accuracy was 80% noted at 2.25 min. The results s uggest that the reducible dye resazurin is capable of assessing the viabili ty potential of an ovine ejaculate based on the number of motile sperm ml(- 1). (C) 1999 Elsevier Science B.V. All rights reserved.