Modified resazurin reduction test for determining the fertility potential of bovine spermatozoa

The objective of this study was to determine if reduction of the dye resazurin by bovine sperm is associated with the concentration of motile and progressively motile sperm. Metabolically active sperm reduce resazurin (blue color) to resorufin (pink color) and upon further reduction to dihydroresorufin (white color). A total of 68 semen samples from 20 Limousin bulls were collected using electroejaculation. The concentration of motile and progressively motile sperm was determined. Resazurin was added to each semen sample (8.8 microgram/mL semen), samples were then incubated at 37 degrees C for a maximum of 15 min, and visual color changes indicative of dye reduction were noted. Samples were identified as having either low fertility potential (< 200 x 10(6)/mL motile sperm and < 100 x 10(6)/mL progressively motile sperm) or high fertility potential (> or = 200 x 10(6)/mL motile sperm and > or = 100 x 10(6)/mL progressively motile sperm). Assessment of the reduction of resazurin from blue to pink (< or = 3.5 min) allowed identification of 88% of the low and 94% of the high fertility potential samples. In addition, the reduction of resazurin from blue to white (< 15 min) resulted in identification of 82% of the low and 76% of the high fertility potential samples. The modified resazurin reduction test is useful for determining the fertility potential of bovine spermatozoa.