Assay of sperm quality in the domestic fowl by MTT reduction.

1. An assay which measures the capacity of spermatozoa from the domestic fowl to reduce the colourless tetrazolium dye MTT to its highly coloured purple formazan pigment has been developed and characterised. 2. The assay has several advantages over a previous tetrazolium-based sperm quality assay: it functions without the unstable phenazine methosulphate and toxic cyanide reagents and, following the reductive reaction, the sperm suspension is solubilised to produce optically clear solutions without centrifugation. 3. For samples of semen from individual males, MTT-reduction is strongly correlated with INT-reduction, which has been previously shown to be a useful predictor of sperm fertilising ability.