ESTIMATION OF SPERM VIABILITY IN FROZEN-THAWED SEMEN FROM SWEDISH AI BULLS

From a total of 40 Swedish dairy A.I. bulls, the number of viable sper matozoa in frozen-thawed semen was estimated using a commercial lumino meter (SVT(R)) to determine ATP contents and by fluorescence microscop ic examination of samples stained with the combined fluorophore probes Calcein AM and Ethidium homodimer (CAM/EthD-1). The bulls were of two breeds (24 Swedish Red and White and 16 Holstein) and two age classes (1-2 and 6-10 years old, prior to and after progeny testing, respecti vely). The SVT(R)-instrument was able to estimate a frequency of viabl e spermatozoa (47.0 +/- 14.4 %; means +/- SD) close to that recorded b y the fluorophore probes (spermatozoa with intact plasmalemma and prog ressively motile, 53.6 +/- 11.5 %) and by subjective visual assessment of sperm motility (53.4 +/- 6.0 %). The percentage of motile spermato zoa assessed under phase-contrast was positively (r = 0.33, P < 0.01) correlated with both the total ATP content, the percentage of viable s permatozoa recalculated from the SVT(R) reading (r = 0.26, P < 0.05) a s well as with the frequency of spermatozoa having intact membranes as assessed by CAM/EthD-1 (r = 0.45, P < 0.001). The latter was also sig nificantly correlated (r = 0.59, P < 0.001) with the total ATP content s. No significant variation in ATP contents was present between bulls, breeds or age. A significant difference, however, was seen between bu lls for sperm membrane integrity. The results indicate that the SVT(R) instrument seems to provide a quick and easy estimation of the number of viable spermatozoa in frozen-thawed bull semen. The assessment of membrane integrity with fluorophore probes allows the estimation of sp erm subpopulations within the sample and seems therefore to be more us eful and objective to determine sperm viability than visual assessment of sperm motility.