Evaluation of ram semen motility by a swim-up technique

The turbidity formed as ram spermatozoa swam up into a clear medium was measured using a colorimeter and this was used as an objective index of sperm motility. Wavelengths of 470-475 nm yielded higher optical densities (OD) than did 520-640 nm. The recommended distance between the light beam and semen-medium interface, and operation temperature were 5 mm and 30-37 degrees C, respectively. Of seven media tested, Tris-glucose was preferred on the basis of results, availability and cost. Diluting semen before testing reduced OD, whereas increasing semen concentration (0.6 to 2.4 x 10(9) spermatozoa ml-1) and the total number of spermatozoa used increased OD. OD gradually increased with time in all experiments (P < 0.001). High positive correlations between OD and known percentages of motile spermatozoa (0.82-0.91 at from 5 to 20 min, all P < 0.001) suggest that this swim-up technique, which is objective and inexpensive, is valid for measurement of sperm motility in rams.