Observations on the survival of washed boar spermatozoa in different media.

Semen, collected from boars of proven fertility, was concentrated by centrifuging the strained ejaculate at 400 g for 15 min at 20\s=deg\C and gently resuspending the sperm pellet in one-fifth the original volume of seminal plasma. The concentrated semen was then diluted 1:6 either in a chosen wash medium (see Table 1 for composition of media) and used immediately, or in a milk diluent (MFP), cooled slowly to 5\s=deg\C over a period of 5 hr, and stored overnight at 5\s=deg\C. The spermatozoa were washed by centrifugation at 400 g for 12 min followed by gentle resuspension in a fresh aliquot of the chosen wash medium. Three centrifugations were carried out and samples of the final pellet were resuspended in chosen media. All manipulations of fresh semen were carried out at 20\s=deg\C, whereas all manipulations ofstored semen were carried out at 5\s=deg\C, and various combinations of wash medium and resuspension medium were tested. Spermatozoa in the final resuspension media were incubated at 37° C with frequent aeration with a Pasteur pipette, and scored for motility (Emmens, 1947) after 0, 1, 2 and 3 hr by examining a drop of the sperm suspension on a warmed microscope slide under low power magnification in a hot box main¬ tained at 37° C. The identity of each preparation was known to the observer. Cooling boar semen to 5° C at 0-5° C/min caused an irreversible depression of motility. In semen cooled slowly after dilution in MFP, motility was restored on warming. Washing the stored spermatozoa reduced their motility when they were finally resuspended in RFP (Table 1 ). While the use of the sperm-rich fraction (Polge, 1956), or the addition of 2-5 mg bovine serum albumin/ml (Choong & Wales, 1962) or 0-75 mg vitamin E/ml to the SP wash medium did not improve maintenance of motility after washing, final resuspension of the washed spermatozoa in MFP did restore their motility. A further experiment was carried out using, as wash medium, MFP, SE or RFP and, as resuspension medium, MFP, MSP, MRFP, SP RFP or SE (Table 1). Samples of stored spermatozoa were also centrifuged three times and resus¬ pended in their own supernatant as a control. The results (Table 2) indicated that the composition of the final resuspension medium was much more important than that of the wash medium, highly