Effect of split ejaculation and seminal extenders on longevity of donkey semen preserved at 5° C

The aim of this study was to evaluate the longevity of donkey sperm comparing the rich seminal fraction and the whole semen in two extenders, Kenney and modified Baken extenders. Semen of five donkeys were collected through an open-end artificial vagina once a week for five consecutive weeks. The two first jets (rich fraction) of semen were collected separately from the rest of the ejaculate. Whole semen samples were obtained mixing proportionally part of the rich with part of the poor seminal fractions. Seminal samples were immediately diluted 1:1 in each extender and maintained at room temperature during sperm concentration analysis. Samples were further diluted to rich 50×10(6) sperm per ml, cooled in a refrigerator at the initial rate of -0.6° C/min and preserved at 5° C. Total motility (TM), progressive motility (PM) and sperm vigor (V) were examined after final dilution and cooling, and every 24 hours up to the decrease of total motility under 10%. Sperm morphology was evaluated using a phase contrast microscope directly after dilution, on days 3, 6 and 9 post collection. It was used a 2×2 factorial design in a randomised bloc experiment, and means were compared by Student?s t test. Longevity did not vary between the rich seminal fraction and the whole semen for both extenders used. TM, PM, V and sperm morphology were better preserved in the extender with egg yolk (modified Baken extender) than in the one with skimmed milk (Kenney) in both seminal fractions.