stallion sperm selection by density gradient centrifugationinvolving a double layer colloid: effects on sperm subpopulation dynamics in fresh and stored semen

sperm selection techniques have became an important tool to improve sub fertile ejaculates. the main aim of this study was to assess the dynamics of motile sperm subpopulations of ejaculates from subfertile stallions subjected to density gradient centrifugation (dgc) involving a double layer colloid [dgc2], before and after storage for 24 and 48 hours. ejaculates from eight stallions with fertility problems were subjected to the different treatments: 1) control [c]; 2) centrifugation [ct]; 3) density gradient centrifugation involving a double layer colloid [dgc2] and 4) post storage density gradient centrifugation involving a double layer colloid dgc2 post]. in the c, ct and dgc2 treatments, sperm variables were analysed at 0 h and after 24 and 48 h of storage at 4-7 ˚c. in the dgc2 post treatment, the semen was stored at 4-7˚cand sperm samples selected by dgc2 at 24 and 48 h. viability, sperm abnormalities and motility were then examined using a computerized system. four motile sperm subpopulations with different motility characteristics were observed in the all treatments. the dgc2 sperm had faster, straighter moving and more active cells at 0 h. at 24 and 48 h, however, the motility variable values fell and the slower spermatozoa subpopulations increased in size. the dgc2 post treatment returned better overall sperm motility variable values at 24 and 48 h; a larger percentage of spermatozoa fell into the faster subpopulations. in conclusion, dgc2 could be used to improve semen from subfertile stallions as well as semen showing poor fertility after storage.