Improved recovery of frozen-thawed bovine spermatozoa selected via standardized swim-up technique

Abstract

The bovine was used as a model to evaluate the recovery of frozen-thawed spermatozoa via conventional Swim-up and standardized Swim-up (ZSC^TM) technique. Thawed semen specimens (3 bulls) were washed and reconstituted with 2.9% (w/v) sodium citrate extender containing 20% (v/v) chicken egg yolk, and used for selection. The conventional method consisted of overlayering the sperm specimen with isolation media (Ham’s F-10), followed by 1-h of incubation. The ZSC^TM consisted of a conical cavity on the bottom of a glass column into which the sperm specimen was placed until its surface was at the same level as the upper boundaries of a conical cavity. The surrounding periconical and epiconical areas were filled with isolation media, followed by 1-h of incubation. The isolation media was removed from the conventional (80% volume) and ZSC^TM specimens (100%) at the end of incubation (harvesting). Recovered specimens were assessed for volume, percentage and grade of motility, occurrence of osmotic shock, and percentage of spermatozoa reactive to the hypoosmotic swelling test. Conventional and ZSCTM selected specimens were qualitatively similar, but higher numbers of spermatozoa were recovered via the latter (1.6 fold increase). The ZSC^TM method enable recovery of up to 100% of overlayed media and, therefore, of most of the spermatozoa that migrated from the sperm specimen reservoir into the isolation media with no possibility of mixing the two, (as occurs in the conventional method), and contamination of the recovery specimen with dead or immotile spermatozoa was avoided. The ZSC^TM technique enables harvesting of the medium closest to the underlayered sperm specimen, which maximizes sperm recovery. Based on all assessed parameters, the sperm manipulation procedure of choice was clearly ZSC^TM.