The Effect of Four Different Commercial Semen Extenders on the Motility of Stallion Epididymal Sperm

To preserve epididymal sperm, only a limited number of sperm is available, and an optimum processing method that is applicable for the majority of stallions is therefore crucial for successful preservation. The aim of the present study was to evaluate the effect of four different extenders that are commercially available for chilled semen on the motion characteristics of stallion epididymal sperm. Sperm were harvested by retrograde flush from 20 epididymides after the routine castration of 10 stallions. Aliquots of sperm samples were diluted with each of the four extenders ([E1] skim milk-based, [E2] containing defined milk protein, [E3] containing egg yolk, and [E4] containing caseinate). Total motility (TMOT %) and progressive motility (PMOT %) assessed immediately after sperm harvesting and during prolonged storage were highest in extenders with selected milk proteins (E2: 54, 24-79 and 50, 19-78; E4: 57, 23-82 and 52, 14-80) compared to the skim milk-based extender (E1: 40, 1-66 and 37, 0-62) and the egg yolk-containing extender (E3: 21, 6-48 and 13, 2-40; median, min-max for TMOT and PMOT, stored for 48 hours at 4°C, respectively). Motility values were similar for extenders E2 and E4 during the entire storage period (P > .05), while extenders E1 and E3 yielded significantly lower values (P < .05). Using E1, motility increased during the storage period but did not reach values similar to those of E2 or E4. Curvilinear velocity (VCL), amplitude lateral head displacement (ALH), and beat-cross frequency (BCF) differed among all extenders after sperm harvesting (P < .05), but not after 24 (VCL, ALH) and 48 hours (VCL, ALH, BCF; P > .05). Based on the motility results, we recommend extenders containing defined milk protein to process epididymal sperm.