Impairment of ram sperm-hyaluronan binding ability by the freezing extender

The ability of ram sperm to bind to hyaluronan coated slides (HBS, %) was tested on fresh (FS) and chilled semen (CS) diluted with skimmed- milk based extender (CS-SM), chilled (CS-EY) and frozen-thawed (FTS-EY) semen diluted with tris-glycerol-egg-yolk based extender. The % of HBS (motile bound sperm/all motile sperm) was similar in FS and CS-SM groups (73,6 % vs. 71,2 %) both significantly higher than CS-EY (25 %) and FTS- EY (29,7 %) groups. Progressive individual motile sperm (IMS) of the FTS-EY group was the lowest (21,7 %), and no differences were found among FS (63,3 %), CS-SM (55 %) and CS-EY (48,3 %). IMS was positively correlated with HBS (r= 0,62; p<0,03). Although needing confirmation on a larger number of animals, the freezing extender used in the present work disrupted the mechanism of sperm hyaluronan binding prior to the freezing-thawing, suggesting a close relationship between this finding and lower fertility rates following artificial insemination with frozen-thawed semen.