Cholesterol-loaded-cyclodextrins improve the post-thaw quality of stallion sperm

An unacceptable proportion of stallion sperm do not survive the freeze-thaw process. The hypothesis of this study was that adding cholesterol to a stallion semen extender would stabilise the sperm membrane, resulting in an improved post-thaw semen quality in terms of increased sperm viability, membrane integrity and fluidity, and reduced oxidative stress. Semen was collected from three stallions and diluted in four extenders: TALP; TALP+0.75mg methyl-β-cyclodextrin-cholesterol (MβCD)/mL (MβCD_0.75); TALP+1.5mg MβCD-cholesterol/mL (MβCD_1.5); and Equipro. Following 15min incubation, samples were centrifuged and diluted to 100×10⁶sperm/mL, frozen in 0.5mL straws and stored in liquid nitrogen. Sperm from each treatment was assessed for progressive linear motility (PLM) and acceptable membrane integrity under hypotonic conditions on a phase contrast microscope at 1000× while viability, membrane fluidity and superoxide generation were assessed by flow cytometry. The MβCD_1.5 and MβCD_0.75 treatments had a greater proportion of viable sperm than the TALP treatment (P<0.01). There was no effect of treatment on PLM or membrane integrity. The MβCD_1.5 treatment had a greater proportion of viable sperm positive for membrane fluidity than the TALP treatment (P<0.05). The MβCD_1.5 and MβCD_0.75 treatments had a lesser proportion of viable sperm positive for superoxide generation than the TALP treatment (P<0.001). This study has demonstrated that adding cholesterol to stallion sperm prior to cryopreservation increases post-thaw viability, with these viable sperm being of better quality in terms of increased membrane fluidity and reduced superoxide generation.