Effect of Quercetin on Capacitation Status and Lipid Peroxidation of Stallion Spermatozoa

Lower fertility of preserved stallion semen may be caused by damage to the spermatozoa or premature capacitation during storage. We investigated the use of the flavonoid, quercetin, with a standard skim milk extender for storage of stallion spermatozoa to prevent premature capacitation and acrosome reaction and to reduce the damage to spermatozoa from lipid peroxidation. Several concentrations of quercetin (0.05, 0.1, 0.2, 0.3 mM) were mixed with skim milk-glucose extender, and the antioxidant effectiveness was assessed using xanthine–xanthine oxidase challenge for 21 h. The effect of quercetin on capacitation status of sperm was assessed during a 4 h incubation at 33°C, and a storage trial at 5°C for 6 days. In addition, the ability of sperm stored in quercetin extender to undergo capacitation and acrosome reaction was assessed using heparin and A23187. Lipid peroxidation in the sperm after challenge was inhibited by any concentration of quercetin in the medium, while 0.1 and 0.3 mM quercetin were most effective at preventing capacitation and acrosome reaction during a 33°C incubation. During storage at 5°C for 6 d, quercetin addition to the extender significantly reduced the proportion of sperm capacitation. Heparin had no effect on capacitation status in either extender, but A23187 increased the proportion of sperm stored in the quercetin extender undergoing capacitation and acrosome reaction. In conclusion, quercetin in the standard skim milk–glucose extender for equine semen during storage reduces lipid peroxidation of the sperm, maintains internal adenosine triphosphate (ATP) concentration, and prevents premature capacitation of sperm cells before insemination while still allowing the sperm to capacitate and acrosome react after insemination.