Low-density lipoproteins, resveratrol and quercetin as alternative additives to improve boar semen cooling

Low-density lipoproteins (LDL), quercetin (Q) and resveratrol (R) have been used for sperm preservation to improve sperm quality in different species. To evaluate the effects of LDL, Q and R during the cooling of boar semen. Fifteen boar semen samples were diluted in a BTS extender supplemented with the treatments: LDL at 6%, Q at 10 μM (Q10), 30 μM (Q30) and 50 μM (Q50), or R at 10 μM (R10), 30 μM (R30) and 50 μM. A control without supplementation was included. The semen was stored by cooling at 16°C for 96 h. Every 24 h, sperm motility and kinetics were evaluated using a computer-assisted sperm analyzer (IVOS). At 24 and 96 h of cooling, functional membrane integrity and mitochondrial membrane potential (ΔΨM) of sperm were evaluated by the hypoosmotic swelling test (HOST) an flow cytometry with JC-1 probe, respectively, LDL improved progressive motility of sperm during cooling. Likewise, LDL increased average path velocity (VAP) and straight-line velocity (VSL) and/or curvilinear velocity (VCL) during the first 48 h of cooling. The use of Q between 10 and 30 μM caused a reduction in total motility, progressive motility and amplitude of the lateral head displacement during the entire cooling period, as well as a decrease in VAP, VSL and VCL at 96 h of cooling. LDL, Q10, Q30 and Q50 modulated mitochondrial activity by reducing high-ΔΨM sperm at 0 and 96 h of cooling. During the cooling of the boar semen prior to artificial insemination, the parameters of sperm quality that could influence fertility decrease; however, the inclusion of antioxidants and additives that protect the plasma membrane, such as LDL, could mitigate the damaging effects on spermatozoa. It is concluded that LDL can improve the motility and kinetics of boar semen during cooling while it could modulating the sperm's mitochondrial activity. On the contrary, Q could alter the motility and kinetics of boar sperm during the cooling period.