Effect of Synergism Between Carboxylated Poly-l-Lysine and Glycerol on Freezability of Nili-Ravi Buffalo (Bubalus bubalis) Semen.

Carboxylated poly-l-lysine (CPLL), an ampholytic polymer, has remarkable cryoprotective properties. It was hypothesized that CPLL will reduce/replace glycerol in extender and improve the freezability of buffalo semen. The objective was to evaluate various combinations of CPLL and glycerol in extenders for any synergism toward cryosurvivability of Nili-Ravi buffalo sperm. Semen collected from four Nili-Ravi buffalo bulls (ejaculates = 40; replicates = 5) was diluted in tris-citric acid based extenders, Control: (0% CPLL +7% Glycerol); E1: (1% CPLL +6% Glycerol); E2: (2% CPLL +5% Glycerol); E3: (3% CPLL +4% Glycerol); E4: (4% CPLL +3% Glycerol); E5: (5% CPLL +2% Glycerol); E6: (6% CPLL +1% Glycerol), and E7: (7% CPLL +0% Glycerol), and cryopreserved using a programmable cell freezer. Percentages of post-thaw sperm motility, plasma membrane integrity, and acrosomal integrity were found to be higher (p < 0.05) in extenders E1, E2, E3, E4, and E5 compared to E6 and the control. Sperm livability (%; live/dead ratio) and viability (%; live sperm with intact acrosome) were higher (p < 0.05) in extender E4 compared to all the other extenders. Sperm DNA integrity was higher (p < 0.05) in extender E2, E3, E4, and E5 compared to control, E1, and E6 extenders. Sperm lipid peroxidation levels were lower (p < 0.05) in E3, E4, E5, and E6 compared to control, E1, E2, and E7 extenders. Total antioxidant capacity of seminal plasma was higher (p < 0.05) in extenders E5, E6, and E7 than control, E1, E2, E3, and E4 extenders. It is concluded that synergism between CPLL and glycerol (4% CPPL and 3% Glycerol) seems to improve the freezability of Nili-Ravi buffalo semen by reducing oxidative stress.