In our study, the mean values of 77.65±1.18% progressive forward motility, 58.40±1.43% functional membrane integrity, 58.50±1.12% viable cells and 65.05±1.63% acrosome intact sperm cells were recorded in the fresh semen samples of Black Bengal bucks immediately after dilution with semen extender. The mean values of the
in vitro sperm characters in post thawed semen following supplementation with L-cysteine as antioxidant @ 0 mM (control), 1 mM (CT
1 group), 2 mM (CT
2 group) are presented in Table 1.
Supplementation of L cysteine did not have any significant effect on the post thaw sperm motility and functional membrane integrity during cryopreservation of buck semen. Similar to current observation,
Tuncer et al., (2010) found that the addition of 10 mM cysteine did not exhibit significant cryo-protective effect on the
in vitro sperm parameters such as post-thaw motility and morphology. In contrary,
Ogretmen et al., (2015) reported that supplementation of cysteine @ 20 mM in the media yielded significantly higher post thaw motility (76.00±1.00%), fertilization rates (97.00±1.73%), hatching rates and decreased DNA damage during cryopreservation of semen in common carp (
Cyprinus carpio). Inclusion of 5 and 7.5mM cysteine in semen extender significantly (p<0.05) increased post thaw sperm motility and plasma membrane integrity with significant reduction in intracellular ROS when compared with control groups during cryopreservation of buffalo bull semen was reported by
Topraggaleh et al., (2014). Dolti et al., (2016) observed the post-thawed sperm motility was significantly higher in the extender added with 4mM cysteine and 50mM trehalose during cryopreservation of ram semen. Further, they reported that the spermatozoa motility decreased gradually in diluents containing cysteine and trehalose compared to control group.
Ansari et al., (2016) reported that the percentage of sperm cells with intact plasma membrane was higher in extender supplemented with 0.5 mM and 1.0 mM cysteine than the untreated control during cryopreservation of buffalo bull semen.
El-Sheshtawy et al. (2008) also reported a significantly higher percentage of sperm with intact plasma membrane after freeze-thawing with extender included with cysteine (5 mM) in Egyptian buffalo semen. Similarly, higher percentage of sperm cells with functional plasma membrane was observed in bull
(Sariozkan et al., 2009) and ram
(Uysal and Bucak, 2007) semen frozen-thawed in semen extender added with 2.0 mM and 5.0 mM cysteine. The overall mean values of viable sperm cells observed were 37.65±1.65, 39.45±1.66 and 39.60±1.80% in control, CT
1 with 1 mM L-cysteine and CT
2 group supplemented with 2 mM L-cysteine, respectively. In the present study, supplementation of L-cysteine @ 1 and 2 mM resulted in a non-significant improvement in the percentage of viable sperm cells in post thawed buck semen.
Ansari et al., (2016) attained significantly higher viable sperm cells in samples cryopreserved in tris-citric acid extender containing cysteine 0.5 mM and 1.0 mM compared with the control in buffalo bull semen. Similarly,
Bucak et al., (2008) also reported improvement in % of viable sperm cells after addition of 5.0mM cysteine in tris citric acid extender in ovine semen.
Dolti et al., (2016) also reported that the extender containing of cysteine and trehalose had a significant (p<0.05) effect on sperm viability during preservation of ram semen. The overall mean values of acrosome intact sperm cells were, 52.35±4.32, 53.00±4.23 and 55.45±4.55% in control, CT
1 and CT
2 group, respectively. Non-significant difference was observed in mean acrosome intact sperm cells of the control and CT
1 groups and between the treatment groups but CT
2 group had significantly (p<0.05) more acrosome intact cells than the control group. Acrosome membrane integrity is essential for the sperm cells to undergo capacitation, acrosomal reaction and finally fertilization
(Tartaglionea and Ritta, 2004). In the present study, buck semen samples supplemented with 2mM L-cysteine had significantly more acrosome intact sperm cells than the untreated control group. Akin to this observation,
Ansari et al., (2011 and 2016) recorded higher intact acrosome percentage in cryopreserved buffalo bull sperm due to addition of cysteine 1.0mM. Further,
Iqbal et al., (2016) also observed that post-thaw acrosome integrity were higher (p<0.05) with the addition of 2.0 mM L-cysteine in Nili-Ravi buffalo bull semen freezing. The mean values of MDA level in post thawed semen of Black Bengal buck were 2.384±0.12, 1.625±0.25 and 0.885±0.30 µmol/ml in control group without L-cysteine supplementation, CT
1 group with 1 mM L-cysteine and CT
2 group with 2mM L-cysteine respectively. Significant difference was observed between control and treatment groups and between treatment groups (p<0.01; p<0.05) in the mean concentration of lipid peroxide compound MDA. In this study, supplementation of L-cysteine @ 1 and 2 mM to the semen extender helped in controlling the development of lipid peroxide compound MDA during freezing of buck semen. Cysteine is a sulphur-containing amino acid, naturally found in seminal plasma and sperm nucleic acid, that acts as an antioxidant directly and/or indirectly through intracellular antioxidants that protect from ROS-mediated deleterious effects
(Perumal et al., 2011; Topraggaleh et al., 2014). In contrary to the present findings,
Tuncer et al., (2010) found that addition of 10 mM cysteine resulted in the highest level (4.99±0.44 nmol/mL) of MDA (P<0.001) when compared to the control (1.44±0.08). Similarly,
Sariozkan et al., (2009) also reported that supplementation of cysteine @ 2 mM to semen extender for freezing of bull semen did not show effectiveness on the elimination of MDA formation when compared to controls. These contradictory results may be due to the differences of semen extender composition, animal species and cysteine concentration used in the study. The overall mean values of superoxide dismutase activity observed were 0.381±0.031, 0.223±0.01 and 0.115±0.004 (U/mg of protein) in control, CT
1 and CT
2 group, respectively. Significant difference was observed between control and treatment groups and between treatment groups (p<0.01; p<0.05). Similar to the current observation,
Bucak et al., (2009) also reported that supplementation of the antioxidant cysteamine decreased SOD activity when compared to the controls (p<0.001) post freeze thawing of Angora goat semen.
Coyan et al., (2011) also found that the supplementation of cysteine did not significantly affect activities of SOD and GPx in Merino ram semen.