Effect of melatonin in different extenders on the quality of frozen semen of goats

The objective of this study was to investigate the effect of melatonin supplement in different extenders on the quality of cryopreserved goat semen. Six semen pools were cryopreserved in skim milk (SM – Experiment 1) or tris-egg yolk (TEY – Experiment 2) based extenders supplemented with melatonin (0, 0.5, 1, 2 and 4 mM). After thawing, the kinetic sperm parameters [total motility (TM), progressive motility (PM), curvilinear velocity (VCL), straight-line velocity (VSL), linearity (LIN), straightness (STR), wobble (WOB)] and viability parameters [plasma and acrosomal membrane integrity (iMPA), high mitochondrial membrane potential (hPMM) and intracellular ROS production (iROS)] were observed at time 0 h and after 2 h of incubation (37 °C). In the experiment I, only for the hMMP variable (p < 0.05), a melatonin vs time interaction was observed. Was noted a negatively influenced in the variables over the incubation period, except for the STR, iMPA, hMMP and iROS parameters. The treatment with melatonin had different effects in the variables VCL, VSL, WOB, hPMM, and iROS, however, in the variables TM, PM, LIN, STR and iMPA there was no significant difference regarding the different melatonin concentrations. In the experiment II, no interaction was observed, melatonin vs time, for the analyzed variables. Was noted a negatively influenced (p < 0.05) in all variables throughout the incubation period, with the exception of the STR, iMPA and hMMP parameters. The treatment with melatonin showed different effects in the variables TM, PM, VSL, LIN, STR, WOB, iMPA, hPMM and iROS, however, in the variable VCL there was no significant difference regarding the different concentrations of melatonin. In conclusion, melatonin does not improve the post-thawing quality of goat semen cryopreserved in SM or TEY based extenders and may be deleterious when supplemented at concentration of 4 mM.