Our objective was to determine effects of melatonin or L-arginine on quality of frozen-thawed sperm from heat-stressed (HS) rams. Ten Dorset rams were randomly allocated to either scrotal neck insulation for 3.5 d or whole-body heating (28 °C and 30-34% RH for 8 h/d for 4 consecutive days). Semen was collected before HS then once weekly for 1-5 wk, extended (Steridyl CSS One Step ®), and divided into 5 aliquots: control (no additive) or 0.5- or 1-mM of melatonin or L-arginine. For total and progressive motility (CASA), there were effects of group (P = 0.023 and P = 0.008, respectively); for morphological abnormalities (eosin-nigrosin), effects of group (P = 0.01) and a group*week interaction (P = 0.03); and for acrosome integrity (FITC-PSA), effects of group (P = 0.046) and week (P = 0.001). All 4 treatments improved motility (~5-10% points), whereas 1 mM of either compound optimized abnormalities and acrosomal integrity (~7% and 12% points, respectively). For superoxide dismutase and catalase, there were effects of week (P = 0.01 and P = 0.045, respectively), with 1 mM of either additive yielding best results. For DNA fragmentation index (DFI%), there was an effect of week (P = 0.01), and a group*week interaction (P = 0.05), with all 4 treatments reducing DFI%. For total ROS%, there was an effect of week (P = 0.044) and a group*week interaction (P = 0.037), with 1 mM melatonin or L-arginine being best. The hypothesis that melatonin or L-arginine improve quality of frozen-thawed sperm from HS rams was supported; 1 mM of either gave best results, except 0.5 mM minimized DFI%.
Keywords: Antioxidants; Heat stress; L-arginine; N-acetyl-5-methoxytryptamine; ROS; Sheep; Spermatozoa.
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