Mammalian spermatozoa remain immotile and metabolically inactive in the cauda epididymidis, thus maintaining fertility for several weeks. The aim of this study was to functionally characterise and evaluate the effect of cauda epididymal plasma (CEP) on liquid preservation of ram spermatozoa. Four experiments were conducted to investigate the effects of: (1) CEP and its fractions on sperm motility; (2) CEP (10%, 15%, 20% v/v) on liquid preservation of ram spermatozoa; (3) seminal plasma (SP; 20%, 30%, 50% v/v) on liquid-preserved spermatozoa; and (4) both CEP and post-storage SP treatment on sperm characteristics. Biochemical characterisation of ram CEP revealed high protein (30.9 mg mL−1), catalase (68.9 IU mL−1), alkaline phosphatase (17.5 IU mL−1) activities and total antioxidant capacity (1112 µM Trolox equivalent). Progressive motility of prewashed cauda spermatozoa was reduced (P < 0.05) by CEP or its protein-rich fraction compared with protein-free plasma or phosphate-buffered saline. After 48 h storage, total motility, rapid motility (average path velocity >75 µm s−1; 53.9%, 73.5% and 71.8% with 0, 15% and 20% CEP respectively) and straight line velocity (86.3, 102.1 and 102.4 µm s−1 with 0, 15% and 20% CEP respectively) were significantly (P < 0.05) higher in the CEP-treated groups than the control. Viability and acrosomal integrity were similar between groups; however, functional membrane integrity was higher (P < 0.05) in the 15% CEP-treated group. Treatment of liquid-preserved spermatozoa with either 20%, 30% or 50% SP improved (P < 0.05) rapid motility and kinematics at each time point of storage compared with control. In conclusion, liquid preservation of ram spermatozoa in the presence of 15% or 20% CEP and post-storage treatment with SP significantly improve sperm characteristics.

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Seminal plasma (SP) is known to induce motility and capacitation in spermatozoa curtailing their lifespan when preserved. Hence, this study was conducted to examine the effects of removal of SP from sperm surface prior to liquid preservation either by high dilution (1/15) or by washing and the poststorage treatment with SP (15% and 25%, v/v) on the quality attributes of liquid-preserved ram semen. Over the period of storage, the rapid motility (66.0% and 71.1% vs. 58.3%), straightness (87.1% and 82.1% vs. 79.4%), average path velocity (152.3 and 152.0 µm/s vs. 133.3 µm/s) and the straight-line velocity (131.3 and 127.8 µm/s vs. 108.5 µm/s) were significantly (p < 0.05) higher in both the high-dilution and wash groups as compared to the control (1/3 dilution). The functional membrane integrity (82.3% vs. 77.2%) and noncapacitated sperm count (65.0% vs. 58.7%) were also significantly (p < 0.05) higher in the high-dilution and wash groups, respectively, as compared to the control. The poststorage treatment of sperm with SP significantly (p < 0.05) increased the functional membrane integrity (70.1% vs. 53.8%) and most of the motility attributes as compared to the control (without SP). In conclusion, both the removal of SP prior to liquid preservation and poststorage treatment with SP significantly improved the quality attributes of ram spermatozoa.