Supplementation of cauda epididymal plasma improves sperm characteristics following liquid preservation of ram semen at 3-5°C

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 mu M 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 mu m 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 mu m 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.