Storage of fresh bovine semen in a diluent based on the ionic composition of cauda epididymal plasma

For artificial insemination (AI) in cattle, much lower insemination doses can be applied when fresh semen is used instead of frozen-thawed semen. However, a particular disadvantage of fresh semen is its limited shelf life. As bovine spermatozoa can be stored for several weeks in the cauda epididymis without negative effects on their fertilizing capacity, it is an interesting organ to serve as a model in order to prolong the shelf life of fresh semen. First, the storage capacity of a diluent [cauda epididymal plasma (CEP-1)] with the same ionic composition, pH and osmolarity as the bovine CEP was compared with a Tris diluent for extended preservation of fresh ejaculated bovine semen. Secondly, the ionic composition of the CEP-1 diluent was modified (CEP-2) and its storage capacity was compared with this of the CEP-1 and Tris diluent. Finally, the effect of addition of different polyols (sorbitol, glycerol, mannitol) and egg yolk concentrations (5, 10 and 20%) to the CEP-2 diluent was assessed. Sperm quality decreased rapidly in the CEP-1 diluent. The quality and especially progressive motility of spermatozoa stored in the CEP-2 diluent were better those in the CEP-1 and Tris diluent. No significant effects of different sugars or egg yolk concentrations on the quality of fresh bovine semen in the CEP-2 diluent were observed. In conclusion, the CEP-2 diluent with 10% egg yolk and 1 g/l sorbitol may be used for extended preservation of fresh bovine semen at 5 degrees C up to 6 days.