Effects of solid storage of sheep spermatozoa at 15 °C on their survival and penetrating capacity

This study was designed to evaluate the possible benefits of adding gelatin to a standard milk extender, for solid storage of sheep semen at 15 °C. Solid storage was assessed in terms of effects on sperm motility and membrane integrity up to 2 days (Study 1), and on in vitro penetration capacity after storage for 24 h (Study 2). In both studies, semen was diluted in CONTROL (standard milk extender) and GEL (1.5 g gelatin/100 ml extender) diluents to a final concentration of 400 × 106 sperm/ml. In Study 1, semen samples were stored at 15 °C, and sperm quality variables analyzed after 2, 24 and 48 h of storage. Motility and viability values were significantly lowered using the liquid compared to the gel extender for all storage periods, except for motility after 2 h of storage, whose values were similar. After 2 h of incubation at 37 °C, motile cell percentages and membrane integrity were significantly lower in the CONTROL group than in the GEL group for all storage periods. In Study 2, in vitro matured lamb oocytes were randomly divided into three groups and fertilized with CONTROL diluted semen stored for 2 h or 24 h, or with GEL diluted semen stored for 24 h. After co-incubation, oocytes were evaluated for signs of penetration. Storage of semen in the GEL diluent for 24 h gave rise to increased in vitro fertilization rates in comparison with the CONTROL diluent. Our findings indicate that the solid storage at 15 °C of ram spermatozoa by adding gelatin to the extender leads to improved survival and in vitro penetrating ability over the use of the normal liquid extender. A solid diluent could thus be a useful option for the preservation of fresh ovine semen for extended periods.