41 THE EFFECT OF AMBIENT TEMPERATURE ON SPERM MOTILITY DURING LIQUID STORAGE OF VENDA COCK SEMEN AND INDIVIDUAL DIFFERENCES IN SPERM CRYOTOLERANCE

Improving techniques for liquid storage of cock semen can increase the efficiency of AI programs in the poultry industry. The aims of the present study were (1) to compare storage of cock sperm for 24 h at 5 and 25°C and (2) to test the cryotolerance of sperm cell motility in individual Venda cocks. Semen was collected with the abdominal massage method, from 6 indigenous Venda cocks. Cocks were 26 weeks of age and were kept under the same conditions. After macroscopic analysis, semen was pooled and diluted (1:2) with Kobidil+ extender and divided into 3 equal parts. Part 1 was evaluated immediately (0 h), part 2 was stored at 5°C and part 3 was stored at 25°C and evaluated for sperm motility and velocity parameters at 4, 8, 12 and 24 h of storage. For cryopreservation, semen was diluted (1:2) with modified Kobidil+ extender supplemented with 8% of dimethyl sulfoxide. Individual ejaculates were equilibrated at 5°C for 4 h and then loaded into the programmable freezer. Then, semen straws were thawed at 5°C. Sperm motility and velocity parameters were evaluated using the Sperm Class Analyzer® system. Six replicates were done per trial. Data were analysed using the statistical programme GenStat®. Treatment means were separated using Fisher's protected t-test least significant difference (P < 0.05). Total sperm cell motility rate was 87.5% and decreased significantly during in vitro storage and was <31% after 24 h at 25°C. Semen samples stored at 5°C showed a total sperm cell motility rate of above 50% after 24 h. There was a slight linear decrease in the percentage of sperm with progressive motility and rapid velocity as the storage period increased, irrespective of the storage temperature. The rapid and medium motility percentages were higher in fresh semen and significantly decreased (P < 0.05) during the incubation period. There was variation in the total sperm cell motility of fresh and frozen semen among cocks. There was no significant difference in variation in non-progressive and medium percentage (P > 0.05) motility in diluted fresh or frozen sperm cells or in the percentage of sperm with rapid motility in thawed semen. There was variation in <25% of the cocks in total sperm motility rate. In summary, cryopreservation reduced sperm cell motility and velocity rates in all the cock semen donors. We found that cryotolerance of cock sperm does vary among males. Furthermore, the lower temperature 5°C was suitable for semen storage of Venda cocks. This temperature (5°C) could potentially improve methods of semen equilibration before cryopreservation. The study was supported by an Agricultural Research Council Parliamentary Grant, Department of Agriculture Forestry and Fisheries and National Research Foundation-GUN No RT21 and 24000 (NRF). The Germplasm Conservation & Reproduction Biotechnologies (GCRB) group is thanked for their support.