Effects of thawing times and temperatures on frozen semen of Boran bulls in Uganda

Abstract

Artificial insemination (AI) is the key technology in livestock production and is critically important for the maintenance of genetic diversity (Niemann & Wrenzycki, 2018). However in Uganda AI has been adopted less than 10% despite the fact that it has been present for over 6 decades. This study aimed at evaluating the effect of different times and temperatures on overall motility, live-dead ratio and membrane integrity on frozen Boran bull semen kept at NAGRC and DB. The semen used was got from the National Animal Genetic Resource Center and Data Bank of Uganda. The semen straws used in this study were from the same batch collected and packed on the date of 20th Jan 2022. Using the archived data, the semen batch used in this study had the following parameters before cryopreservation, progressive and overall motility of 85%, motility at 4oC was 85% and motility after freezing was 75% and concentration was 1800 million/milliliter. For statistical analysis of the semen parameters, that is average mean and standard deviation values were used and the semen straws were grouped into 4 groups, A, B, C and D, each group consisting of 10 straws. 2 straws from each group were thawed at 30, 37, 45 and 60 seconds respectively. Overall motility was evaluated using a computerized semen analyzer (CASA) software, live-dead ratio was established using Eosin-Nigrosin staining technique and membrane integrity was evaluated using HOST solution as described by Correa et al. The effect of times and temperatures on semen parameters was tested by one-way ANOVA using STATA version 15. Thawing at 30oC for 5 seconds gave the poorest motility of 10%, from 20oC to 60oC, motility slightly improved but still was below the recommended 50%. Thawing at 37oC for 60 seconds gave the best motility of 70%, at 5 seconds, the motility was low at only 30%, from 10 seconds, 20 seconds and 35 seconds, motility was good with 61.67%, 63.33% and 66.67% respectively. At 45oC, motility was moderately good for all the thawing times of 5, 10, 20, 35, and 60 seconds giving 53.33%, 56.67%, 60%, 55% and 56.67% respectively. And at 60oC, motility was only moderately good at 5 and 10 seconds with a percentage of 53.33 and 56.67% respectively. The live-dead ratio for all the thawing temperatures was very good ranging between 96 to 99%. The membrane integrity for thawing temperature at 30, 37, 45oC was good ranging between 60 and 80%. At 60oC, membrane integrity declined as temperatures increased, 59.67% for 5 seconds, 46.33% for 10 seconds, 7.67% for 20 seconds, 5.67% for 35 seconds and only 1% for 60 seconds. In conclusion, temperature and time have a significant impact on the Boran bull semen. However, 37oC proved to be the best temperature for thawing semen aiming at the best results.