Abstract
Fertility assessment of semen donor bulls used in Artificial Insemination programs is an important step in improving dairy industry in Sri Lanka. A study was conducted to evaluate the fertility of semen donor bulls using semen parameters and respective pregnancy rates. The semen donor bulls (n =21) in the Central Artificial Inseminations Station, Kundasale were selected for the study, and the hypo-osmotic swelling test was performed for both fresh and frozen semen of each bull. Data were analysed using statistical function of Excel software version 2010. Presence of high percentage of hypo-osmotic swelling positive spermatozoa in both fresh and post-thawed frozen semen indicated that all bulls studied were highly fertile. A total of 49255 AIs has been performed in four provinces with an overall pregnancy rate of 28.2%. The highest pregnancy rate of 57.6% was recorded in the Northern Province and the lowest pregnancy rate of 22.5% was recorded in the Central Province. The study revealed that there was no significant difference (p>0.05) in semen quality among individual bulls or among breeds. Al though the semen quality of the bulls was in the acceptable range, the pregnancy rate differed significantly (p<0.05) according to the area. In addition, the overall pregnancy rate was (28.2 %) below the acceptable level. Further studies are required to investigate factors associated with semen quality and the low pregnancy rates observed in some of the areas.