Evaluating of the effect of selected semen extenders on Ankole Longhorn bull semen under selected storage conditions

Abstract

The use of high-quality semen for breed improvement and conservation has prompted extensive research to develop new extenders for preserving semen of different livestock breeds. Ankole longhorn cattle is a culturally important breed of indigenous cattle in Uganda which is threatened by indiscriminate crossbreeding and needs to be conserved. The current study evaluated the effect of three locally formulated extenders on motility, viability, and acrosome reactivity of Ankole longhorn cattle semen using the computer assisted semen analyzer (CASA). Semen was collected from mature Ankole cattle bulls with average age of 4±0.5 years using an electroejaculator and subjected to macroscopic examination. Semen samples were then microscopically examined for mass motility, and then evaluated objectively using the CASA for motility, viability, and acrosome reactivity. After evaluation, each semen ejaculate was split into four equal parts and diluted with the four different extenders: coconut water-, egg yolk-, and soybean-based, and OptiXcell (control) extenders. The extended ejaculates were then packed into the French mini straws split into three. One part was kept at room temperature (25℃), another in a fridge (4℃) and then the other stored in liquid nitrogen (-196℃). Semen from each treatment was evaluated using the CASA. The mean ejaculate volume and pH were 7.32 ±0.13 and 6.53±0.09, respectively, within the normal range for bovine semen, and the semen colour was creamy-white. The mean mass motility of semen before extension was 84.63 ± 1.08%. Post extension, the highest motility was observed at 40C and the lowest was observed at 250C. At all temperatures, semen diluted in the control extender (OptiXcell) had the highest motility whereas semen diluted in coconut water-based extender had the lowest motility, but there were no significant differences in motility between the alternative extenders. In addition, whereas there were no significant differences in the percentage of abnormal spermatozoa across all temperatures when semen was preserved with OptiXcell, significant variations (p ˂ 0.02) were observed with all the alternative extenders. Nonetheless, no significant differences (p = 0.24) were observed in the percentage acrosome reactivity in all extenders at the different temperatures. These results highlight the feasibility of using fresh semen (40C) for field insemination within three days. They also indicate that OptiXcell is a far superior extender in preserving semen motility and viability. However, because commercial extenders are expensive, need may arise for them to be substituted, in which case the current results demonstrated that any of the locally formulated extenders may be used. Furthermore, if the sanitary concerns surrounding egg yolk-based extenders are bothersome, coconut water- and soybean milk-based extenders can be conveniently used as substitutes.