Comparison of plant- and egg yolk-based semen diluents on in vitro sperm kinematics and in vivo fertility of frozen-thawed bull semen

Diluents using components of plant origin have been developed as an alternative to animal based extenders for the dilution of bull semen, however, it is unclear if use of these diluents results in in vivo fertility rates similar to those that occur with use of traditional egg yolk-based diluents. The aim of this study was to assess the effect of semen diluent on 60-day non-return rate (NRR) following artificial insemination (AI) with frozen-thawed bull semen. The effect of semen dilution in one of three different commercial diluents (BullXcell - egg yolk-based, OptiXcell - plant-based or AndroMed - plant-based) on post-thaw total and progressive motility as well as kinematic parameters (Experiment 1) and field fertility (Experiment 2, n = 1,480 inseminations) was assessed. Semen stored in OptiXcell had greater post-thaw total and progressive motility than AndroMed (P < 0.05) but did not differ from BullXcell. Semen stored in BullXcell had a greater beat cross frequency and straight line velocity compared to semen stored in AndroMed (P < 0.05) but did not differ when compared with use of OptiXcell; while values for these variables when using OptiXcell and AndroMed did not differ from each other (P > 0.05). There was no difference in any other sperm kinematic parameters (P > 0.05). There was no effect of diluent on 60-day NRR (71.5%, 67.8% and 70.6% for BullXcell, OptiXcell and AndroMed, respectively). In conclusion, while diluent significantly affected post-thaw sperm motility and kinematics, no effect on 60-day NRR was observed. Given that OptiXcell and AndroMed are animal protein-free media these diluents may be a suitable alternative to BullXcell for the storage of frozen-thawed bull semen.