A comparison of semen diluents on the in vitro and in vivo fertility of liquid bull semen

The aim of this study was to assess the effect of semen diluent on calving rate (CR) following artificial insemination with liquid bull semen stored for up to 3 d postcollection. In experiment 1, the effect of storing liquid semen maintained at a constant ambient temperature in 1 of 7 different diluents [Caprogen (homemade), OptiXcell, BioXcell, BullXcell, INRA96, NutriXcell, or AndroMed (all commercially available)] on total and progressive motility was assessed on d 0, 1, 2, and 3 postcollection. In experiment 2, the field fertility of liquid semen diluted in Caprogen, BioXcell, or INRA96 and inseminated on d 1, 2, or 3 postcollection was assessed in comparison to frozen-thawed semen (total of n = 19,126 inseminations). In experiment 3, the effect of storage temperature fluctuations (4 and 18°C) on total and progressive motility following dilution in Caprogen, BioXcell, and INRA96 was assessed on d 0, 1, 2, and 3 postcollection. In experiment 1, semen stored in Caprogen, BioXcell, and INRA96 resulted in the highest total and progressive motility on d 1, 2, and 3 of storage compared with OptiXcell, BullXcell, NutriXcell, and AndroMed. In experiment 2, an effect of diluent on CR was found as semen diluted in BioXcell had a lower CR on d 1, 2, and 3 of storage (46.3, 35.4, and 34.0%, respectively) in comparison with Caprogen (55.8, 52.0, and 51.9%, respectively), INRA96 (55.0, 55.1, and 52.2%, respectively), and frozen-thawed semen (59.7%). Effects were found of parity, cow fertility sub-index, as well as the number of days in milk on CR. In experiment 3, when the storage temperature of diluted semen fluctuated between 4 and 18°C, to mimic what occurs in the field (nighttime vs. daytime), BioXcell had the lowest total and progressive motility in comparison to Caprogen and INRA96. In conclusion, diluent significantly affected sperm motility when stored for up to 3 d. Semen diluted in INRA96 resulted in a similar CR to semen diluted in Caprogen and to frozen-thawed semen, whereas that diluted in BioXcell resulted in a decreased CR. Consistent with this finding, semen diluted in BioXcell was less tolerant of temperature fluctuations than that stored in Caprogen or INRA96. Given that it can be used directly off the shelf, INRA96 may be a suitable alternative to Caprogen for the storage of liquid bull semen.