Influence of Equilibration Time and Bull-Specific Extender for Cryopreservation on Semen Quality and Fertility in German Holstein Friesian Bulls: A Controlled Field Trial

SIMPLE SUMMARY: Cattle sperm needs to be equilibrated to reduce damage during freezing. Equilibration is the time that the sperm spends in a freezing solution, the extender. Commonly, bull studs require 4 h equilibration time. However, this creates a high workload on the two to three days when bull sperm is collected during a week. We aimed to find the best equilibration time and extender, and to observe the effects on fertility in the field. We found that increasing the equilibration time from 4 h to 24 h improved sperm quality when using the extender Triladyl. The extenders Triladyl and OptiXcell yielded the best laboratory results at 24 h equilibration compared to the extender BioXcell. Field fertility did not differ among the three combinations of extender and equilibration time that we tested. Therefore, it is possible to change from 4 h to 24 h equilibration time while potentially improving laboratory sperm quality and without negative effects on fertility. ABSTRACT: Equilibration with an extender is necessary to allow cryopreservation of bovine sperm. The aim of trial 1 was to assess the effect of 24 h versus 4 h equilibration time with three different extenders on sperm quality and to select the preferred extender for each bull. The aim of trial 2 was to investigate the effect of using a 24 h equilibration time with a bull-specific extender on field fertility. For trial 1, three ejaculates each from eight Holstein Friesian breeding bulls were used as the split-sample, including two equilibration times (4 h and 24 h) and three extenders (BioXcell, Triladyl, and OptiXcell). For trial 2, from 5 to 10 ejaculates from the same bulls were collected and treated (split-sample) as BioXcell with 4 h equilibration and either Triladyl or OptiXcell, both with 24 h equilibration. A total of 11,059 straws were used for insemination of cows and heifers. For Triladyl, progressive sperm motility, acrosome defects, and plasma membrane and acrosome integrity improved with a 24 h compared to a 4 h equilibration time. Four bulls each were used with Triladyl and OptiXcell for trial 2. In trial 2, non-return rates did not differ among groups. Therefore, using a 24 h equilibration time might improve in vitro sperm parameters, depending on the extender used. Moreover, it would be possible to change from 4 h to 24 h equilibration time without impairing field fertility.