Impact of holding and equilibration time on post-thaw quality of shipped boar semen

Cryopreservation of boar semen is of growing interest for breeding companies. Overnight-shipping of pre-diluted ejaculates to specialized laboratories offers a practicable method, but requires fine-tuned protocols. In this study, the impact of holding post shipping at 17 °C for 2 or 24 h (n = 10 samples) and of equilibration in lactose-egg yolk extender without glycerol at 5 °C for 2, 4, 24 or 48 h (n = 11 samples) before freezing was investigated. Sperm-rich fractions of ejaculates from 21 mature Pietrain boars were collected at a single boar stud. After pre-dilution (1 + 1, v:v) with Beltsville thawing solution, samples were sent to the laboratory. Temperature profiles during transport and initial equilibration time were recorded. Semen quality post-thaw (PT) was evaluated using CASA and flow cytometry. Holding of 2 h after shipping resulted in higher sperm motility (P = 0.013) and beat cross frequency (BCF; P = 0.047) compared to 24 h. Differences between both groups vanished with prolonged incubation at 38 °C PT. Equilibration at 5 °C for 4 h yielded the highest motility and BCF, whereas the equilibration for 48 h impaired sperm motility. Membrane integrity, mitochondrial activity and DNA fragmentation index were not affected by any protocol modification. In conclusion, processing of pre-diluted boar semen shipped overnight within 2 h after arrival at the laboratory is preferred to 24 h of additional holding at 17 °C. Extending the equilibration period in lactose-egg yolk extender without glycerol at 5 °C from 2 h to 4 h before freezing is recommended.