Effects of season and single layer centrifugation on bull sperm quality in Thailand.

Objective: The aim of study was to investigate the effects of season and single layer centrifugation (SLC) before cryopreservation on post-thaw bull sperm quality in Thailand.

Methods: Semen was collected from 6 bulls (Bos indicus) in summer, rainy season and winter 2014 through 2016. Semen characteristics, sperm morphology, sperm kinematics, viability, chromatin structure and mitochondrial membrane were evaluated. Meteorological data were available from the local meteorological station.

Results: Season had an effect on semen characteristics in the raw ejaculate, with higher proportions of normal spermatozoa and lower abnormalities in winter than in the other two seasons. Sperm kinematics, viability, DNA fragmentation index, and mitochondrial membrane potential were not different between seasons. Sperm samples selected by SLC had greater normal morphology and a lower proportion with bent tails than controls and higher values of progressive motility (PRO), beat cross frequency, linearity, straightness, wobble (WOB), and lower values of slow motility, velocity average path (VAP), velocity curved line, and amplitude of lateral head displacement than controls. In addition, SLCselection had a favorable effect on PRO, VAP, and WOB that differed among seasons.

Conclusion: Our results suggested that these bulls were well adapted to their location, with season having an effect on sperm morphology. Moreover, SLC could be used prior to cryopreservation, regardless of season, to enhance normal morphology and kinematics of bull sperm samples without adversely affecting other parameters of sperm quality. However, there was considerable variation among bulls in DNA fragmentation index, mitochondrial membrane potential and sperm viability. In addition, SLC had a positive effect on sperm morphology and sperm kinematics, which could be expected to influence fertility.