Influence of different liquid nitrogen levels on bull sperm cryostorage and its impact on sperm quality

The study aimed to compare the impact of liquid nitrogen (LN2) levels within the storage dewar on sperm quality and investigate the effects of the nitrogen level on the sperm straws stored at the top or bottom of the semen racks. A total of 48 straws from 8 different bulls were used. Analyses were performed at three different LN2 levels within the dewar (30, 15, and 7 cm), and at each level, two straws (one from the top and one from the bottom of the rack) from each bull were used. Analyses included assessing mitochondrial membrane potential (MMP), plasma and acrosomal membrane integrity (PMAI), and sperm kinematics using CASA. Neither the evaluated nitrogen levels nor the straw storage location in the top or bottom goblet of the rack affected sperm quality. There were no differences in total and progressive motility or MMP and PMAI. The results obtained in this study show that, as long as the internal temperature in the dewar is maintained at -194 °C or below, even at the lowest evaluated liquid nitrogen level, there is no loss of sperm quality, regardless of the storage location of the straw in the rack.