Bacterial Contamination of Liquid Nitrogen Tanks Used to Store Bull AI Doses: A Cross-Sectional Study

Extended bull sperm for artificial insemination is routinely cryopreserved and stored in liquid nitrogen (LN₂, -196°C) tanks to maintain semen quality for extended periods. Bacterial contamination impairs sperm quality; however, hygienic conditions of LN₂ tanks are monitored insufficiently. This study aimed to assess the hygienic situation in routinely used LN₂ tanks under field conditions. For this purpose, 141 LN₂ tanks from 19 AI centres were sampled to provide an overview of bacterial contamination prevalence. Additionally, antimicrobial susceptibility tests were performed for 13 commonly used antibiotics on all bacterial species isolated from three or more LN₂ tanks. Out of 141 LN₂ tanks, 81.7% were contaminated with one (44.3%), two (26.7%), three (9.2%), or four (1.5%) bacterial species, respectively. Overall, 25 bacterial genera were found, which yielded 49 different species. Results emphasise that contamination of LN₂ tanks used in bull AI is common. Systematic monitoring and the introduction of hygiene guidelines are, therefore, recommended.