Bovine spermatozoa and Lactobacilli interactions: deterioration or improvement of the sperm vitality?

Bacteriospermia is a serious problem in animal production since bacteria may negatively affect sperm behavior. It is well known that various bacteria occur naturally in bovine semen; however, it should be noted that not all bacterial species need to pose a threat to male fertility. Lactobacilli are a natural part of vaginal secretions and present with probiotic effects. We were interested in how lactobacilli species L. buchneri, L. curvatus and L. hilgardii would affect sperm activity and oxidative profile. Ejaculates were obtained from 5 breeding bulls. To eliminate the effect of bacteria naturally present in the ejaculates, spermatozoa were washed out with Percoll® Plus density gradient and diluted in sperm Tyrode's albumin lactate medium. The suspensions were exposed to bacterial isolates at 0.5 McFarland turbidity, incubated at 37°C and evaluated after 15 and 30 min. Motility was assessed using the computer assisted sperm analysis, mitochondrial activity was determined by the colorimetric MTT assay, production of reactive oxygen species (ROS) was quantified luminometrically, and superoxide production was evaluated by the nitroblue-tetrazolium (NTB) assay. The data were processed using One-Way ANOVA and Dunnet's test. Following 30 min of co-culture, higher motility (P<0.05) was observed in case of L. curvatus. An increase in mitochondrial activity was observed in L. curvatus (P<0.001) and L. hilhgardii (P<0.01) after a 30 min incubation. Lower ROS production was recorded in the samples subjected to in L. curvatus and L. highardii (P<0.01) following 30 min of culture. Furthermore, reduced superoxide production was observed following 30 min in case of the samples co-incubated with L. curvatus (P<0.001) as well as L. hilghardii (P<0.001). Our results suggested that L. curvatus and L. hilgardii have beneficial effects on sperm motility, mitochondrial activity, and exhibit antioxidant properties during a short-term co-incubation. Although this topic requires further research, we may hypothesize that lactobacilli could have potential in bovine sperm processing techniques. This study was supported by the VEGA 1/0239/20 and KEGA 008SPU-4/2021 project.