Epicatechin (EPC) is a flavonoid belonging to the family of catechins; it has been described as a powerful scavenger of a wide spectrum of reactive oxygen species (ROS) and a modulator of ex vivo sperm vitality. In this study, we assessed the potential protective abilities of EPC on cryopreserved bovine spermatozoa. We focused on conventional quality parameters, as well as the oxidative profile of spermatozoa alongside capacitation patterns, and expression profiles of proteins involved in the process of capacitation. Semen samples were cryopreserved in the presence of 25, 50 or 100 μmol/L EPC and compared to native semen (negative control) as well as ejaculates frozen in the absence of EPC (positive control). A dose-dependent improvement of conventional sperm quality parameters was observed following EPC administration, particularly in case of the sperm motility, membrane, acrosome and DNA integrity in comparison to the positive control. Experimental groups exposed to all EPC doses presented with a significantly lower proportion of capacitated spermatozoa as opposed to the positive control. While no significant effects of EPC were observed in cases of superoxide production, a significant decrease in the levels of hydrogen peroxide and hydroxyl radical were recorded particularly in the experimental groups supplemented with 50 and 100 μmol/L EPC. Western blot analysis revealed that supplementation of particularly 100 μmol/L EPC to the semen extender prevented the loss of the cation channel of sperm (CatSper) isoforms 1 and 2, sodium bicarbonate cotransporter (NBC) and protein kinase A (PKA), which play important roles in the process of sperm capacitation. In summary, we may hypothesize that EPC is particularly effective in the stabilization of the sperm membrane during the freeze–thaw process through its ability to quench ROS involved in damage to the membrane lipids and to prevent the loss of membrane channels crucial to initiate the process of sperm capacitation. These attributes of EPC provide an additional layer of protection to spermatozoa exposed to low temperatures, which may be translated into a higher post-thaw structural integrity and functional activity of male gametes.

This study examined the effects of three selected doses of kaempferol (KAE; 12.5, 25 or 50 μM) on bovine sperm motility and oxidative profile directly related to cold storage. We also elucidated the effect of KAE on the expression profiles of heat shock proteins (HSPs) 70 and 90 as well as the pro-apoptotic BCL2-associated X (BAX) protein and the anti-apoptotic B-cell lymphoma 2 (Bcl-2) protein. Frozen samples supplemented with KAE were compared with a native control (fresh spermatozoa) and a cryopreserved control, frozen in the absence of KAE. Our results demonstrate that the administration of all KAE doses led to a higher degree of sperm motility (p < 0.05) when compared with the cryopreserved control. The highest levels of protection of sperm DNA (p < 0.05), lipids (p < 0.05) and proteins (p < 0.05) were detected in samples exposed to 25 μM KAE when compared with samples frozen without KAE. Administration of 25 μM KAE led to a significant increase in HSP70 and HSP90 (p < 0.05) when compared with the unsupplemented frozen control. No significant differences were observed in the expression patterns of BAX; however, a significant up-regulation of Bcl-2 protein was observed in the frozen samples enriched with 25 μM KAE when compared with the cryopreserved control (p < 0.05). In summary, we may consider KAE as an effective agent in stabilizing the sperm membranes by preventing reactive oxygen species (ROS) overproduction in the mitochondria and subsequent oxidative damage to molecules critical for a proper sperm architecture and function. These protective properties of KAE may lead to higher post-thaw sperm activity and viability.

Bacterial contamination of semen is an important factor connected to the health status of bulls that may significantly affect semen quality for artificial insemination. Moreover, some important bovine diseases may be transmitted through semen. Up to now, only a very limited number of complex studies describing the semen microbiome of bulls have been published, as many bacteria are hard to cultivate using traditional techniques. The 16S rRNA high-throughput sequencing strategy allows for the reliable identification of bacterial profiles of bovine semen together with the detection of noncultivable bacterial species. Fresh samples from Holstein Friesian breeding bulls (n = 55) were examined for the natural variability in the present bacteria. Semen doses were selected randomly from Slovak Biological Services in Nitra, Slovak Republic. The most predominant phyla within the whole dataset were Firmicutes (31%), Proteobacteria (22%), Fusobacteria (18%), Actinobacteria (13%) and Bacteroidetes (12%). Samples of semen were divided into two separate clusters according to their microbiome compositions using a cording partition around a medoids analysis. Microbiomes of the first cluster (CL1) of samples (n = 20) were based on Actinobacteria (CL1 average = 25%; CL = 28%) and Firmicutes (CL1 = 38%; CL2 = 27%), while the second cluster (CL2; n = 35) contained samples characterized by a high prevalence of Fusobacteria (CL1 = 4%; CL2 = 26%). Some important indicator microbial groups were differentially distributed between the clusters.