The major membrane nuclease MnuA degrades neutrophil extracellular traps induced by Mycoplasma bovis.

Mycoplasma bovis has been increasingly recognised worldwide as an economically important pathogen of cattle, causing a range of diseases, including pneumonia, mastitis, polyarthritis and otitis media. It is believed that M. bovis utilises a range of cell surface proteins, including nucleases, to evade the host immune response and survive. However, despite the importance of neutrophils in controlling pathogenic bacteria, the interaction between these cells and M. bovis is not well-characterised. In addition to phagocytosis, neutrophils combat pathogens through the release of neutrophil extracellular traps (NETs), which are composed of their nuclear and granular components, including DNA. Here we investigated the effect of the major membrane nuclease MnuA of M. bovis, which in vitro is responsible for the majority of the nuclease activity of M. bovis, on NET formation. We quantified NET formation by bovine neutrophils 4 h after stimulation with wild-type M. bovis, an mnuA mutant and a mnuA-pIRR45 complemented mnuA mutant. NETs were detected following stimulation of neutrophils with the mnuA mutant but not after exposure to either the wild-type or the mnuA-pIRR45 complemented mutant, and NETs were degraded in the presence of even low concentrations of wild type M. bovis. Surprisingly, there was no increase in levels of intracellular reactive oxygen species (ROS) production in neutrophils stimulated with M. bovis, even though these neutrophils produced NETs. These results clearly demonstrate that M. bovis can induce NET formation in bovine neutrophils, but that the major membrane nuclease MnuA is able to rapidly degrade NETs, and thus is likely to play a significant role in virulence. In addition, M. bovis appears to induce NETs even though ROS production seems to be suppressed.

The effects on claw health of supplement feeding grazing dairy cows on feed pads.

The effects of feeding and management systems on the health and welfare of grazing dairy cows were investigated by comparing the claw health of cows fed grain during milking and pasture silage in the paddock (Control), with cows fed a grain-based partial mixed ration (PMR) on a concrete feed pad. Cows were assessed on three occasions during lactation: (1) early lactation (20-81 days in milk [DIM]) before allocation to feeding treatments; (2) mid-lactation (97-158 DIM) immediately following an intensive feeding experiment, and (3) late lactation (173-243 DIM) several months after return to initial management groups. At the final examination, claw puncture resistance was measured. The results showed that for the most prevalent lesions (white line disease, paintbrush haemorrhage and traumatic bruising), there was no effect of feeding system or amount of supplement on the presence of the moderate to severe forms in early lactation, but cows were more likely to have a particular lesion at the second assessment if it was present in early lactation. Puncture resistance of the claw was not related to presence of a lesion for any of the most prevalent lesion types. It was concluded for this herd that for most indicators of claw health, there was no overall effect of different feeding systems (supplement fed during milking or on a feed pad) or amount of supplement.