Conventional and positive pressure pulsation effects on bovine teats and on immunological components of different milk fractions

The physical forces applied during mechanical milking may be able to cause changes in the teat tissue, blood circulation and cell population, which could modify the local immune capacity. To assess the influence of machine milking on the teat tissue immune status, a cross-over study was undertaken in which the effects of a positive pressure milking system (POP) were compared with those of a conventional milking unit (CON). The results of the measurement at the teat end indicated significantly smaller diameters and significantly lower thickness values after milking by POP compared to CON. Overall, the PMN fraction in the teat secretion was not influenced by the milking systems applied, while a significant decrease of the macrophages proportion was observed for POP. This was probably a consequence of the reduction in the fluid volume in the teat end, as confirmed by the reduction in NAGase concentration during the POP phases. These data are the first in the literature indicating a direct relationship between machine milking and changes in differential cell counts with potential influence on the local cellular defence mechanisms. In this study the level of mechanical irritation was low after POP application and the effects on cells were therefore not mediated by an inflammatory reaction.