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 co uld modify the local immune capacity. To assess the influence of machine mi lking on the teat tissue immune status, a cross-over study was undertaken i n which the effects of a positive pressure milking system (POP) were compar ed with those of a conventional milking unit (CON). The results of the meas urement at the teat end indicated significantly smaller diameters and signi ficantly lower thickness values after milking by POP compared to CON. Overa ll, the PMN fraction in the teat secretion was not influenced by the milkin g systems applied, while a significant decrease of the macrophages proporti on was observed for POP. This was probably a consequence of the reduction i n 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 liter ature 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 lo w after POP application and the effects on cells were therefore not mediate d by an inflammatory reaction.