Zum Einfluss eines automatischen Melkverfahrens auf Milchmengenleistung und Milchinhaltsstoffe hochleistender DH-Kühe unter Berücksichtigung von Laktationsstadium und Eutergesundheit

Milk yield, parameters of udder health and other milk constituents of a high-yielding herd milked with an automatic system were surveyed in relation to lactation stage and udder health over a period of 13 months. Sampling was performed at 20 days and comprised a total of 7,068 pre-milk, foremilk and composite samples on quarter level, along with 1,802 cow composite samples, all originating from 47 animals. This study was intended to evaluate the influence of an automatic milking system (AMS; here: VMS® = Voluntary Milking System®) on the secretory activity of the bovine mammary gland, on inflammatory parameters (somatic cell count, NAGase activity, electrical conductivity, lactate) in different milk fractions, and on other selected milk constituents (fat, protein, lactose, urea). Udder health was categorized cytobacteriologically, according to DVG (German Veterinary Medical Society) recommendations. Doing so, a marked prevalence of Corynebacterium spp. was encountered. This prevalence even increased during the trial and led to a decrease of the herd’s udder health state. An interaction between this development and the milking system could not be fully denied, since pathogen dissemination due to unsatisfactory teat disinfection seemed feasible. In the same time, the amount of infections due to CNS decreased, and other pathogens were responsible for even less than 5 % of cases. Mean cell count averaged constantly on a very low level (xg < 60,000 cells/ml). The recorded data shows that, on average, 12.8 % of all 35,762 milkings performed during the trial phase were incomplete. By comparing two different periods it was seen that the percentage of incomplete milkings (ICM) varied markedly. Up to 50 % of all ICM could be traced back to merely 12 % of the cows suggesting that, in these animals, individual udder conformation or behaviour patterns led to the unsuitability for AMS. Apart from that, ICM were primarily caused by technical errors (especially problems in (re-)positioning the teat cups). In spite of the mean milk yield not being affected significantly, effects on the secretory activity became noticeable when the amount of cases surpassed 10 %. Therefore, it is recommended to control the problem by improving the positioning technique. As ICM during the sampling sessions were practically avoided by manual positioning of teat cups (a routine included in the sampling procedure), mean milking frequency during these days was lower (2.72 milkings/cow/day) than during the rest of the time where it amounted to 2.86 milkings/cow/day. This was due to the fact that cows with ICM regained immediate access to the milking facility in order to complete the milking. Lactation stage, milking interval and udder health influenced milk yield in descending order of importance. The effect produced by the interval was seen to be significant for both healthy and diseased quarters (p < 0.05). The secretion rate did not behave linearly in relation to the milking interval but decreased with increasing interval length of the last milking. On cow level and applying intervals of 6 - 8 h, 8 - 10 h, 10 - 12 h and 12 - 14 h, 89.9 %, 83.0 %, 75.6 % and 67.8 % of the milk yield obtained after intervals of 4 - 6 h were recorded, respectively. The yield-increasing potential could only be utilized at the beginning of lactation. Shifting between short and long intervals triggered individual, varying responses. A general tendency showed that cows in early lactation reacted more sensitively. Their mean secretion rate after a series of continuously long intervals was higher than after changing milking intervals. In comparison to quarters with a somatic cell count of < 50,000 cells/ml, secretion rate already dropped from 315 to 266 g/h/quarter when cell counts ranged between 50,000 and 100,000 cells/ml. Significant changes (p < 0.05) in the concentration of inflammatory parameters as well as other milk constituents (with the exception of urea) were also observed in quarters with that cell count range (50,000 - 100,000/ml), although they are considered “normally-secreting”. Somatic cell content and NAGase activity were significantly higher in foremilk than in composite samples (p < 0.001). When comparing quarter composite and cow composite samples, lactose and urea values were not affected by milk fraction, while slightly increased concentrations in cow composite samples were observed for the rest of the parameters. Significant differences could be established for the cell count only (p < 0.001). No statistic influence of the milking interval was found on lactate and urea concentrations. NAGase activity, electrical conductivity and protein content rose with increasing milking interval while fat and lactose levels fell. In composite milk the somatic cell count was significantly increased at milkings after < 6 h compared to intervals between 6 and 8 h (p < 0.05), but increased again after longer intervals. With correlation coefficients of 0.18, 0.19 and - 0.14 respectively, NAGase activity, electrical conductivity and fat content showed the greatest dependency on the milking interval. The milk composition of healthy quarters milked via AMS using milking intervals between 4 and 14 hours was found to be ranging within the physiological limits already established under conventional conditions, even despite the wide array of values displayed occasionally. However, when evaluating samples from AMS-milked farms, the influences studied in this paper might become superimposed on the results and may therefore lead to misinterpretation.