No abstract

SummaryThe effect of a switch level of 200 or 400 g/min for automatic cluster removers on milking performance and udder health was measured with 71 first lactation cows in their first 36 weeks of lactation and with 64 older cows in their first 12 weeks of lactation. Early removal of the milking unit decreased machine-on time by 0·5 min, increased average milk flow rate slightly, improved teat condition significantly and reduced the change in teat end thickness during milking of first lactation cows. Early removal of the milking unit did not affect milk yield or composition, and the incidence and prevalence of subclinical mastitis were the same in the two groups. Fewer older cows developed clinical mastitis in the group switched at 400 g/min, but this was not significant. It is concluded that the milking unit can be detached at a milk flow rate of 400 instead of 200 g/min without having a negative influence on milk yield. Machine-on time is shortened and teat condition improved, and udder health does not seem to be affected.

We examined the physical and chemical changes in milk during early lactation, and how these changes were affected by leaving one quarter unmilked in either the first or second milking, with the purpose of discriminating between colostrum and normal milk. Milk samples were collected from each quarter of 17 cows during the first 5 d after calving and then after about 7 d and 14 d. Samples were analysed for somatic cell count (SCC), fat, protein, casein, lactose, IgG1, colour, plasmin, pH and coagulation properties. Large variations occurred in both chemical and physical properties throughout the study period. Within six milkings, the concentration of casein decreased by 60%, IgG1 by 94%, and lactose increased by 34%. At milking number 6, rennet coagulation time was lowest and curd firmness was highest. The pH increased from 6·4 to 6·7 over the period of the experiment, and the colour changed from yellow (reddish) to white. Coagulation properties and the pH fell within the range of normal milk after five milkings. Measurement of colour and density appeared to be a potential method for detection of milk unsuitable for the dairy factory. Effects of omitting one quarter in one milking differed between milk components, but seemed to be of little importance to the physical properties.

The influence of milkline vacuum, pulsator airline vacuum, and cluster weight on complete lactation milk yield performance, teat condition, and udder health were studied in 241 cows by using three separate factorial experiments. The first experiment had milkline vacuum set at 38 and 48 kPa, pulsator airline was vacuum was set at 0 and 8 kPa above milkline vacuum, and cluster weight was 1.6 and 2.3 kg. The second experiment had milkline vacuum set at 38 and 48 kPa and cluster weight was 1.6 and 2.3 kg. The third experiment had milkline vacuum set at 32 and 42 kPa and pulsator airline vacuum 0 and 8 kPa above milk line vacuum. The first two experiments were carried out with a high-level milking and the third with a low-level milking system. The average vacuums in the short milk tube during milking for low and high milkline vacuum in the high-level system were 26 and 33 kPa, and 30 and 39 kPa for the low-level milking system, respectively. Milking at low vacuum increased the machine-on time and frequency of liner slip, decreased milk flow rate, but had no influence on teat condition and udder health. The milk yield of high producing cows with long machine-on time was reduced by 5% when milked at a low vacuum. A higher pulsator airline vacuum than milkline vacuum had no influence on milking performance. The use of the light cluster reduced machine-on time. We recommend that mean vacuum in the short milk tube should not be lower than 32 kPa.