Mjölkningsfrekvensens påverkan på mjölkproteinets sammansättning och kvalitet

Sammanfattning: In modern dairy production the milking frequency is increased in some herds due to introducing of automatic milking systems or the farmers decision to milk high producing dairy cows more than two times a day. With more frequent milkings the milk yield increases while the content of fat and protein decreases. However, how the composition of protein is influenced is not fully evaluated. The purpose of this study was therefore to see if a higher milking frequency had any impact on the milk production and especially on the protein composition. This study was conducted as a half udder experiment. One side of the udder was milked two times and the other side was milked four times. The study was divided into two periods with five days in each. The first period both sides were milked two times and the second period one half of the udder was milked two times and the other was milked four times. There was a higher yield in the udder half milked four times in period two. For the milk components fat and lactose there were no significant effect due to treatment in period two. Protein yield in fresh milk increased but protein concentration decreased, in the side milked four times, compared to the side milked two times. The casein concentration had a significant lower value for the evening milking in both periods. For whey samples, the value was significantly lower in the evening milking in period one. In period two the values were significantly lower in both morning and evening milking on the side that was milked four times a day. Plasminogen showed only significant lower value on morning milking on the side milked four times in period two. The values for plasmin activity was significant lower at both morning and evening milking, for the side milked four times in period two. The change in proteolysis was not significant for the side milked four times in the second period. The value for sodium on the more frequent milked side in period two was significantly lower. For potassium, the values in period two was significantly higher for the more frequent milked side. The urea content in the milk was not significantly affected by the treatment in period two. In conclusion minor effects on protein content due to frequent milking were observed, while plasmin activity decreased. Further studies needed to evaluate if these findings are of importance in a long term perspective.