Förändras mjölkens proteinsammansättning i separata juverdelar i samband med höga celltal (SCC)?

Sammanfattning: Today the milk production per cow is increasing but the milk delivered by the Swedish farmer contains less amounts of fat and protein than earlier. The contents have decreased since 1993. In average the milk contain 4,2 percent fat and 3,4 percent protein. Earlier the fat content in milk was important. Nowadays the dairy's attention has turned to the milk's valuable proteins, principally the caseins, which have a considerable nutritional value and are important for several dairy products like cheese and yoghurt. An inflammation in the udder which injuries the udder tissue is called mastitis. Mastitis is a big problem among dairy cows. The immune system become activated when the cow gets mastitis which cause an increased somatic cell count in the milk and also changes in the milk composition. Mastits cause economical losses for the farmer, health problem for the cow and also problem for the dairy industry. Knowledge about different factors affecting the composition of the milk is therefore very important. The purpose of this study was mainly to investigate how the protein composition in milk was affected in connection with an increased somatic cell count (SCC). Except the protein composition even parameters like fat, lactose and milk yield have been studied. Compared to many other investigations this study was based on milk samples from each separate udder quarter. During a subclinical mastitis, when milk is not visually affected, is it especially important to collect samples from each quarter to avoid the dilution from the other healthy quarters. The study was conducted on Kungsängen research station at the Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala. The cows participating in the study were from the ordinary research stock. 24 cows participated in the study, 12 of these participated twice. 18 of the 24 cows were milked in an AMS (automatic milking system) while the rest of the cows were in conventional stables. 140 quarter milk samples were collected at seven occasions. To get a rough estimation about the cell count in the milk CMT (California Mastitis Test) was used, but all samples have also been analysed with electronic fluorescensbased cellcounting to get a more precise value of the cell count in the milk. This information was then used to decide which quarter that had an increased somatic cell count compared to the opposite quarter. To precipitate the casein the rennet method was used. Both the milk and the serum protein have then been analysed on the FTIR (Fourier Transform Infrared Spectroscopy) to get values for the fat- lactose- and protein content. To decide the casein content an indirect method has been used. The difference between the protein content in whole milk and in the protein content in the serum protein fraction have been calculated to get a value for the casein content in the milk. Most of the cows participating in this study had a very good udder health. Despite a low somatic cell count it was possible to detect several changes in the composition when a quarter had an increased SCC. The results from this study revealed that casein, casein number (casein: total protein), milk yield and lactose decrease significant with an increase in SCC. The whey protein increased significant. The fat content and the total protein content had some tendency to increase with an increased SCC, but these results were not significant. The amount of milk decreased with 23-24 %, lactose decreased with 4-5 % while the serum protein increased with 7-8 %. The casein number decreased with 2,5 % in a quarter with an increased SCC. Maybe 2.5 % sound negligble but because the casein number is a quotient between the casein content / total protein content such a decrease can have a considerable effect for the cheese making industry.