The composition and quality of the raw milk is essential for the dairy industry and since only healthy cows produce milk of high quality, it is important with prospering cows. The most important and common disease among dairy cows is mastitis (inflammation of the udder). Mastitis is not only an animal welfare problem, but also results in impaired milk quality, reduced product yield, higher production costs and consequently a higher price for the consumer. The most common way to detect subclinical mastitis is by measuring the somatic cell count (SCC). The SCC is also an important parameter in milk payment systems, highly affecting the price to the producer. Since SCC is influenced by other factors than mastitis, e.g. lactation number, stage of lactation, stress etc., there is a need for new biomarkers for detection of subclinical mastitis as well as for raw milk quality. The aim of this thesis was to obtain further knowledge about the occurrence of the two major acute phase proteins (APP) in bovine milk, haptoglobin (Hp) and serum amyloid A (SAA), and to evaluate their potential as biomarkers for raw milk quality. For the first time, a method for analysis of Hp using an optical biosensor based on surface plasmon resonance (SPR) technology was developed. The method is fully automated with no need for sample preparation before analysis and each sample requires approximately 8 minutes. The occurrence of Hp and SAA in quarter, cow composite and bulk tank milk samples were investigated and the results showed that APP could be detected in all types of samples. In general, detectable levels of APP in milk were related to high SCC, probably originating from cows with subclinical mastitis. In general, samples containing APP had lower casein content, casein number (casein in relation to total protein) and lactose but also increased whey protein content or increased proteolysis. Hp and SAA were suggested to be useful biomarkers for milk quality, especially the protein quality. To our knowledge, this thesis is the first describing Hp and SAA as potential biomarkers for raw milk quality
