15 Bulletin UASVM, Veterinary Medicine 68(1)/2011 pISSN 1843-5270; eISSN 1843-5378 Amino Acid Concentration in Normal and Subclinical Mastitis Milk Sanda ANDREI 1 , Monica CULEA 2 , Sorana MATEI 1 , Adela PINTEA 1 , GROZA I.S. 1 1) University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Faculty of Veterinary Medicine, Str. Mănăştur no. 3-5, Cluj-Napoca, Romania 2) ”Babes-Bolyai” University, Str. M. Kogalniceanu no.1, Cluj -Napoca, Romania Email: sanda_m_andrei@yahoo.com Abstract. The aim of this study was the evaluation of amino acid concentration in milk collected from cows with sub clinical mastitis compared with healthy cows. A first step was the diagnosis of mastitis, using the method based on electrical conductivity and also the determination of milk somatic cells number. Next, in all milk samples, we determined the concentration of total amino acids and the variations that occur between different types (essential and non-essential amino acids). Total amino acid content increased significantly in mastitis milk, compared to normal (mean values were 619,82±76,02 g/ml for normal milk and 12073,06±5.564,14 g/ml for the subclinical mastitic milk). In mastitis milk samples is an increase in the percentage of lysine, tyrosine, leucine, isoleucine, valine, glycine and alanine. Simultaneously, there were decreases in percentages of glutamic acid, ornithine, aspartic acid, methionine, proline, serine and threonine. For phenylalanine, no significant changes were observed. Key words: amino acids, subclinical mastitis, milk INTRODUCTION Milk proteins are considered as having a high biological value, due to essential amino acid content. This occurs not only in sufficient quantities, but more, in an optimum ratio for vital activity of the body. Milk and dairy products are rich sources of protein. From technological point of view is very important to describe the amount of protein in milk as well as characterization of these proteins in terms of amino acid content, particularly essential amino acids [Andrei and Groza, 2010]. Mastitis in dairy cows are the most important diseases of the mammary gland, with economic implications, due to losses in milk production and the risk posed by consumption of infected milk to public health. All milk variety contains a certain level of somatic cells represented by polymorphonuclear cells (PMN), lymphocytes and macrophages. In bacterial infection and other inflammation processes affecting the mammary tissue, the number of somatic cell (SCC) in milk increases, especially the PMN level [Hamed et al., 2008]. Numerous studies indicate that changes in the number of somatic cells are related to changes in the composition of milk, due to injurious processes mammary cells, which reduces the synthesis of milk constituents in the gland. Another explanation is the change in membrane and interstitial spaces permeability, which increases the passage of the components of blood in milk [Groza, 2006; Petrovsky, 2006]. Milk from clinically and subclinically affected mastitis cows had very high increase in the activity of proteolytic enzymes. The main caseinolytic enzyme in milk, plasmin, is able to rapidly cleave caseins in polypeptide