RAW MILK QUALITY IN THE DAIRY INDUSTRY: COMPOSITIONAL CHANGES CORRELATED WITH SOMATIC CELL COUNTS

Abstract Text: The aim of this study was to evaluate the seasonal correlation of somatic cell count (SCC) and composition of raw milk. A total of 287,000 samples of raw milk were analyzed during twelve consecutive months by the UFMG Milk Quality Laboratory (UFMG/Veterinary School; LabUFMG) for composition and SCC. The data were analyzed using descriptive statistics, according to the months of production and SCC ranges: Range 1: SCC ≤ 200,000 cells/mL; 2: SCC from 201,000 to 400,000 cells/ml; 3: SCC from 401,000 to 750,000 cells/ml, and 4: SCC> 750,000 cells/mL. The least significant difference between treatments was evaluated using Tukey’s test, with significance level of 5% in a randomized complete block design. SCC indexes (SCC Log/mL) were higher from January to April and from October to December, with peaks of SCC in February and March (rainy season). The lowest results for SCC (p<0.05) were observed from May to September (dry season), with lower average results during the month of May. The highest fat, protein and total solids contents, and the lowest SCC were found during the dry season (p < 0.05), while the lowest concentrations were observed during the rainy season (spring and summer). The increase in SCC was correlated with reduction in lactose, solids nonfat and protein concentrations (p < 0.05), except for SCC range higher than 750,000 cells/mL. In this range, protein content was higher if compared to the levels found in SCC range of 401,000 to 750,000 cells/mL (p < 0.05), but similar to the levels found in milk with SCC range from 201,000 to 400,000 (p > 0.05). This fact may be related to a reduction in milk secretion, and passage of serum proteins into the milk due to a more pronounced inflammatory process. Fat contents were higher (p<0.05) for elevated SCC, which may be linked to lower milk secretion because of mastitis.

Keywords: milk quality, composition, somatic cells