The effects of sample fat value manipulation on raw cow milk composition and indicators

Values of milk indicators (MIs) can be influenced by sampling errors and milk manipulation. This paper estimated the freezing point depression (FPD) and other MIs drifts which can cause fat movement. That is important for: 1) preparation of reference milk samples (MSs) for proficiency testing and instrument calibrations; 2) estimation of the impact of milk treatment as centrifugation in dairy plants on FPD. Five MSs (A = original milk; milk with modified fat (F) content; B = less F, C = low F, D = more F, E = high F) were created (gravitation F separation at 4 deg C for 12 hours) with the same milk matrix 12 x per year. F averages increased by 4.80% (122.1%) from 1.68 to 6.48% due to manipulation. It increased variability of MIs especially for solids non fat (SNF), lactose (L) and crude protein (CP). Somatic cell count (SCC) averages increased by 803 from 9 to 812 thousand/mL. Correlation F x SCC was 0.85 (P less than 0.001). SNF, L and CP averages decreased by 0.47%, 0.31% and 0.17%, respectively. Correlation coefficients were -0.78, -0.75 and -0.64 (P less than 0.001). Urea decreased along with F increase by 2.9% (r=-0.13). Acetone increased by 47.6% (r=0.21). Electrical conductivity decreased by 6% (r=-0.15). Alcohol stability was reduced by 23.3% (r=-0.15). FPD, titration and actual acidity were not influenced.