Relationship between somatic cell count and milk casein level obtained by two different methods

The purpose of the present work was to investigate the impact of somatic cell count (SCC) on the content of milk casein and to compare the sensitivity of different methods for the determination of the casein level in milk. Two different methods were employed in order to determine the casein level: routine method - infrared spectrophotometry and reference method - Kjeldahl. Data array of 26, 169 milk samples of the livestock control was used to analyse milk casein variation by SCC limits. Mean casein values (investigated by the routine method) varied from 2.47% to 2.8% (2.65 ± 0.09) and casein number (in % on crude protein basis) - CN% varied from 79.5% to 81.1%. The present analysis showed that the relation between SCC and casein content obtained by the routine method correlated significantly (Pearson correlation rp = 0.644, P < 0.05, R2 = 0.414, Spearman correlation rs = 0.786, P < 0.05). Evaluated results obtained by the least squares method, and linear approximation of variation indicators presented a noticeable decline in casein percentage - 0.27%, when SCC increased by 80 × 103/ml, but only when the studies were done by the reference method.