Exploring the effect of total and differential somatic cell traits on the mineral profile of milk from individual dairy cows

Despite the routine use of SCS and differential SCC (DSCC) as indirect udder health indicators, few studies explored how these 2 traits and their interaction can affect milk quality, especially in terms of mineral elements. Therefore, this study investigated the effect of SCS, DSCC, and their interaction on the concentration and daily excretion of major minerals (Ca, Mg, K, S, P, Cl, and Na) in bovine milk. A total of 1,060 Brown Swiss cows from 53 commercial herds in northern Italy were individually sampled over a 14-mo period. Milk samples were analyzed for composition using Fourier transform infrared spectroscopy, for SCC and DSCC using flow cytometry, and for mineral concentrations using wavelength-dispersive x-ray fluorescence. Daily mineral quantities (dMQ, g/d) were calculated by multiplying mineral concentration by milk yield (MY). Two mixed linear models were applied: The first assessed mineral concentrations and included MY among the fixed effects; the second model, applied to dMQ traits, excluded MY because it was already integrated into the dependent variable. Results showed that both SCS and DSCC significantly influenced milk mineral concentrations, with Na and P being the most affected. An increase in SCS was associated with an increase of Na, Cl, and P, and a decrease of K concentration. Differential somatic cell count had a larger mineral-specific effect, significantly influencing Na and P concentrations, but not dMQ. The most consistent response was observed for Na, whose concentration increased with SCS, especially in cows with low DSCC. This interaction suggests a potential chronic inflammatory condition and a loss of blood-milk barrier integrity, leading to altered ions transport. Daily mineral outputs were negatively associated with increasing SCS, with Ca, P, K, Mg, and S showing reduced secretion, mainly due to decreased MY in inflamed animals. These findings highlight that, beyond dilution effects, high SCS in milk may reflect a compromised mineral secretion efficiency. The interaction between SCS and DSCC significantly affected the concentrations of Na and Cl, although less pronounced in terms of dMQ, revealing a synergistic effect of SCS and DSCC on milk mineral composition. In conclusion, this study demonstrates that milk mineral profile is significantly influenced by SCS, DSCC, and their interaction, suggesting their valuable use as indicators of udder health and as potential contributors to variations in milk quality traits relevant to dairy processing. These results support the integration of DSCC alongside SCC in routine herd health monitoring and milk quality assessment programs.