Effects of Alkaline Mineral Complex Water Supplementation in the Diet on the Oxidative Stress, Immunity and Health of Lactating Cows

Mid-lactation represents a critical production phase for high-yield dairy cows, where nutrient imbalance can compromise animal health and farm profitability. This study investigated the effects of dietary alkaline mineral complex (AMC)–water supplementation on milk yield, blood biochemistry, oxidative stress, immunity, hormone secretion and ion status in mid-lactation dairy cows. A total of 120 high-yield mid-lactation Holstein cows were stratified into three milk yield subgroups (EHYG, HYG, MHYG) based on pre-experimental milk yield records. Within each yield stratum, 20 cows were randomly assigned to either the control group or the AMC-supplemented group, resulting in three control subgroups and three AMC-supplemented subgroups (n = 20 per subgroup). Controls received a basal diet, while cows in experimental groups received the basal diet supplemented with diluted AMC concentrate solution (1:4 concentrate to water, v/v) for 90 d. Blood samples were collected on days 0, 15, 30, 45, 60 and 90, and milk samples were obtained on days 0, 30, 60 and 90 to evaluate the production performance, stress and immune status. Dietary AMC supplementation reduced plasma NEFA (p < 0.01) and BHBA concentrations (p < 0.05). For hormone, oxidative-stress and immune indices, significant differences were detected only at discrete individual sampling time points, with no consistent overall treatment effects across the entire experimental period. No significant overall treatment effect of AMC supplementation was observed on the milk yield. These results provide preliminary reference data for alkaline mineral complex additive application in practical mid-lactation dairy production.