Waste milk consumption in Holstein calves: Effect on systemic adaptive immunity

Waste milk (WM) is unsuitable for human consumption due to the presence of drug residues, particularly antimicrobials and anti-inflammatory agent, as well as its high microbial load and somatic cell counts (SCC). Consequently, WM is commonly used to feed dairy calves. This study aimed to evaluate the effects of WM on humoral and cellular immunity in Holstein calves. Calves were assigned to three groups: saleable milk (SM, n = 10), pasteurized waste milk (PWM, n = 10), and raw WM (n = 10). Animals were monitored daily using standardized health scoring systems, and clinical samples were collected on days 7, 21, 35, 49, and 63 of life. Peripheral blood mononuclear cells (PBMC) were isolated, cultured, and stimulated with concanavalin A (ConA), Escherichia coli, Lactobacillus johnsonii, L. reuteri, and Bifidobacterium longum to assess proliferation (BrdU incorporation) and cytokine production (ELISA). Humoral responses were evaluated by serum total protein (STP), Brix refractometry, and IgG concentration. Generalized linear models revealed significant group differences. Clinical profiles were similar among groups. PWM and WM calves exhibited higher monocyte, lymphocyte, and total PBMC counts. Proliferation was greater in SM and PWM calves in response to ConA, E. coli, and L. johnsonii. SM and PWM calves showed higher IL-4 production, whereas WM calves had increased IL-17. IL-10 production was highest in SM. IgG concentrations increased across all groups; however, WM calves exhibited earlier and higher levels, while SM calves maintained the lowest. STP and Brix (%) trends paralleled IgG results. In conclusion, WM elicited an earlier and more intense pro-inflammatory immune response, PWM showed intermediate effects, and SM promoted greater IL-10 production, potentially modulating inflammation in calves.