Waste milk consumption in dairy calves: Effects on innate immunity and inflammatory profile.

Waste milk (WM) is commonly used in calf feeding to reduce rearing costs; however, its effects on the innate immune response remain unexplored. Therefore, this study aimed to evaluate the effects of WM on the innate immune response and inflammatory profile of pre-weaned dairy calves. Thirty male Holstein calves were assigned to receive pasteurized waste milk (PWM), saleable milk (SM), and WM (n = 10 in each group). Blood samples were collected on D7, D21, D35, D49, and D63 (days of life) to assess the white blood cell (WBC) count, phagocytic activity of polymorphonuclear cells (PMN), and nitric oxide (NO) production by monocyte-derived macrophages, in addition to the measurement of oxidative stress biomarkers and haptoglobin concentration. A trend towards a higher occurrence of respiratory disease was detected in calves that received WM, followed by PWM. A group effect (P = 0.00) was observed in absolute monocyte values, with higher values found in the WM group. Only the TBARS concentration showed a group × time interaction among all oxidative stress biomarkers, with the highest mean found in calves receiving WM, followed by those receiving PWM and SM. Elevated TBARS concentrations indicated higher lipid peroxidation, which may have resulted from the accumulation of reactive oxygen species (ROS) due to immune challenges from ingesting pathogens present in WM. Haptoglobin concentration was unaffected. WM promoted lipid peroxidation and antioxidant enzyme activity, suggesting a pro-inflammatory effect. The time-effects of PMN phagocytosis reflected the development of the immune system in neonatal calves, which is consistent with previous studies.