Weaning as Stressor for Calf Welfare.

Weaning is a critical period for calves, affecting their well-being, health, and productivity. The present study analyzed 61 calves to evaluate the effects of weaning as a stress factor by monitoring hematological, biochemical, and immune parameters. Blood samples were collected at the start of weaning at 130-135 days (T0), 3 (T1) and 7 (T2) days later, and finally at 150 days of age. The results showed changes in the levels of cortisol, inflammatory cytokines (TNF-α, INF-γ and IL-8) and acute-phase proteins. Alterations in white blood cells were also observed, such as neutrophilia and lymphopenia, which are typical signs of an adverse stress response. Biochemically, the switch from milk to solid food caused imbalances in protein, cholesterol, and triglyceride levels, indicating a relevant metabolic adaptation. Serum electrophoresis showed a decrease in albumin and an increase in γ-globulins, a sign of immune maturation. The results suggest that weaning is one of the most important stressors for calves, with both physiological and immune effects. However, this practice is necessary for breeding productivity. Future research could investigate the role of genetics and environment in weaning resilience to further optimize breeding practices.