For many dairies, feeding waste milk — milk that can’t be sold because of antibiotic residues, high somatic cell counts or other quality issues — is an appealing way to save on calf-rearing costs. It’s calorie-rich, familiar to calves and readily available. However, waste milk is one of the least standardized inputs in calf nutrition as it varies in microbial load, drug residues and inflammatory components. While the short-term economics are easy to calculate, the potential biological impact is less clear.
Most evaluations of waste milk stop at visible outcomes like growth rates or scours. What’s harder to see is how early antigen exposure shapes immune development below the surface. New research from the University of São Paulo shows the immune system of a growing Holstein calf responds differently depending on whether it’s fed salable milk (SM), pasteurized waste milk (PWM) or raw waste milk (WM).
In the study, 30 calves were raised on one of these three liquid diets for the first nine weeks of life and regularly sampled for immune markers and cellular responses. Although overall health scores (temperature, diarrhea prevalence, respiratory signs) didn’t differ among groups, the internal immune story was much more revealing.
Immune Cell Counts and Cytokines Shift With Waste Milk Feeding
Calves fed PWM and WM showed consistent differences in systemic immune markers:
- Serum total protein and Brix values were higher in WM calves.
Total protein and Brix are composite biomarkers influenced by both innate inflammatory response and adaptive humoral immunity. This observed increase likely represents innate immune responses associated with increased microbial and antigen exposure.
- Plasma IgG concentrations did not differ by diet.
Levels followed the expected passive transfer pattern in all groups, with a decline at 21 days as maternal antibodies waned.
- PWM and WM calves exhibited increased circulating immune cell numbers.
Lymphocyte and total mononuclear cell counts were higher compared to SM calves, but these did not translate into greater immune function. Immune cell proliferation in response to bacterial challenge was not impacted by liquid diet.
- Cytokine profiles differed by diet.
SM and PWM calves produced more IL-10, a regulatory cytokine, while WM calves showed higher IL-17, consistent with a more pro-inflammatory profile.
What These Findings Mean for Calf Health Decisions
Together, these findings suggest waste milk feeding alters immune development in subtle but meaningful ways, even when calves appear outwardly healthy.
Several implications stand out:
- Waste milk is not immunologically neutral.
It exposes calves to greater antigenic stimulation, increasing immune cell numbers and inflammatory signaling without improving functional responsiveness.
- Higher TP and Brix values should be interpreted cautiously.
In WM calves, these markers likely reflect inflammatory proteins rather than improved humoral immunity.
- Pasteurization reduces, but does not eliminate, immune effects.
PWM calves consistently showed intermediate immune profiles between SM and WM, supporting pasteurization as a risk-mitigation step rather than a complete solution.
- Early immune skewing might matter most under stress.
An immune system biased toward activation rather than regulation could respond differently during weaning, transport, pathogen exposure or vaccination.
- Diet quality is part of immune programming.
Liquid diet decisions influence not just growth and scours but how the calf immune system is shaped during a critical developmental window.
While this study did not directly assess long-term health or vaccine outcomes, it reinforces an important message for calf programs: What calves drink early in life can influence how their immune systems are wired.
