August 28, 2019

Interpretive Summary: Immunologic and physiologic differences of stressed and unstressed beef calves

Interpretive Summary: Characterization and comparison of cell-mediated immune responses following ex vivo stimulation with viral and bacterial respiratory pathogens in stressed and unstressed beef calves.

By Anne Zinn

A research team from the University of Georgia, Athens recently compared cell-mediated immune responses following ex vivo stimulation with viral and bacterial respiratory pathogens in stressed and unstressed beef calves.

Bovine respiratory disease (BRD) is the most common cause of morbidity and mortality in North American beef cattle and is estimated to cost the cattle industry upwards of $1 billion each year. Specifically, stocker cattle are often most affected because they are typically light-weight, unweaned, commingled, and of unknown health status. Although vaccinated, numerous stressors can affect the efficiency of the vaccination. For these reasons, the objective of this study was to characterize the cell-mediated immune responses of multiple source, highly commingled calves of unknown health history (stressed calves, STR) and compare to a group of calves that were single source, of a known health history, and weaned for 60 d (unstressed calves, UNS).

Peripheral blood mononuclear cells and neutrophils were isolated from each calf and stimulated with viral and bacterial respiratory pathogens. Unstressed calves had greater lymphocyte proliferative responses following stimulation, and PMNs had a greater ability to phagocytose E. coli and S. aureus when compared with STR calves. Also, serum nonesterified fatty acids were higher in STR calves, and serum β-hydroxybutyrate was lower in STR calves. These results suggest that immunologic and physiologic differences exist between STR and UNS calves.

It is important to note that although the impact of stress on the performance of several immune indicators was evaluated, the differences observed were quite small. The threshold points for a decline in immune function capability, as well as the underlying mechanisms for these differences, are unclear.  It is, however, possible that combinations of energy imbalance, stress-induced immunosuppression, and general immune naiveté, may predispose STR calves to an increased risk of morbidity and mortality due to bovine respiratory disease. Further investigation into how the development of a disease is affected while additional factors are controlled is warranted. In addition, the need exists for future research to investigate how these differences contribute to BRD risk and how the modulation or alteration of immune activation and management of physiological balance.

The full paper can be accessed here.