February 28, 2019

Interpretive Summary: Mannheimia haemolytica challenge in beef steers

Interpretive Summary: Effects of Mannheimia haemolytica challenge with or without supplementation of Saccharomyces cerevisiae boulardii strain CNCM I-1079 on immune upregulation and behavior in beef steers.

By: Anne Wallace

Reducing or replacing antibiotics in livestock feed with safe and cost-effective alternatives, such as direct-fed microbials (DFM), is an important area of study. This paper published in the February 2019 Journal of Animal Science studied the potential benefits of supplementing cattle feed with live yeast (LY) DFM.


S. cerevisiae boulardii is a well-studied probiotic yeast which may impart health benefits, particularly for enteric diarrhea prevention. Bovine respiratory disease (BRD) is a significant cause of morbidity and economic loss in feedlots. The authors of this study therefore chose to study if S. cerevisiae boularii supplementation might provide any protective effects against animals challenged with the respiratory pathogen Mannheimia haemolytica (MH).

In this study, thirty-five Angus steers were fed one of two diets: treatment diet supplemented with LY, or negative control diet without LY (CON). Animals were inoculated with either MH bacteria or phosphate buffer solution (PBS) through the respiratory tract. Immunological, physiological and behavioral responses were evaluated to determine potential benefits of LY supplementation after challenge with MH.

Steers challenged with MH had higher reticulorumen and rectal temperatures compared to PBS animals, suggestive of an acute illness. Feed intake was reduced in MH challenged steers, while immune system blood inflammatory markers (neutrophils, leukocytes and haptogloblin) were elevated, compared to CON. The only significant difference noted in steers fed LY and challenged with MH was an increase in cortisol, a stress hormone that suppresses inflammation.

The results from this study suggest that inoculation with MH can potentially serve as a model for BRD. However, there was no observed benefit of feeding LY to MH-challenged animals. These results suggest that S. cerevisiae boularii supplementation may not be ideal for respiratory pathogens, although it is also possible that the dose or strain of LY may have affected results. Elevation of cortisol suggests LY did impact immune response, although the significance of these findings is unclear. It is also possible that other immune system or inflammatory markers not measured in this study may have been affected by LY treatment. More studies on the effects of LY and DFM on respiratory pathogens in cattle are warranted.  

To view the article, visit the Journal of Animal Science.