Can Probiotics Enahnce the Respiratory Bacteria to Improve the Health of Beef Cattle?

Background

The immune system is complex. It responds to natural pathogen exposure or vaccination through adaptive immunity against specific pathogens. But innate immunity (e.g., mucus, scavenger cells and various foreign bacteria-killing proteins and other immunomodulators circulating in the blood) is also important. Naturally-occurring bacteria in the respiratory tract may have a beneficial immunomodulatory role and act as first responders against BRD, but this can be disrupted by stress, diet changes, and antibiotics. To be effective, probiotics to supplement these beneficial commensal bacteria need to be able to establish themselves in the respiratory tract without being overwhelmed by existing bacteria (either good or pathogenic) or mucus. These researchers will evaluate how the microbiota of beef cattle impact host immunity, then will use this information to develop immunomodulators that confer broad resistance against respiratory pathogens. They will create an artificial respiratory model to study colonization and host responses to bacteria and viruses. The model will be used to identify and characterize bacteria and/or their metabolites that enhance immunity. Promising bacteria/metabolites will be used as an intranasal immunomodulator in a challenge study to measure effectiveness.

Objectives

• Characterize the mucosa-associated bacteria of the upper respiratory tract

• Develop an air-liquid interphase model to characterize respiratory bacteria colonization and interaction with host epithelial cells

• Test the inoculation of a synthetically derived bacterial community on host immunity and pathogen exclusion in challenged calves

What they will do

Study 1: The left and right nasopharynx will be biopsied in 8 healthy steers and 8 BRD cases. The tissue and bacteria collected will be DNA-sequenced and characterized using microscopy.

Study 2: Mucosa will be extracted from the nasal septum or trachea of healthy slaughter cattle and screened to ensure they’re free of Mycoplasma and BRD viruses. The respiratory mucosa tissue samples will be established in culture media and inoculated with microbes collected from feedlot steers. The tissue culture that maintains the most stable microbial population will be inoculated with previously developed bovine microbes, with or without Mannheimia haemolytica and BHV-1, cultured, and immune responses will be evaluated. The bacterial communities that resist pathogens and optimally stimulate the immune system will be used in Study 3.

Study 3: 24 calves will be given the probiotic cocktail at 6 weeks of age (or not). Deep nasal swabs will be collected to assess bacteria and animal gene expression on d 3, 7 and 14 (as well as animal health), then killed and necropsied for lung evaluation.

Implications

Probiotics that enhance the animal’s immune response and resist pathogen colonization may help improve animal health, reduce losses due to BRD, and reduce the need for antimicrobial use in beef production.