Antibiotic Alternatives to Manage BRD

Background

Bovine respiratory disease (BRD) is one of the leading causes of illness and death in newly-received feeder cattle, and BRD prevention and treatment is the main reason that antibiotics are given to newly-received feeder cattle. This team is trying to develop alternatives to antibiotic mass-treatment of feeder cattle for BRD.  

Bovine respiratory disease happens when disease-causing microbes get the upper hand on the harmless or beneficial microbes that are normally found in the respiratory tract. Probiotics aim to support and maintain a healthy microbial population. The research team has previously shown that bacteria in the respiratory tract can be used to stop the growth of pathogens. They have also found that some bacteria in the digestive tract are associated with BRD pathogens. This implies that gut microbes interact with microbes in the respiratory tract to help combat BRD; this communication is known as the gut-lung axis. The team wants to see if (and understand how) feeding probiotics or directly applying them to the nasal cavity helps protect feedlot cattle from BRD.  

Objectives

• Evaluate the effect of local and systemic immune stimulation on respiratory health, 
• Characterize the ability of good bacteria to colonize the respiratory tract of feedlot cattle,  
• Evaluate whether candidate probiotics adhere to mucus in the respiratory tract 
• Evaluate the effect of microbiota transplants on the upper respiratory tract of cattle 
• Develop a community of bacteria that will effectively colonize cattle and stop the growth of BRD pathogens  

What they will do

First, they will study how the gut talks to the lung – how feeding probiotic bacteria to the gut benefits respiratory health in cattle (objective 1). This will be done by initially evaluating immune and bacterial responses in respiratory and gut samples during a digestibility study. Then the team will look at long-term effects of feeding probiotics on the health and performance of feedlot cattle (objective 2). Calves will either be fed a control or probiotic treatment, and sampled at feedlot entry, 30 days on feed, before and after feed transition, and before slaughter. Samples will also be collected if an animal is diagnosed with BRD, prior to treatment. Differences in the microbiomes between healthy, sick, treated, and dead cattle will be compared. Animal performance, carcass traits, and rates of sickness and mortality will be compared. Another feedlot study will be conducted to identify bacteria that can colonize the respiratory tract of cattle. For this, the researchers will transfer bacteria from healthy cattle into the nasal cavity of cattle that are transported before feedlot placement or administered antibiotics at the time of arrival. Respiratory samples will be collected from these cattle and the microbiomes will be compared to identity good bacteria that can colonize animals and inhibit BRD pathogens (objective 4). These samples, in addition to respiratory swabs collected from three cow-calf herds, will be used to establish a diverse culture collection of bacteria (objective 2). Isolates in the collection will be identified and screened for potential to bind respiratory mucus (objective 3) and directly inhibit BRD bacteria. Then, the microbiome data generated from the feedlot studies will be used to develop a community of bacteria from the culture collection that is optimized for colonizing cattle and stopping growth of BRD pathogens (objective 5). 

Implications

Finding ways to cost-effectively prevent BRD while using fewer antimicrobials will help slow the rate of antimicrobial resistance, maintain the effectiveness of antibiotics, and demonstrate the beef industry’s commitment to sustainability.