**4. Conclusions**

The economic impacts of cattle disease on the beef cattle industry still remain significant, with BRD being the most significant health problem in modern feedlot industry in North America. The BRD is commonly associated with pneumonia in nursing beef calves and recently weaned feedlot cattle and often occurs within the first 45 days after feedlot placement. The BRD is considered as one of the most significant health problems in the beef industry accounting for economic losses that surpass those incurred by all other diseases of cattle combined. Treatment and control of BRD in the beef sector are aimed mainly at bacterial pathogens through antimicrobial use (therapeutic and non-therapeutic administration) and vaccination programs. However, recent studies have shown the emergence of bacterial pathogens associated with BRD that are resistant to all classes of antibiotics used to treat BRD. The increase in the multidrug resistance towards these antimicrobials that are being used as metaphylaxis in feedlots necessitates the development of novel methods to mitigate bovine respiratory pathogens in feedlot cattle as alternatives to metaphylactic antimicrobial use. Probiotic and EOs, being two major natural antimicrobial sources, display the potential application of antimicrobial alternative agents against bovine respiratory bacterial pathogens. More research is needed to develop nasal-delivered probiotics or EOs that can inhibit pathogenic bacteria, with limited effects on commensals and respiratory tract, after intranasal administration.
