Invited Review: Antimicrobial Use and Antimicrobial Resistance in Pathogens Associated with Diarrhea and Pneumonia in Dairy Calves

Simple Summary Antimicrobial use (AMU) is the most important driver of antimicrobial resistance (AMR), and AMU in dairy calves accounts for a substantial amount of total AMU on dairy farms. However, an overview of AMU and AMR in dairy calves is lacking for the design of an AMU stewardship program. In this review, we summarize AMU and AMR data for dairy calves. We found large variation in AMU among herds in different regions, which indicates possibilities for reducing AMU. Antimicrobial resistance seemed to be associated with the types of antimicrobials used in specific regions. Farm type (conventional vs. organic) was associated with AMU but not with AMR. Management factors, such as feeding of calves and prophylactic use of antimicrobials, also related to AMR. This review provides an overview of AMU and AMR data for dairy calves and outlines opportunities for antimicrobial stewardship in dairy calves. Antimicrobial use (AMU) is the major driver of antimicrobial resistance (AMR) among bacteria in dairy herds. There have been numerous studies on AMU and AMR in dairy cows; however, studies on AMU and AMR in dairy calves are limited. A comprehensive overview of the current state of knowledge of AMU and AMR among pathogens in dairy calves is important for the development of scientifically supported and applicable measures to curb antimicrobial use and the increasing risk of AMR. Therefore, we performed a systematic review of research on AMU and AMR in dairy calves. A total of 75 publications were included, of which 19 studies reported AMU data for dairy calves and 68 described AMR profiles of the four most prevalent bacteria that are associated with calf diarrhea and calf pneumonia. Large variation in AMU was found among herds across different regions. There seems to be a positive association between exposure to antimicrobials and occurrence of resistance. Most AMU was accounted for by treatment of diseases, while a small proportion of AMU was prophylactic. AMU was more common in treating calf diarrhea than in treating pneumonia, and the resistance rates in bacteria associated with diarrhea were higher than those in pathogens related to pneumonia. Organic farms used significantly fewer antimicrobials to treat calf disease; however, the antimicrobial resistance rates of bacteria associated with calf diarrhea and pneumonia on both types of farms were comparable. Feeding waste or pasteurized milk was associated with a higher risk of AMR in pathogens. Altogether, this review summarizes AMU and AMR data for dairy calves and suggests areas for future research, providing evidence for the design of antimicrobial use stewardship programs in dairy calf farming.

Automated summary

Antimicrobial use is a major driver of antimicrobial resistance in dairy herds, and there is a lack of overview on antimicrobial use and resistance in dairy calves. This review provides a summary of antimicrobial use and resistance data in dairy calves and suggests possibilities for reducing antimicrobial use.