Comparative efficacy of enrofloxacin to that of tulathromycin for the control of bovine respiratory disease and prevalence of antimicrobial resistance in Mannheimia haemolytica in calves at high risk of developing bovine respiratory disease1

Abstract

Bovine respiratory disease (BRD) is the most common cause of morbidity and mortality in North American beef cattle. Mannheimia haemolytica is the bacterial pathogen most often isolated from cattle with BRD, and the prevalence of antimicrobial resistance (AMR) in this organism has increased in recent years. Antimicrobials are commonly used to prevent BRD in cattle at high risk of developing BRD; however, recent work would suggest that this practice might be one factor contributing to the increased prevalence of AMR in M. haemolytica. We hypothesized that the administration of the short-acting fluoroquinolone, enrofloxacin, would be just as effective as the long-acting triamilide, tulathromycin, in preventing BRD but would be less likely to select for AMR M. haemolytica in stocker calves at high risk of developing BRD. Three hundred forty-one stocker calves were enrolled in the study with 172 calves in 4 pens being randomly assigned to treatment with enrofloxacin and 169 calves in 4 pens randomly assigned to treatment with tulathromycin. Calves within each treatment group were allocated to one of 4 replicate pens based on the week of enrollment. Of calves receiving enrofloxacin, 33.7% required treatment for BRD at least once within 45 d after arrival, compared with 18.3% of calves receiving tulathromycin (P = 0.040). The percentages of calves that required more than one treatment for BRD within 45 d after arrival did not differ statistically for those receiving enrofloxacin compared with those receiving tulathromycin (10.5% and 4.7%, respectively; P = 0.107) Likewise, the percentages of calves that died during the 45-d follow-up period did not differ for those receiving enrofloxacin compared with those receiving tulathromycin (12.2% and 10.1%, respectively; P = 0.592). Mannheimia haemolytica was cultured from 11% of calves sampled at arrival and from 50% of calves sampled at revaccination 14 to 17 d later. There was a significanst effect of sampling time on the proportion of calves carrying multidrug-resistant (MDR) isolates, with calves having a higher prevalence of MDR isolates at revaccination than arrival (100% vs. 13%; P < 0.001). Future research evaluating the impact of MDR on response to antimicrobial therapy is necessary.

Antimicrobial Resistance in Members of the Bacterial Bovine Respiratory Disease Complex Isolated from Lung Tissue of Cattle Mortalities Managed with or without the Use of Antimicrobials

“…Bovine respiratory disease (BRD) is the leading cause of morbidity and mortality of North American feedlot cattle [1]. Multiple factors are potentially predisposing to BRD, including stress from weaning [2], transportation, co-mingling at auction markets [3], extreme weather changes [4], and changes in diet [5].…”

“…The bacterial pathogens, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma bovis rapidly proliferate in the nasopharynx as a preliminary step in the development of BRD [5] and these organisms are also routinely detected in the lungs of BRD mortalities [6,7]. M. haemolytica has been the organism most frequently isolated from necropsied lungs of cattle with BRD in many studies [1,2,6,7], although age of cattle sampled, type of BRD, and antimicrobial therapies received also influence BRD organisms recovered [8][9][10].…”

Switching between bacteriostatic and bactericidal antimicrobials for retreatment of bovine respiratory disease (BRD) relapses is associated with an increased frequency of resistant pathogen isolation from veterinary diagnostic laboratory submissions

“…Therefore, tulathromycin is one of the most frequently used antimicrobial drugs for metaphylaxis in the US [5]. However, metaphylaxis treatment with tulathromycin has been associated with a high prevalence of multidrug resistant M. haemolytica shedding in cattle [23, 30]. One explanation for the elevated antimicrobial resistance of M. haemolytica and P. multocida is the long elimination half-life of macrolides results in prolonged exposure to low concentrations of the bacteriostatic agent, which may be contributing to the development of AMR.…”

Characterization and comparison of cell-mediated immune responses following ex vivo stimulation with viral and bacterial respiratory pathogens in stressed and unstressed beef calves1

“…It is estimated that BRD costs the cattle industry in excess of US$1 billion every year (Griffin, 1997;Watts and Sweeney, 2010). One part of the cattle industry that is particularly affected by BRD is the stocker cattle segment (Crosby et al, 2018). These cattle are typically light-weight, unweaned, commingled, and of unknown health status (Snyder et al, 2017).…”