Implementing Precision Antimicrobial Therapy for the Treatment of Bovine Respiratory Disease: Current Limitations and Perspectives

The therapeutic efficacy of an early treatment protocol with an infection-stage adjusted fluoroquinolone regimen was evaluated in a field study on Young Bulls (YB) presenting signs of Bovine Respiratory Disease (BRD). A total of 195 YB (Charolais, Limousin and Rouge-des-Pres breeds) from 6 farms implementing or not prophylactic antimicrobial treatments (PROPHY or absence) were randomly assigned to one of two experiment groups based on time of detection of BRD and first line marbofloxacin regimen, early adjusted dose (E2) or late standard dose (L10). Each YB was administered orally a reticulo-rumen bolus, allowing continuous monitoring of ruminal temperature. In the E2 group, YB presenting early signs of BRD, i.e. an increase in ruminal temperature over 40.2 °C and persisting more than 12h, confirmed by a clinical examination showing no or mild signs of BRD, were given 2 mg/kg of marbofloxacin. In the L10 group, YB presenting moderate or severe signs of BRD at visual inspection, confirmed at clinical examination, were given 10 mg/kg of marbofloxacin. If needed, YB were given a relapse treatment. The YB were followed for 30 days. The proportions of 1st and relapse treatments were calculated, as well as the therapeutic efficacy at d10. In the E2 group, the 1st line treatments proportion was significantly higher (P< 0.05), while the relapse treatments proportion tended to be higher (P=0.08), than in the L10 group. Evolution of Clinical Scores (CS) of diseased YB was followed for 10 d. In both groups, CS and rectal temperature decreased significantly 24 h after treatment (P< 0.05). Treatment incidences (TI) representing antimicrobial consumption assessed on used daily doses (UDD) were calculated. Antimicrobial consumption of marbofloxacin and relapse treatments were not significantly different between the groups. These values were strongly influenced by the recourse to a prophylactic antimicrobial treatment, accounting for more than 90% of the antimicrobial amount in the herds implementing prophylaxis. The higher number of treatments in the groups treated on the basis of ruminal temperature monitoring, the accuracy of the detection method and the necessary conditions to implement precision antimicrobial therapy in the field are discussed in this article.