RESUMO
Antimicrobial metaphylaxis of high-risk cattle entering the feedlot is a common management strategy implemented against bovine respiratory disease (BRD). Typically, following a prescribed postmetaphylactic interval (PMI), animals displaying clinical signs of BRD are pulled from the feedlot pen and treated with antimicrobials when treatment criteria are met. The objective of this study was to compare 2 distinct sequential BRD treatment protocols each consisting of a metaphylactic antimicrobial plus 2 potential subsequent as-needed treatment antimicrobials. Heifers at high-risk for BRD (n = 1000; initial BW = 229 kg ± 1.6) purchased from sale barns in the southeastern U.S. were transported to a contract research feedlot in Nebraska and randomly assigned to 1 of 2 experimental groups (10 blocks of 100 animals each; 50 per treatment group). Experimental groups consisted of: (1) tulathromycin metaphylaxis (2.5 mg/kg) followed by ceftiofur crystalline free acid (6.6 mg/kg) and danofloxacin (8 mg/kg) for subsequent first and second as-needed BRD treatment, respectively (TCD) or (2) tildipirosin metaphylaxis (4 mg/kg) followed by florfenicol-flunixin meglumine (40 mg/kg florfenicol; 2.2 mg/kg flunixin meglumine) and enrofloxacin (12.5 mg/kg) for subsequent first and second as-needed BRD treatment, respectively (TFFE). Following expiration of the 7-d PMI, calves that showed signs of clinical BRD were pulled and examined to determine if treatment was necessary based on a clinical attitude score (CAS). Heifers with a CAS of 1 accompanied by ≥40°C rectal temperature, and all heifers with a CAS ≥ 2 regardless of rectal temperature, received the appropriate first-treatment antimicrobial. Upon relapse, following expiration of the post-treatment interval (PTI), heifers received the appropriate second-treatment antimicrobial. In the first 90 d, calves in the TFFE experimental group received more first-treatments than calves in the TCD experimental group (P = 0.054) and resulted in 50% greater mortality (P < 0.043) relative to the TCD heifers. From d 0 to closeout, first-treatment morbidity as well as mortality were greater in TFFE relative to TCD (P ≤ 0.032). Growth performance did not differ between treatments in the first 90 d; however, ADG was greater (P = 0.033) and G:F improved (P = 0.014) at closeout in TCD versus TFFE on a deads-in basis. Closeout economics revealed a $50.78/animal greater profit in the TCD experimental group relative to TFFE.
RESUMO
A cross-sectional prospective cohort study including 1026 heifers administered tulathromycin due to high risk of clinical signs of bovine respiratory disease (BRD), measured poor association between BRD clinical outcomes and results of bacterial culture and tulathromycin susceptibility from BRD isolates of deep nasopharyngeal swabs (DNS) and adequate association with viral polymerase chain reaction (PCR) results from nasal swabs. Isolation rates from DNS collected on day-0 and at 1st BRD-treatment respectively were: Mannheimia haemolytica (10.9% & 34.1%); Pasteurella multocida (10.4% & 7.4%); Mycoplasma bovis (1.0% & 36.6%); and Histophilus somni (0.7% & 6.3%). Prevalence of BRD viral nucleic acid on nasal swabs collected exclusively at 1st BRD-treatment were: bovine parainfluenza virus type-3 (bPIV-3) 34.1%; bovine viral diarrhea virus (BVDV) 26.3%; bovine herpes virus type-1 (BHV-1) 10.8%; and bovine respiratory syncytial virus (BRSV) 54.1%. Increased relative risk, at 95% confidence intervals, of 1st BRD-treatment failure was associated with positive viral PCR results: BVDV 1.39 (1.17-1.66), bPIV-3 1.26 (1.06-1.51), BHV-1 1.52 (1.25-1.83), and BRSV 1.35 (1.11-1.63) from nasal swabs collected at 1st BRD-treatment and culture of M. haemolytica 1.23 (1.00-1.51) from DNS collected at day-0. However, in this population of high-risk feeder heifers, the predictive values of susceptible and resistant isolates had inadequate association with BRD clinical outcome. These results indicate, that using tulathromycin susceptibility testing of isolates of M. haemolytica or P. multocida from DNS collected on arrival or at 1st BRD-treatment to evaluate tulathromycin clinical efficacy, is unreliable.