Zuprevo

Two subsets of calves in Herd 2 (n = 235) were mass treated for BRD in August 2016, according to the USMARC standard operating procedure (SOP) for intervention in disease outbreaks (Fig. 1). At dam prebreeding processing (approximately June), the dams and their calves were split into three breeding groups based on dam age. During breeding, groups were separated by at least one pasture, so no breeding groups shared fence-line contact at this time. On August 5, 2016, calves in one breeding group (n = 93 study calves) were mass treated for BRD following the observation by the attending veterinarian that approximately 15–20% of the calves were displaying clinical signs of BRD, including: cough, nasal discharge, increased respiratory rate, lethargy, and anorexia. Calves were individually restrained in a squeeze chute for sample collection (as described above) and treatment (Draxxin (tulathromycin; macrolide), Zoetis) then returned to their pasture. On August 12, 2016, a second breeding group (n = 142 study calves) was mass treated with a different antibiotic (Zuprevo (tildipirosin; macrolide), Merck) following the observation that 25–30% of the calves in that pasture were displaying clinical signs of BRD. They were similarly sampled, treated, and returned to their pasture. All treatment decisions were made by the attending veterinarians and carried out according to SOP.

The study was conducted using a randomized complete block experimental design in which blocks of cattle were defined based on source, date of arrival to the feedlot, and study start date. Pen served as the experimental unit to evaluate both health and growth performance variables. Pairs of pens were considered a block, each consisting of 100 animals, 50 per treatment group. Each block consisted of a truck-load of cattle, received and processed on the same day, and blocks of cattle completed the study on the same day. Cattle were purchased in 100 animal lots for this experiment. End point of the study was at cattle harvest.
Treatments consisted of: (1) tulathromycin metaphylaxis (Draxxin, Zoetis, 2.5 mg/kg BW) followed by ceftiofur crystalline free acid (Excede, Zoetis, 6.6 mg/kg BW) and danofloxacin (Advocin, Zoetis, 8 mg/kg BW) for subsequent first and second as-needed BRD treatment, respectively (TCD) or (2) tildipirosin metaphylaxis (Zuprevo, Merck Animal Health, 4 mg/kg BW) followed by florfenicol-flunixin meglumine (Resflor Gold, Merck Animal Heatlh, 40 mg/kg BW florfenicol; 2.2 mg/kg BW flunixin meglumine) and enrofloxacin (Baytril, Elanco Animal Health, 12.5 mg/kg BW) for subsequent first and second as-needed BRD treatment, respectively (TFFE). Treatment assignment is illustrated in Table 2.