On day 0, each pen of 4 calves is randomly assigned by means of drawing numbers from a hat to receive 1 of 3 treatments; thus, each treatment group consists of 8 calves. Calves in group 1 receive tildipirosinb (4 mg/kg, SC), calves in group 2 receive tulathromycinc (2.5 mg/kg, SC), and calves in group 3 receive saline (0.9% NaCl) solution (1 mL/45 kg, SC; control). The volume of saline solution administered to the calves in group 3 approximates the volume of the assigned antimicrobial administered to the calves of groups 1 and 2. On day 5, all calves are experimentally inoculated (challenged) with 10 mL of PBS solution supplemented with 5% bovine fetal serum containing 1.6×10⁹ CFUs of H somni/mL instilled via a flexible bronchoalveolar lavage tube (length, 3 m; external diameter, 11 mm; internal diameter, 3 mm) that is passed through the nasal passage and nasopharynx to the level of the tracheal bifurcation. Proper placement of the tube at the tracheal bifurcation is verified on the basis of qualitative observations that includ an elicited cough, absence of evidence of esophageal or ruminal placement as determined by smell and lack of tension and failure to observe the tube within the esophagus during placement, the presence of resistance at the carina, and the passage of the tube to a predetermined mark that approximates the distance from the nares to the carina. Following experimental inoculation, the tube is flushed with 60 mL of saline solution and 120 mL of air before it is removed from the calf. On day 8, all calves are weighed, sedated with xylazined (0.25 mg/kg), and transported in a trailer in groups of 4 to 6 calves. Immediately after euthanasia, a necropsy is performed on each calf.

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Rose M, et al. A microbiological assay to estimate the antimicrobial activity of parenteral tildipirosin against foodborne pathogens and commensals in the colon of beef cattle and pigs. J Vet Pharmacol Ther. 2016 Jun;39(3):277-86.

  [2]. Confer AW, et al. Clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni five days after metaphylactic administration of tildipirosin or tulathromycin. Am J Vet Res. 2016 Apr;77(4):358-66.

  [3]. Angell JW, et al. In vitro susceptibility of contagious ovine digital dermatitis associated Treponema spp. isolates to antimicrobial agents in the UK. Vet Dermatol. 2015 Dec;26(6):484-7, e114-5.

  [4]. Michael GB, et al. Increased MICs of gamithromycin and tildipirosin in the presence of the genes erm(42) and msr(E)-mph(E) for bovine Pasteurella multocida and Mannheimia haemolytica. J Antimicrob Chemother. 2012 Jun;67(6):1555-7.

734.02

C₄₁H₇₁N₃O₈

328898-40-4

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Room temperature in continental US; may vary elsewhere