A Randomized trial to compare the efficacy of tildipirosin and tulathromycin for initial treatment of bovine respiratory disease in naturally exposed commercial feedlot heifers

This clinical trial compared health and performance outcomes between commercial feeder heifers that received either tulathromycin (TUL] or tildipirosin (TLD] for initial treatment of bovine respiratory disease (BRD]. Study heifers, predominately Angus-cross (503.44 lb [228.36 kg] mean body weight], were recently received at a west Texas feedlot from Kentucky, Alabama, and Arkansas, and did not receive metaphylaxis. An experienced pen rider, blinded to treatment groups throughout the study, observed heifers daily for clinical signs of BRD. Six hundred heifers, with either mild BRD and a rectal temperature > 104°F (40°C], or moderate to severe BRD regardless of rectal temperature, were randomly allocated to receive either TUL (100 mg/mL, 1.13 mg/lb [2.5 mg/kg] body weight] or TLD (180 mg/mL, 1.81 mg/lb [4 mg/kg] body weight]. Heifers were randomly allocated to 12 commingled pens, each holding 25 hd of each treatment group (50 hd total/pen]. Data were analyzed with linear mixed models for a randomized complete block design. There were no significant differences among treatment groups for baseline allocation data or for measures of body weight (P=0.52] or average daily gain (deads-out] at re-implant (P=0.20) or close-out (P=0.85]. However, first treatment success was significantly better (P= 0.05] for TUL (67.17%; 95% confidence interval 60.08 - 73.56%] than for TLD cattle (59.26; 51.91 - 66.23%]. Second and third treatment success, and the percent designated as BRD chronics, did not differ significantly between groups (P-values > 0.10], The TUL treated heifers had significantly (P-values = 0.02] less BRD mortality (4.95%; 2.89 - 8.35] and overall mortality (5.94%; 3.61 - 9.61] as compared to TLD treated heifers (10.25%; 6.88 -15.02, and 11.56%; 7.90 -16.62, respectively]. Overall, TUL as initial BRD treatment resulted in significantly better health outcomes as compared to TLD treatment in this study population.