Random metaphylactic effects of tulathromycin on health outcomes, complete blood count, antimicrobial use, growth performance, and Salmonella enterica prevalence in high-risk beef steers

Authors: DORNBACH, COLTEN - Texas Tech University; Broadway, Paul; Sanchez, Nicole; GRANT, MADDIE - Texas Tech University; CANTERBURY, LANDON - Texas Tech University; CHILDRESS, KALLIE - Texas Tech University; SITKA, BLAKE - Texas Tech University; LOEFFLER, TAYLOR - Texas Tech University; GALYEAN, MICHAEL - Texas Tech University; HALES, KRISTIN - Texas Tech University

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bovine respiratory disease (BRD) is the leading cause of sickness and deaths in feedlots. Over 16% of newly received cattle are affected by BRD. Economic losses from BRD can exceed $2 billion annually in the U.S. Metaphylaxis is the practice of treating all cattle with an antibiotic to prevent disease. A recent study found metaphylaxis can be given randomly to 66% of high-risk cattle without increasing BRD sickness or negatively affecting growth performance. A study was conducted in Lubbock, Texas by ARS and university scientists to evaluate random metaphylaxis . Results confirmed previous findings that metaphylaxis can be given randomly to 66% of high-risk beef cattle without increasing sickness or reducing growth. Antibiotic use was also decreased. Yet, Salmonella in feces was unaffected by treatments. These data will be of interest to scientists in the fields of beef cattle production as well as beef producers.

Technical Abstract: We evaluated the effects of random metaphylaxis administered with tulathromycin at feedlot arrival to 0, 33, 66, and 100% of high-risk beef steers on health outcomes, growth performance, complete blood cell count, Salmonella prevalence, and antimicrobial use during a 35-d receiving period. Crossbred beef steers (n = 232; arrival BW = 213 kg ± 6.3 kg) were used in a generalized complete block design consisting of 2 source blocks, each with 4 BW blocks and 4 treatments. Steers were randomly assigned to pen within source block, and experimental treatments were: 1) negative control; s.c. injection with sterile saline (0M); 2) tulathromycin administered at random to 33% of steers within a pen (33M); 3) tulathromycin administered at random to 66% of steers within a pen (66M); and 4) conventional metaphylaxis with tulathromycin administered to 100% of steers within a pen (100M). Body weight, whole blood, and fecal samples were collected on d 0, 14, and 35. Metaphylactic treatment was included in the model as a fixed effect, and BW block within source block was included as a random effect. The percentage of steers treated for bovine respiratory disease once was 108% and 62.2% greater on average for 0M and 33M, respectively, than for 66M and 100M steers (P = 0.01). Neither BW on d 35 nor ADG, DMI, or G:F from d 0 to 35 differed among treatments (P = 0.63). Only reticulocyte count and percentage of eosinophils differed among treatments (P = 0.03), whereas most complete blood cell count variables were affected by day (P < 0.01). Fecal Salmonella concentration and prevalence (P = 0.40) did not differ among treatments but increased from d 0 to 14 before equalizing through d 35 (P < 0.01). These data suggest that metaphylaxis can be administered to 66% of cattle without increasing bovine respiratory disease morbidity or decreasing growth performance. Moreover, random metaphylaxis to 66% of steers at arrival decreased the amount of active drug compound and the number of antimicrobial injections administered in each pen without increasing pathogen shedding compared with administering conventional metaphylaxis to 100% of the pen in high-risk beef steers.