Random metaphylaxis effects on health outcomes, complete blood count, antimicrobial use, and growth performance of high-risk beef steers

Authors: HANRATTY, ASHLEE - Texas Tech University; Sanchez, Nicole; Broadway, Paul; Carroll, Jeffery - Jeff Carroll; HOFFMAN, ASHLEY - Texas Tech University; MANAHAN, JEFF - Texas Tech University; MCDANIEL, ZACH - Texas Tech University; SMOCK, TAYLOR - Texas Tech University; DORNBACH, COLTEN - Texas Tech University; LINE, DALTON - Texas Tech University; THEURER, MILES - Veterinary Research And Consulting Services Llc; GALYEAN, MICHAEL - Texas Tech University; HALES, KRISTIN - Texas Tech University

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2023
Publication Date: 12/1/2023
Citation: Hanratty, A.N., Sanchez, N.C., Broadway, P.R., Carroll, J.A., Hoffman, A.A., Manahan, J.L., McDaniel, Z.S., Smock, T.M., Dornbach, C., Line, D., Theurer, M.E., Galyean, M.L., Hales, K.E. 2023. Random metaphylaxis effects on health outcomes, complete blood count, antimicrobial use, and growth performance of high-risk beef steers. Applied Animal Science. 39:380-390. https://doi.org/10.15232/aas.2023-02458.
DOI: https://doi.org/10.15232/aas.2023-02458

Interpretive Summary: One of the biggest issues affecting the cattle industry is bovine respiratory disease (BRD). Nearly 90% of U. S. feedlots have reported BRD as the most frequent disease. Giving antimicrobials to an entire group is one of the most common tools used for the treatment and prevention of BRD. This method is imprecise and costly because antimicrobial drugs are given to cattle that are healthy and would otherwise not need to be treated. A study was conducted to determine if it was possible to treat less cattle within a group with antimicrobials without negative effects on health or performance. Beef steers were given antimicrobials at 0, 33, 66 and 100% of steers per pen, and health and performance were measured. Data from this study found that antimicrobials can be given to 66% of cattle per pen at arrival without increasing illness while increasing growth. Random antimicrobial treatment is a potential method for decreasing antimicrobial use while at the same time maintaining health and growth of high-risk beef cattle. Data from this study will be of interest to scientists and producers in the area of beef cattle health and performance.

Technical Abstract: Our objectives were to evaluate the effects of random metaphylaxis administered at feedlot arrival to 0, 33, 66, or 100% of high-risk beef cattle on clinical health, growth performance, complete blood cell counts, and antimicrobial use during a 35-d receiving period. Crossbred beef steers (n = 216; arrival BW = 197 ± 6.4 kg) were used in a generalized complete block design consisting of 2 source blocks, each with 4 BW blocks, and 4 treatments. Experimental treatments and steers were randomly assigned to pen within source block: 1) negative control, subcutaneous injection with sterile saline (0M); 2) 33% of steers/pen given metaphylaxis at random with tildipirosin (33M); 3) 66% of steers/pen given metaphylaxis at random with tildipirosin (66M); and 4) positive control; conventional metaphylaxis given to 100% of steers with tildipirosin (100M). Body weight and blood samples for quantification of complete blood count 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 with an antibiotic for bovine respiratory disease (BRD) once was greater (P < 0.01) for 0M and 33M than for 66M and 100M. Neither BW on d 35 nor ADG from d 0 to 35 differed among treatments (P > 0.65), but DMI and DMI as a percentage of BW from d 0 to 35 was greater (P < 0.03) for 66M and 100M than for 0M and 33M. No differences in hematological variables were detected among treatments (P > 0.19), whereas all complete blood count variables were affected by day (P < 0.01), except for mean corpuscular hemoglobin concentration (P = 0.81). Most notably, the neutrophil:lymphocyte ratio was greater (P < 0.01) on d 0 than on d 14 and 35. These data suggest that arrival metaphylaxis can be randomly administered to 66% of cattle without increasing BRD morbidity, while simultaneously increasing DMI similar to conventional metaphylaxis. Random metaphylaxis could be a viable method to decrease antibiotic use in the feedlot industry, while improving health outcomes and growth performance of high-risk beef cattle.