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ARS Home » Plains Area » Lubbock, Texas » Cropping Systems Research Laboratory » Livestock Issues Research » Research » Publications at this Location » Publication #420100
Research Project: Environmental and Management Influences on Animal Productivity and Well-Being Phenotypes

Location: Livestock Issues Research

Title: Effects of a direct-fed microbial on occurrences of antimicrobial resistance in Salmonella enterica, Escherichia coli, and Enterococcus spp. measured longitudinally from feedlot arrival to harvest in finishing beef steers

Author
item HOFFMAN, ASHLEY - Texas Tech University
item DORNBACH, COLTON - Texas Tech University
item FERNANDO, SAMODHA - University Of Nebraska
item Broadway, Paul
item Sanchez, Nicole
item LONG, NATHAN - Texas Tech University
item MCDANIEL, ZACH - Texas Tech University
item SMOCK, TAYLOR - Texas Tech University
item Wells, James
item HALES, KRISTIN - Texas Tech University

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Direct-fed microbials are products that contain live bacteria and/or yeasts. Feeding these products to cattle has the potential to improve growth performance and decrease disease-causing bacteria. Scientists with the USDA-ARS and university collaborators studied changes in bacteria in the feces of cattle from feedlot arrival to harvest. Cattle were fed a novel direct-fed microbial or tylosin, a common antibiotic used to reduce liver abscesses. Results from this study found changes in fecal bacteria over time. Also, no increases in antibiotic resistance were observed when cattle were fed a novel direct-fed microbial. Changes in antibiotic resistance appeared more affected by season. These data will be of interest to scientists in the field of cattle physiology and beef cattle producers.

Technical Abstract: The continuous feeding of antimicrobials, such as tylosin phosphate for the control of liver abscesses, is commonplace in cattle feedlots. A decrease in antimicrobial use in food animal production is desirable, and therefore, interest in direct-fed microbials as an alternative continues to increase. Two-hundred forty Angus beef steers (mean initial BW = 263 kg ± 18.0 kg) were assigned randomly to one of three dietary treatments; negative control, dietary supplement contained no tylosin (NCON); positive control, dietary supplement contained tylosin (PCON); or novel direct-fed microbial fed at 1 g mixture/steer with 1 × 1011 CFU/g (DFM). Fecal samples were collected on days 0, 59, 128 and at study end. Pen and hide swabs were collected two days before harvest and subiliac lymph nodes were collected the day of harvest. All targeted bacterial populations differed across time (p = 0.05), except 128ERYR Escherichia coli. Fecal Salmonella concentration and prevalence differed among dietary treatments (p = 0.02) with NCON having greater fecal Salmonella concentrations than PCON and DFM. No differences in Salmonella prevalence among pen swabs, hide swabs, or subiliac lymph nodes were detected (p = 0.40). Salmonella resistant to tetracycline or cefotaxime was not detected in feces. The effect of treatment differed by day for total and 128ERYR Enterococcus spp. concentrations. Total Enterococcus spp. concentrations were greatest for the DFM treatment on day 128 and at study end (p = 0.01). At study end, 128ERYR Enterococcus spp. concentrations were greatest for PCON (p = 0.01). Total, TETR, COTR, and CTXR E. coli concentrations increased from d 0 to study end among treatments (p = 0.01). These data suggest that the in-feed inclusion of a novel direct-fed microbial is not directly implicated in antimicrobial resistance of feedlot beef cattle.