Impact of “Raised without Antibiotics” Beef Cattle Production Practices on Occurrences of Antimicrobial Resistance

What is it about?

Although the recently implemented (January 2017) regulations are expected to reduce their use, the majority of antimicrobials used in the United States (U.S.) are for food-animal production. Thus, there remains a concern that typical antimicrobial use patterns for food-animal production contribute greatly to the occurrence of antimicrobial resistance (AMR). Fecal AMR levels for U.S. beef cattle produced "conventionally" (no restrictions on antibiotic use other than regulatory compliance) and "raised without antibiotics" (no antimicrobial use including ionophores) were assessed over a 12-month period using cultural and genetic methods. Individual AMR levels were either similar between production systems or slightly elevated in conventional animals. Since the scale of AMR reductions in feces from raised without antibiotics cattle were small or nonexistent, further restrictions on antimicrobial use in U.S. beef production are unlikely to reduce the occurrence of antimicrobial-resistant human infections. However, to ensure judicious antimicrobial use, the animal health, economic, and AMR impacts of shorter duration in-feed antimicrobial administration should be examined.

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Why is it important?

The majority of antimicrobial (AM) use in the United States is for food-animal production, leading to concerns that typical AM use patterns during “conventional” (CONV) beef cattle production in the United States contribute broadly to antimicrobial resistance (AMR) occurrence. In the present study, levels of AMR were generally similar between CONV and “raised without antibiotics” (RWA) cattle. Only a limited number of modest AMR increases was observed in CONV cattle, primarily involving macrolide-lincosamide-streptogramin B (MLS) and tetracycline resistance. Macrolides (tylosin) and tetracyclines (chlortetracycline) are administered in-feed for relatively long durations to reduce liver abscesses. To ensure judicious AM use, the animal health, economic, and AMR impacts of shorter duration in-feed administration of these AMs should be examined. However, given the modest AMR reductions observed, further reductions of AM use in U.S. beef cattle production may not yield significant AMR reductions beyond MLS and tetracycline resistance.