Interpretive Summary: Live yeast and yeast extracts with and without pharmacological levels of zinc on nursery pig growth performance and antimicrobial susceptibilities of fecal Escherichia coli   

By: Dr. Emily Taylor

Feeding pharmacological levels of Zn in the early nursery phase has become a common practice in the swine industry to alleviate post-weaning diarrhea. However, antimicrobial resistance is a concern when feeding these levels. Therefore, the objective of the current study was to determine the effects of pharmacological levels of Zn with or without the addition of the live yeast Saccharomyces cerevisiae strain and yeast-based prebiotics derived from S. cerevisiae on nursery pig growth performance and antimicrobial resistance patterns of E. coli isolated from nursery pig fecal material. 

A total of 360 weanling barrows were assigned in a 2x2 factorial with the main effects of yeast-based pre-and probiotics and pharmacological levels of Zn. No yeast x Zn interactions or effects from yeast additives were observed on any response criteria. Feeding pharmacological levels of Zn during days 0 to 42 increased average daily gain (ADG) and average daily feed intake (ADFI). Fecal samples were taken and analyzed for fecal dry matter and antimicrobial resistance patterns of E. coli. Fecal dry matter was greater on day 4 in pigs fed pharmacological levels of ZN; however, no differences were observed on sampling days 21 or 42. Escherichia coli was isolated from fecal samples to determine the minimal inhibitory concentrations (MIC) of E. coli isolates to 14 different antimicrobials. Isolates were categorized as either susceptible, intermediate, or resistant based using the Clinical and Laboratory Standards Institute (CLSI) guidelines. The addition of pharmacological levels of Zn tended to increase the MIC values of ciprofloxacin; however, these MIC values were still well under the CLSI classified resistant breakpoint for ciprofloxacin. There was no evidence for differences for yeast additives or Zn for antimicrobial resistance of fecal E. coli isolates to any of the remaining antibiotics. No statistical response was observed from the dietary addition of live yeast and yeast extracts for any of the growth, economic, fecal DM, or AMR profiles of fecal E. coli.

In conclusion, adding pharmacological levels of Zn stimulated intake, increased growth, and improved fecal consistency in nursery pigs. Feeding high levels of Zn tended to increase the MIC of fecal E. coli only to ciprofloxacin. Therefore, the authors conclude that short-term use of pharmacological levels of Zn does not increase antimicrobial resistance.

This article is available in the Journal of Animal Science.