January 10, 2019

Interpretive Summary: Pig growth performance and antimicrobial resistance of fecal Escherichia coli

Interpretive Summary: Effects of chlortetracycline alone or in combination with direct fed microbials on nursery pig growth performance and antimicrobial resistance of fecal Escherichia coli.

By: Anne Wallace

In this study published in the December 2018 issue of the Journal of Animal Science, researchers compared the effects of the broad-spectrum antibiotic chlortetracycline (CTC) with direct fed microbials (DFM) in a pig feeding study. The authors looked specifically at how DFM and CTC impacted pig growth performance, and also how they influenced anti-microbial resistance of fecal Escherichia coli in pigs. 

Although antibiotics feed additives are known to effectively increase growth performance in commercial pigs, there is a need for alternatives to antibiotics due to worldwide increasing antimicrobial resistance. Therefore, the researches of this study decided to evaluate the efficacy of DFM feed supplements containing live microorganisms, compared to the antibiotic CTC.

In this study, 300 twenty-one day old pigs were fed different diets containing CTC and/or DFM for 42 days of growth. Two DFMs were used in this study: DFM 1 contained two microorganisms (Bacillus licheniformis and B. subtilus) and DFM 2 contained multiple microorganisms (Enterococcus faecium, Lactobacillus reuteri, Lactobacillus salivarius, Pediococcus acidilactici). Treatments included: (1) negative control with no CTC or DMF, (2) DFM 1 only, (2) DFM 2 only, (3) CTC only, (4) CTC + DFM 1, and (5) CTC + DFM 2. On days 0, 21 and 42, fecal sample collections took place.

Results indicated that pig feed containing CTC produced pigs with significantly better body weight, ADG, and ADFI, when compared to the negative control and DFM 1 and 2 treatments. The initial ADFI up to day 14 was however improved with pigs fed DFM 2 in feed. Increased antibiotic resistance of E. coli to tetracycline family was observed in feed containing CTC. The authors noted that DFM had no effect on antibiotic resistance in this study.

Overall, this study suggests that more research needs to be done on finding viable alternatives to antibiotics to increase the growth performance of pigs. The results of this study did however confirm the known findings of previous studies that antibiotics increases the growth performance of commercial pigs, but also increases fecal antimicrobial resistance. In future studies, using multiple DFM types with higher concentrations in feed, or possibly a combination of DFM with known prebiotics, may be warranted.

To view the full article, visit the Journal of Animal Science.