Effects of yeast-based pre- and probiotics in lactation diets of sows on litter performance and antimicrobial resistance of fecal Escherichia coli of sows

Lay Summary Feeding sows live yeast and yeast extracts from day 110 of gestation through lactation tended to increase lactation feed intake but did not affect any other sow or litter performance criteria. Live yeast and yeast extracts in the diet had minimal effect on the antimicrobial resistance of fecal E. coli isolates. Regardless of the diet, fecal E. coli isolates were susceptible to 11 of the 14 antimicrobials when sows entered the farrowing house. But most of the antimicrobials were classified as intermediate or with a tendency toward resistance at weaning even though none of these antibiotics were used during the lactation period. Our findings agree with other cross-sectional studies on AMR where high AMR gene levels reported among young pigs were attributed to sow population. Feeding live yeast and yeast extracts tended to increase feed intake during lactation, but had no effects on sow or litter performance. Live yeast and yeast extracts in the diet had minimal effect on the antimicrobial resistance profiles of fecal E. coli isolates during lactation. A total of 80 sows (Line 241; DNA, Columbus, NE) across three farrowing groups were used in a study to evaluate the effect of feeding live yeast and yeast extracts to lactating sows on sow and litter performance and antimicrobial resistance (AMR) patterns of sow fecal E. coli. Sows were blocked by farrowing group, BW, and parity on day 110 of gestation and allotted to 1 of 2 dietary treatments. Dietary treatments consisted of a standard lactation diet with or without yeast-based pre- and probiotics (0.10% Actisaf Sc 47 HR+ and 0.025% SafMannan; Phileo by Lesaffre, Milwaukee, WI). Diets were fed from day 110 of gestation until weaning (approximately d 19 post-farrow). A tendency (P = 0.073) was observed for increased feed intake through lactation when sows were fed a diet with yeast additives compared with the control diet. There was no evidence (P > 0.10) that treatment influenced any other sow or litter performance measurements. Fecal samples were collected upon entry into the farrowing house and at weaning from the first farrowing group (27 sows) to determine the resistance patterns of E. coli. E. coli was isolated from fecal samples and species confirmed by PCR detection of uidA and clpB genes. Microbroth dilution method was used to determine the minimal inhibitory concentrations (MIC) of E. coli isolates to 14 antimicrobials. Isolates were categorized as either susceptible, intermediate, or resistant based on Clinical and Laboratory Standards Institute guidelines. An interaction (P = 0.026) of diet x sampling day was observed for cefoxitin where fecal E. coli showed no evidence of treatment differences (P = 0.237) in MIC values at entry, but sows fed the control diet had lower (P = 0.035) MIC values at weaning compared with sows fed yeast additives. There were no diet main effects (P > 0.10) on the resistance of fecal E. coli. There was an increased (P < 0.02) toward resistance for 11 of the 14 antimicrobials over time. Fecal E. coli were resistant to tetracycline and ceftriaxone at weaning. Fecal E. coli were susceptible or intermediate in all sampling days to the remaining antimicrobials. In conclusion, feeding live yeast and yeast extracts tended to increase feed intake during lactation but did not influence either sow or litter performance measurements or the resistance of fecal E. coli during lactation except for cefoxitin, which had a higher MIC at the end of lactation when yeast additives were present in the diet.