Effect of dietary protein level on growth performance, indicators of enteric health, and gastrointestinal microbial ecology of weaned pigs induced with postweaning colibacillosis

The effect of dietary CP level on performance, enteric health, and gastrointestinal microbial ecology of weaned pigs challenged with enterotoxigenic Escherichia coli (ETEC) K88 was investigated in a 14-d study. Forty weaned pigs (BW = 5.32 +/- 0.24 kg, mean +/- SD), housed 4 per pen, were randomly assigned to 2 diets (5 pens/diet): 1) 22.5% CP or 2) 17.6% CP supplemented with AA. Diets contained the same amount of ME and standardized ileal digestible Lys, Met + Cys, Thr, and Trp based on the ideal protein ratio. Isoleucine and Val were added to the 17.6% CP diet up to the level in the 22.5% CP diet. On d 8 postweaning, pigs were challenged with 6 mL of ETEC suspension (10(10) cfu/mL) by gavage. Feed disappearance and BW were measured on d 7, 9, 10, 12, and 14 for determination of ADG, ADFI, and G: F. One pig from each pen was serially slaughtered on -1, 3, and 7 d postchallenge (10 pigs/d of slaughter) to evaluate gut morphology, and gut microbial ecology and metabolites. Pigs fed the 22.5% CP diet had greater (P < 0.05) ADG and G: F than those fed the 17.6% CP diet before infection, but performance was similar between the 2 diets after ETEC challenge and overall. On d 3 after challenge, ETEC was not detected in the ileal digesta of pigs fed the 17.6% CP diet but was detected in the ileal digesta of 80% of pigs fed the 22.5% CP diet (5.22 +/- 1.07 cfu/ g, mean +/- SD). Pigs fed the 17.6% CP diet had a greater (P < 0.01) prevalence of order Clostridiales (73 vs. 50%), family Lachnospiraceae (43 vs. 18%), and genus Roseburia (13 vs. 3%) in the colon digesta 7 d after challenge compared with those fed the 22.5% CP diet. The richness and diversity of bacteria in the colon digesta were less (P < 0.05) in pigs fed the 17.6% CP diet than in those fed the 22.5% CP diet at -1, 3, and 7 d postchallenge. Pigs fed the 22.5% CP diet had greater (P < 0.05) ammonia N concentration in the colon digesta on -1 and 7 d after challenge compared with those fed the 17.6% CP diet. Pigs fed the 22.5% CP diet had deeper (P < 0.05) crypts 1 d before challenge, shorter villi 3 d after challenge, and reduced villus height: crypt depth 1 d before and 3 d after challenge compared with those fed the 17.6% CP diet. In conclusion, a reduction in the dietary CP level of weaned pigs from 22.5 to 17.6% with AA supplementation impaired growth performance before, but not after, the ETEC challenge and increased the relative composition of butyrate producing bacteria in the colon digesta after ETEC challenge.