Fecal characteristics and gut bacterial population of weaned pigs fed amino acid-supplemented diets varying in crude protein and fermentable carbohydrate contents

•Dried citrus pulp-enriched diets improved fecal consistency score in weanling pigs.•Low-protein diets with added dried citrus pulp reduced coliform counts.•There was an age-dependent shift in pig bacterial population postweaning.•Dietary crude protein and citrus pulp contents did not change lactobacilli counts. A 28-day study was conducted to evaluate the effects of dietary crude protein (CP; high- and low-CP diets) and dried citrus pulp (DCP; 0 and 7.5%) contents on fecal consistency score and intestinal bacterial enumeration. A total of 108 early-weaned piglets (21 days of age; 5.82 ± 0.16 kg initial body weight) were assigned to 1 of 4 dietary treatments in a 2 × 2 factorial arrangement, with 9 replicate pens per treatment and 3 pigs per pen. The high-CP diets consisted of feeding 20 and 21% CP contents throughout phase 1 (1 to 14 day) and phase 2 (15 to 28 day), respectively. For the low-CP diets, CP contents were reduced by 4 percentage units as compared with the high-CP diets in both phases. Crystalline amino acids (AA) were supplemented to maintain an ideal AA pattern. Feces were scored for consistency during the first 7 days postweaning. Digesta samples from the ileum, cecum, and colon were collected on days 7 and 28 postweaning to determine total coliform and lactobacilli counts. There were no CP x DCP interactions for fecal consistency scores. Although fecal consistency scores were unaffected by the dietary CP contents, adding 7.5% DCP to the diet reduced (P ≤ 0.03; days 1 and 3) and tended to reduce (P ≤ 0.09; days 2 and 5) the incidence of soft feces. On day 7 postweaning, reducing dietary CP inclusion resulted in decreased (P < 0.05) ileal and colonic coliform population in pigs fed diets containing DCP. Additionally, adding 7.5% DCP to the diet decreased (P < 0.05) cecal coliform counts only for pigs fed the low-CP diet on day 7. On day 28 postweaning, there were no treatment effects on coliform population in the ileum, cecum, and colon. Ileal, cecal, and colonic counts of lactobacilli were similar among treatments on days 7 and 28 postweaning. An effect of sampling day was found for ileal coliform (P < 0.01) and cecal lactobacilli (P = 0.04) counts, with greater bacterial populations observed on day 7 when compared with day 28 postweaning. In summary, adding 7.5% DCP to low-CP AA-supplemented diets decreased coliform bacteria proliferation in piglet hindgut immediately after weaning.