Effect of early antibiotic intervention on specific bacterial communities and immune parameters in the small intestine of growing pigs fed different protein level diets.

Antibiotics are designed to affect gut microbiota and subsequently gut homeostasis. However, limited information exists about short- and long-term effects of early antibiotic intervention (EAI) on gut homeostasis (especially for the small intestine) of pigs following antibiotic withdrawal. We investigated the impact of EAI on specific bacterial communities, microbial metabolites and mucosal immune parameters in the small intestine of later-growth-stage pigs fed with diets differing in CP levels. Eighteen litters of piglets were fed creep feed with or without antibiotics from day 7 to day 42. At day 42, pigs within each group were offered a normal- or low-CP diet. Five pigs per group were slaughtered at days 77 and 120. At day 77, EAI increased Enterobacteriaceae counts in the jejunum and ileum and decreased Bifidobacterium counts in the jejunum and ileum (P < 0.05). Moreover, tryptamine, putrescine, secretory immunoglobulin (Ig) A and IgG concentrations in the ileum and interleukin-10 (IL-10) mRNA and protein levels in the jejunum and ileum were decreased in pigs with EAI (P < 0.05). At day 120, EAI only suppressed Clostridium cluster XIVa counts in the jejunum and ileum (P < 0.05). These results suggest that EAI has a short-term effect on specific bacterial communities, amino acid decarboxylation and mucosal immune parameters in the small intestine (particularly in the ileum). At days 77 and 120, feeding a low-CP diet affected Bifidobacterium, Clostridium cluster IV, Clostridium cluster XIVa and Enterobacteriaceae counts in the jejunum or ileum (P < 0.05). Moreover, feeding a low-CP diet increased the concentrations of Igs in the jejunum and decreased pro-inflammatory cytokines levels in the jejunum and ileum (P < 0.05). At day 120, feeding a low-CP diet increased short-chain fatty acid concentrations, reduced ammonia and spermidine concentrations and up-regulated genes related to barrier function in the jejunum and ileum (P < 0.05). These results suggest that feeding a low-CP diet changes specific bacterial communities and intestinal metabolite concentrations and modifies mucosal immune parameters. These findings contribute to our understanding on the duration of the impact of EAI on gut homeostasis and may provide basis data for nutritional modification in young pigs after antibiotic treatment.

Antibiotic-induced alterations of the gut microbiota and microbial fermentation in protein parallel the changes in host nitrogen metabolism of growing pigs.

Gut microbes, especially those in the large intestine, are actively involved in nutrient metabolism; however, their impact on host nitrogen (N) metabolism remains largely unknown. This study was designed to investigate the effects of feeding a cocktail of antibiotics (AGM) (ampicillin, gentamycin and metronidazole) on intestinal microbiota, N utilization efficiency, and amino acid (AA) digestibility in cannulated pigs, with the aim of exploring the impact of gut microbiota on host N metabolism. In total, 16 piglets were surgically fitted with a simple distal ileal T-cannula and a jugular venous catheter. The pigs were fed a basal diet without antibiotics (control; CON) or with antibiotics (antibiotic; ANTI), for 2 weeks. The results showed that feeding AGM did not affect weight gain or digestive enzyme activity. The antibiotics increased the concentration of urea N (P<0.05). However, they reduced N utilization, and the total tract apparent digestibility of isoleucine, methionine, valine, tyrosine and total AA (P<0.05). Furthermore, the antibiotics increased the terminal ileum apparent digestibility of CP, phenylalanine, valine, alanine, tyrosine and total AA (P<0.05). AGM markedly altered the composition of the microbiota in the ileum and feces, with a reduction in populations of Bifidobacterium, Lactobacillus and Ruminococcus, and an increase in the abundance of Escherichia coli (P<0.05). The antibiotics also significantly increased the concentration of cadaverine and ammonia, both in ileal digesta and feces (P<0.05), suggesting a marked impact on N metabolism in the intestine. The analyses indicated that the alteration of gut microbiota was correlated with the apparent digestibility of CP and AA in the intestine. These findings suggest that the AGM-induced alteration of gut microbiota may contribute to the change in intestinal N metabolism, and consequently, N excretion from the body. These results also suggest that antibiotics could have a significant effect on host N metabolism. The present study contributes to our understanding of the effects of antibiotics and provides a rational scientific basis for diet formulation during AGM use.