Replacing dietary antibiotics with 0.20% L-glutamine in swine nursery diets: impact on intestinal physiology and the microbiome following weaning and transport

Previous research demonstrates that supplementing 0.20% L-glutamine (GLN) in the diets of newly weaned and transported pigs improves growth rate to a similar extent as providing dietary antibiotics (AB). However, research comparing the effects of GLN versus AB on intestinal physiology and the microbiome is limited. Therefore, the study objective was to compare the effects of supplementing nursery diets with GLN, AB, or no dietary antibiotics (NA) on intestinal physiology and the microbiome of pigs in a production environment following weaning and transport. Mixed sex piglets (N=480; 5.62 ± 0.06 kg BW) were weaned (18.4 ± 0.2 d of age) and transported for 12 hr in central Indiana, for two replicates, during the summer of 2016 and the spring of 2017. Pens were blocked by BW and allotted to 1 of 3 dietary treatments [n = 10 pens/dietary treatment/replicate (8 pigs/pen)]; AB [chlortetracycline (441 ppm) + tiamulin (38.6 ppm)], GLN (0.20% as-fed) or NA fed for 14 d. From d 14 to 34, pigs were fed common AB free diets in two phases. On d 33, villus height:crypt depth tended to be increased (P = 0.07; 7.0%) in GLN and AB pigs vs. NA pigs. On d 33, glucagon-like peptide 2 (GLP-2) mRNA abundance was decreased (P = 0.01; 50.3%) in GLN and NA pigs vs. AB pigs. Crypt depth was increased overall on d 33 (P = 0.01; 16.2%) during the spring replicate compared to the summer replicate. Villus height:crypt depth was reduced (P = 0.01; 9.6%) during the spring replicate compared to the summer replicate on d 33. On d 13, tumor necrosis factor alpha and occludin mRNA abundance was increased (P ≤ 0.04; 45.9% and 106.5%, respectively) and zonula occludens 1 mRNA abundance tended to be greater (P = 0.10; 19.2%) in the spring replicate compared to the summer replicate. In addition, AB pigs had increased (P = 0.01; 101.3%) GLP-2 gene expression compared to GLN and NA pigs. Microbiome analysis indicated that on d 13, dietary treatment altered the microbiota community structure (P = 0.03). Specifically, the AB pigs tended to be distinct from both the NA and GLN pigs (P = 0.08), and Lactobacillus was increased nearly 2-fold in AB compared to NA pigs (q = 0.04) and GLN pigs (q = 0.22). In conclusion, GLN supplementation tended to improve some morphological markers of intestinal health similarly to AB pigs while the microbiome composition in GLN pigs was more similar to NA pigs than AB pigs.