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

Authors: DUTTLINGER, ALAN - Purdue University; CENTENO MARTINEZ, RUTH - Purdue University; MCCONN, BETTY - Orise Fellow; KPODO, KOUASSI - Purdue University; Lay Jr, Donald; RICHERT, BRIAN - Purdue University; JOHNSON, TIMOTHY - Purdue University; Johnson, Jay

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2021
Publication Date: 3/23/2021
Citation: Duttlinger, A.W., Centeno Martinez, R.E., Mcconn, B.R., Kpodo, K.R., Lay Jr, D.C., Richert, B.T., Johnson, T.A., Johnson, J.S. 2021. Replacing dietary antibiotics with 0.20% L-glutamine in swine nursery diets: impact on intestinal physiology and the microbiome following weaning and transport. Journal of Animal Science. 99(6). https://doi.org/10.1093/jas/skab091.
DOI: https://doi.org/10.1093/jas/skab091

Interpretive Summary: Weaning and transport are necessary in swine production despite the potential for decreased health, performance, and welfare of young pigs. Dietary antibiotics have routinely been provided to improve overall health in order to help pigs overcome the effects of weaning and transport stress. However, despite the advantages to pig health and welfare, U.S. swine producers are working to limit or reduce dietary antibiotic use due to antibiotic resistance concerns. Unfortunately, this can have the unintended effect of reducing pig health and research demonstrates that eliminating prophylactic antibiotics increases the rate of therapeutic treatments for disease. The use of L-glutamine as a feed supplement has been recommended to reduce weaning stress in pigs and recent work by our group directly comparing supplementary L-glutamine to dietary antibiotics has described either improved or maintained growth performance in pigs provided diets supplemented with L-glutamine when compared to traditional dietary antibiotics. Although, the mechanism(s) involved in the aforementioned L-glutamine advantages relative to dietary antibiotics are still unclear, they may be related to improved intestinal health and an altered microbiome. Therefore, the study objectives were to 1) evaluate the impact of replacing dietary antibiotics with L-glutamine on the intestinal health of pigs in a production environment following weaning and transport, and 2) to determine whether intestinal microbiota was altered in pigs provided L-glutamine when compared to those provided dietary antibiotics following weaning and transport. It was determined that diets supplemented with L-glutamine improved intestinal health similarly to dietary antibiotics as shown by the improvements in intestinal morphology compared to pigs not provided dietary antibiotics. In addition, dietary antibiotics improved indicators of intestinal growth. While L-glutamine improved intestinal health, it did not greatly alter the microbiota composition, but the microbiota composition was altered in pigs fed dietary antibiotics. Therefore, it is likely that L-glutamine does not directly interact with the microbiota but instead improves intestinal health by providing nutrients directly to the intestinal cells.

Technical Abstract: 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 on the effects of replacing AB with GLN on intestinal physiology and the microbiome is limited. Therefore, the study objective was to evaluate the impact of replacing AB with GLN on intestinal physiology and the microbiome of pigs in a production environment following weaning and transport. Based on previous research, we hypothesized that removing AB would have a negative impact on intestinal physiology but result in a more diverse microbiome, whereas GLN supplementation would have similar effects on intestinal physiology as AB but with increased microbial diversity. 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 no antibiotics (NA) fed for 14 d. From d 14 to 34, pigs were fed common antibiotic 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 increased (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.