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Glutamine is currently considered a nonessential amino acid for pigs. In this study we investigated whether glutamine is essential during an acute immune challenge. Thirty-six individually housed 20-day old pigs were blocked by location and allotted to one of three purified dietary treatments: 1)contained no L-Glutamine (CON), 2) contained 5% L-Glutamine (GLN), or 3) contained no L-glutamine but was equalized to GLN diet on a nitrogen basis with other nonessential amino acids (AA). Pigs were fed these diets for a 14-day growth assay. On day 7, one half of the pigs from each treatment were injected with 200 µg•kg BW-1 lipopolysaccharide (LPS; the endotoxin synthesized from E. coli) and the remaining pigs were injected with an equal volume of physiological saline (SAL). Average daily gain (ADG; P>0.21), average daily feed intake (ADFI; P>0.79), and feed efficiency (ADG/ADFI; P>0.26) were similar among treatments prior to LPS or SAL injection. During the period after LPS or SAL injection, LPS reduced ADG (0.46 vs. 0.24 lb/d; P<0.0001), ADFI (0.63 vs. 0.47 lb/d; P < 0.005) and ADG/ADFI (0.74 vs. 0.50; P<0.001) by 48%, 25%, and 32%, respectively. However, there were no differences for ADG (P>0.39), ADFI (P>0.95), or ADG/ADFI (P>0.24) between pigs injected with LPS and SAL and fed GLN (Diet x LPS interaction, P<0.06). Intestine length (P<0.0001), full weight (P<0.005), and empty weight (P<0.0005) were reduced by LPS injection compared to SAL injection. Pigs fed GLN and injected with LPS had similar empty small intestine weight compared to pigs fed GLN and injected with SAL (diet x LPS interaction, P<0.07). These data suggest that glutamine is beneficial to improve the growth and health of weanling pigs after an immune challenge.