Effects increasing dietary L-glutaine to replace antibiotics on pig health and performance following weaning and transport

Previous research indicates that supplementing nursery diets with 0.20% L-glutamine (GLN) provides similar growth and health benefits as dietary antibiotics, but it is unknown whether greater inclusion levels will provide additional benefits. Therefore, the study objective was to evaluate the impact of replacing dietary antibiotics (A) with increasing levels of GLN on growth performance, health status, and production costs in pigs following weaning and transport. We hypothesized that withholding A would negatively impact performance and health, and that diet supplementation with 0.20% to 1.00% GLN would incrementally improve health and productivity compared to A. Mixed sex pigs (N = 308; 5.64 ± 0.06 kg BW) were weaned (19.1 ± 0.2 d of age) and transported in central Indiana during the autumn of 2017. Pigs were blocked by BW and allotted to 1 of 7 dietary treatments (n = 8 pens/dietary treatment); A [chlortetracycline (441 ppm) + tiamulin (38.6 ppm)], no antibiotics or added GLN (NA), 0.20% GLN, 0.40% GLN, 0.60% GLN, 0.80% GLN, or 1.00% GLN fed for 14 d. On d 15 to 35, pigs were provided NA diets in two phases. Data were analyzed using PROC MIXED in SAS 9.4. Overall, ADG was reduced (P = 0.04; 6.4%) in NA pigs vs. 0.40% GLN or A pigs. Increasing GLN in the diet tended to increase (linear; P = 0.10) ADG. Average daily feed intake was reduced (P = 0.04; 6.9%) in NA pigs vs. 0.40% GLN or A pigs. Overall, d 35 BW was greater (P = 0.01) in 0.80% GLN and A pigs compared to NA, 0.20% GLN, and 0.60% GLN pigs, but no BW differences were detected between 0.80% GLN and A and 0.40% GLN and 1.00% GLN pigs. In addition, d 35 BW was greater (P = 0.01) for 0.40% GLN and 1.00% GLN pigs compared to 0.20% GLN pigs. Increasing GLN in the diet tended to increase (linear; P = 0.08) d 35 BW. Overall, income over feed and therapeutic injectable antibiotics cost for enteric and unthrifty challenges was greater (P = 0.02) in 0.80% GLN pigs compared to NA, 0.20% GLN, and 0.60% GLN pigs, but no income over feed and therapeutic injectable antibiotics cost for enteric and unthrifty challenges differences were detected between 0.80% GLN pigs and 0.40% GLN, 1.00% GLN, and A pigs. In conclusion, GLN supplemented pigs had improved performance and health after weaning and transport compared to the NA pigs with 0.40% GLN being the optimal level while the experimental diets were fed or 0.80% GLN being the most optimal level for the duration of the trial.