A third round of feeding trials conducted by a team of USDA Agricultural Research Service and university scientists has again shown that a dietary supplement called L-glutamine can naturally promote growth and wellness in pigs.

Jay S. Johnson, an animal scientist with ARS's Livestock Behavior Research Unit in West Lafayette, Ind., and his Purdue University collaborators are investigating L-glutamine as a natural alternative to using dietary antibiotics. Swine producers had used antibiotics to help piglets cope with stressful events like being weaned from their mothers and then transported, which can lower young animals' immune function, feed intake and growth.

However, a 2017 Veterinary Feed Directive restricted the practice amid concerns it contributed to antimicrobial resistance to medically important antibiotics used to treat human infection. The team's investigation of L-glutamine, a naturally occurring amino acid found in the body and in food, is part of a broader research effort to identify suitable replacements that are just as effective, safe and economical to use.

The latest study is an expansion of trials conducted in 2017 and 2018. As before, groups of piglets were weaned and then transported for 12 hours, simulating what they might experience in a commercial operation. After transport, the piglets were housed in a nursery barn. This time, the researchers supplemented the young animals' diets for 14 days with L-glutamine at one of five feed concentrations: 0.20, 0.40, 0.60, 0.80 or 1.00%. Another group of piglets also received feed with antibiotics (chlortetracycline and tiamulin) but no supplemental L-glutamine, and a final group received a non-supplemented diet.

Highlighted results of a paper published in Translational Animal Science are below:

• As with prior trials, L-glutamine-treated pigs performed similarly to those in the antibiotics group, and both of these groups fared better than piglets given non-supplemented feed.
• The study results indicate that the increased weight gain and other benefits of treating piglets with L-glutamine above the original .20% test can be as profitable as using dietary antibiotics.
• 0.40% L-glutamine was the optimal supplementation level for improving pig welfare and performance immediately after weaning and transport, while 0.80% appeared to offer the most long-term economic benefit.

The Agricultural Research Service is the USDA's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.

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