Kwon, W. B., J. A. Soto, and H. H. Stein. 2021. Effects of Dietary Valine, Isoleucine, and Tryptophan Supplementations to Diets Containing Excess Leucine from Corn Protein on Growth Performance of Growing Pigs. J. Anim. Sci. 99(Suppl. 1): 61–62. doi.org/10.1093/jas/skab054.103. Link to Abstract.

Kwon, Woong B., Jose A. Soto, Hans H. Stein. 2020. Effects of dietary isoleucine and valine supplementation to excess or low leucine diets on nitrogen balance and metabolism of branched-chained amino acids in growing pigs. J. Anim. Sci. 98(Suppl. 3): 33. doi.org/10.1093/jas/skaa054.059. (Abstr.). Link to abstract.

Oliveira, M. S. F., M. K. Wiltafsky, S. A. Lee, K. W. Kwon, and H. H. Stein. 2020. Concentrations of digestible and metabolizable energy and amino acid digestibility by growing pigs may be reduced by autoclaving soybean meal. Anim. Feed Sci. Technol. 114621. Link to full text.

Kwon, W. B., and H. H. Stein. 2020. Tryptophan can partially overcome negative effects of leucine in pig diets. National Hog Farmer, Online edition. Jan.

Tryptophan is an indispensable AA that is often limiting for growth in pigs fed corn-soybean meal-based diets. Tryptophan may act as a regulator of feed intake by enhancing serotonin signaling in the brain, because Trp is a precursor for serotonin. High Trp intake increases feed intake, and this is partly attributed to increased serotonin synthesis. Availability of dietary Trp in the brain is considered the rate-limiting step in hypothalamic serotonin synthesis. However, to be transported into the brain, Trp competes with other large neutral AA such as Val, Leu, Ile, Tyr, and Phe for a common transporter (L-type AA transporter 1) to cross the blood-brain barrier.

Kwon W. B., and H. H. Stein. 2019. Update on amino acids in high fiber diets: Threonine and branch chained amino acids. Midwest Swine Nutr. Conf. Indianapolis, IN, Sep. 4, 2019, p. 11-17. Link to full text

Kwon Woong B., Kevin J. Touchette, Aude Simongiovanni, Kostas Syriopoulos, Anna Wessels, Hans H. Stein. 2019. Effects of dietary leucine concentration on branched-chain amino acid metabolism in growing pigs. Journal of Animal Science, Volume 97, Issue Supplement_2, July 2019, Pages 65–66. (Abstr.). Link to abstract.

Leucine, Val, and Ile are categorized as the branched-chain AA (BCAA) because of the structural similarity of their side chains. All 3 BCAA share the enzymes that are involved in the first 2 steps of their catabolic pathway. The first step is a transamination step catalyzed by BCAA transaminase (BCAT) and producing branched-chain α-keto acids (BCKA). The second step is an irreversible degradation step catalyzed by branched-chain α-keto acid dehydrogenase (BCKDH). In the second step, Leu has been considered a key regulator as its BCKA metabolite (α-keto isocaproate) stimulates activation of the BCKDH complex in the liver. When excess Leu in diets is offered to pigs, degradation of all 3 BCAA may increase because of increased activity of BCAT and BCKDH. Leucine and Trp are both categorized as large neutral AA, and they share a common uptake pathway across the blood-brain barrier. Therefore, it is possible that excessive Leu may result in reduced Trp uptake into the brain due to competition for transporters, resulting in reduced serotonin synthesis.

Soltwedel, K. T., F. B. Sandberg, W. B. Kwon, H. H. Stein, S. J. England, M. R. Bible, T. M. Fakler, and J. Y. Jacela. 2018. Amino acid digestibility of a modified corn byproduct (Gold Pro) with and with a multi-enzyme supplement (CORE) when fed to weanling pigs. J. Anim. Sci. 96(Suppl. 2):150 (Abstr.) Link to abstract (.pdf)