Tryptophan is an essential amino acid which plays a crucial role in protein biosynthesis and is absorbed into the body and transformed into a series of bioactive compounds and secondary metabolites. Some of the most important compounds include 5-HTP, serotonin, melatonin, kynurenine, and niacin.
Serotonin is involved in emotional regulation, behavior management, and sleep cycle maintenance. Melatonin can affect circadian rhythm, mood, sleep, etc. Tryptophan's ability to produce serotonin and melatonin is why it is commonly given to dogs, horses and other animals to reduce anxiety, stress and aggressive behavior.
Although tryptophan is widely known in the veterinary community for this application in mammals, studies have demonstrated similar effects in chickens. M Shea et al found that dominant male roosters were less aggressive towards subordinate roosters in the flock. It helped reduce excessive feather pecking behavior in hens in studies by T Van Hieu et al (2022), Yildirim et al (2020), Birkl et al (2019a), Birkl et al (2019b) and Khattak and Helmbrecht (2019).
Tryptophan can improve immunity since melatonin stimulates the development of immune cells (Chen et al., 2016; Guo et al., 2015; Moore & Siopes, 2000) and promotes the growth of beneficial bacteria (Bifidobacterium and Lactobacillus) and inhibits the growth of pathogenic bacteria such as Escherichia coli, Clostridia, Enterobacteria, and Campylobacter.
Tryptophan comes as a white powder with a flat taste and can be purchased over the counter without a prescription. It is naturally found in certain foods. Foods naturally high in tryptophan include pumpkin and sesame seeds, eggs and tofu.
Poultry Specific Studies
| Type | Plant Part | Dosage | Specific use | Results | Ref |
|---|
| Chickens | | 0.2% diet | improved gut microbiota | the results indicated that dietary tryptophan alleviates intestinal inflammatory damage caused by long photoperiod via the inhibition of Nucleotide-Binding Oligomerization Domain, Leucine-Rich Repeat and Pyrin Domain-Containing 3 inflammasome activation, which was mediated by tryptophan metabolites. | D Ma et al., 2024 |
| Chickens | | 10% diet | immune system | The diets containing tryptophan had a significant effect on the number of blood lymphocytes, so that the addition of 10% tryptophan increased the blood lymphocytes. The addition of 10% tryptophan level increased the immunity of chickens against HI antibody. | K Parsaeimehr et al., 2022 |
| Chickens | | 100 mg/kg bw | reduce the harmful effects of OTA on the intestinal mucosa | treatment with L-tryptophan can neutralize the effects on intestinal morphology, the levels of antibodies, and IgA+ cells in the gut of intoxicated chicks, suggesting that treatment with L-tryptophan may be a valid alternative mean to reduce the harmful effects of Ochratoxin A on the intestinal mucosa. | F Ricci et al., 2021 |
| Chickens | | 0.22-0.62% diet | gut microbiota | Increased Enterococci, and Bifidobacteria populations, while E. coli, Clostridia, Campylobacter and Enterobacteria populations decreased in the chickens' gut microbiota when they were on their way to the slaughterhouse to be tortured and killed. | A Bello et al., 2017 |
| Ducks | | 0.18-1.08% diet | Stress reduction | Was found to alleviate stress and improve growth performance, antioxidative activity, stress and improve growth performance, antioxidative activity in ducks living in overcrowded, unsanitary environments. | Y Liu et al., 2015 |
| Chickens | | 21 g TRP/kg diet | | Adding tryptophan significantly reduced gentle feather pecking behavior and increased the duration of feeding behavior. | Y van Hierden et al., 2004 |
| Chickens | | 0.4% diet | fear reduction | May have a mild fear-reducing effect. | R Newberry et al., 1993 |
| Chickens | | 0.75-1.5% diet | decreased aggression | A significant interaction was found between dominance status and supplemental TRP for aggression, with TRP decreasing pecking more in dominant than subordinate birds. In Experiment 1, there were positive correlations (p < 0.05) between body weight and dominance status in both the control and 0.75% TRP group (p < 0.05) and no correlation in the 1.5% TRP group. The decrease in aggression by dominant males may have allowed subordinate birds to gain greater access to the feed. The results indicate that dominant and subordinate males show a differential sensitivity to the effects of dietary TRP, with TRP decreasing pecking more in dominant birds. | M Shea et al., 1991 |
References
- Seo, Su-Kil, and Byungsuk Kwon. "Immune regulation through tryptophan metabolism" Experimental & Molecular Medicine 55.7 (2023)
- Henry, Maggie, et al.. "Effect of varying levels of Dietary Tryptophan on Aggression and abnormal behavior in growing Pigs" Frontiers in Veterinary Science 9 (2022)
- Fouad, Ahmed Mohamed, et al.. "Tryptophan in poultry nutrition: Impacts and mechanisms of action" Journal of animal physiology and animal nutrition 105.6 (2021)
- Linh, Nguyen Thuy, Budi Guntoro, and Nguyen Hoang Qui. . "Immunomodulatory, behavioral, and nutritional response of tryptophan application on poultry." Veterinary World 14.8 (2021)
- Hao, E. Y., Chen, H., Wang, D. H., Huang, C. X., Tong, Y. G., Chen, Y. F., Zhou, R. Y., & Huang, R. L.. "Melatonin regulates the ovarian function and enhances follicle growth in aging laying hens via activating the mammalian target of rapamycin pathway." Poultry Science, 99(4), 2185–2195. (2020)
- Mund, Muhammad D., et al.. "Effect of dietary tryptophan supplementation on growth performance, immune response and anti?oxidant status of broiler chickens from 7 to 21 days" Veterinary Medicine and Science 6.1 ( (2020)
- Goo, D., Kim, J. H., Park, G. H., Delos Reyes, J. B., & Kil, D. Y. "Effect of stocking density and dietary tryptophan on growth performance and intestinal barrier function in broiler chickens" Poultry Science, 98(10), 4504–4508. (2019)
- Birkl, P., Chow, J., McBride, P., Kjaer, J. B., Kunze, W. A., Forsythe, P., & Harlander, A.. "Effects of acute tryptophan depletion on repetitive behavior in laying hens." Frontiers in Veterinary Science, 6, 230–237 (2019)
- Khattak, F., & Helmbrecht, A. "Effect of different levels of tryptophan on productive performance, egg quality, blood biochemistry, and caecal microbiota of hens housed in enriched colony cages under commercial stocking density." Poultry Science, 98(5), 2094–2104 (2019)
- Goo, D., et al.. "Effect of stocking density and dietary tryptophan on growth performance and intestinal barrier function in broiler chickens" Poultry science 98.10 (2019)
- Li, J., Li, R. X., Liu, G., Lv, C. F., Mi, Y. L., & Zhang, C. Q. . "Effect of melatonin on renewal of chicken small intestinal mucosa" Poultry Science, 96(8), 2942–2949 (2017)
- Chen, F., Reheman, A., Cao, J., Wang, Z., Dong, Y., Zhang, Y., & Chen, Y. "Effect of melatonin on monochromatic light-induced T-lymphocyte proliferation in the thymus of chickens." Journal of Photochemistry and Photobiology B: Biology, 161, 9–16 (2016)
- Guo, Q., Dong, Y., Cao, J., Wang, Z., Zhang, Z., & Chen, Y. "Developmental changes of melatonin receptor expression in the spleen of the chicken, Gallus domesticus" Acta Histochema, 117(6), 559–565 (2015)
- Dong, X. Y., Azzam, M. M. M., Rao, W., Yu, D. Y., & Zou, X. T. "Evaluating the impact of excess dietary tryptophan on laying performance and immune function of laying hens reared under hot and humid summer conditions." British Poultry Science, 53(4), 491–496 (2012)
- Morandini, Leonel, et al.. "Dietary L-tryptophan modulates agonistic behavior and brain serotonin in male dyadic contests of a cichlid fish" Journal of Comparative Physiology A 205 (2009)
- Moneva, P., et al.. "Study on the metabolic implication of supplemental tryptophan in exposed to stress chickens" Bulgarian Journal of Agricultural Science 14.4 (2008)
- DeNapoli, Jean S., et al.. "Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs" Journal of the American Veterinary Medical Association 217.4 (2000)
- Moore, C. B., and T. D. Siopes.. "Effects of lighting conditions and melatonin supplementation on the cellular and humoral immune responses in Japanese quail Coturnix coturnix japonica" General and Comparative Endocrinology 119.1 (2000)
- SHEA-MOORE, MARGARET M., OWEN P. THOMAS, and JOY A. MENCH.. "Decreases in aggression in tryptophan-supplemented broiler breeder males are not due to increases in blood niacin levels" Poultry science 75.3 (1996)
- DeNapoli, Jean S., et al.. "The interaction of dominance status and supplemental tryptophan on aggression in Gallus domesticus males" Pharmacology Biochemistry and Behavior 38.3 (1991)
- Shea, M. M., J. A. Mench, and O. P. Thomas.. "The effect of dietary tryptophan on aggressive behavior in developing and mature broiler breeder males" Poultry Science 69.10 (1990)
