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United States Department of Agriculture

Agricultural Research Service

Title: Supplemental L-Tryptophan Effects on Serotonin, Cortisol, Intestinal Integrity, and Behaviour in Weanling Piglets

Authors
item Koopmans, S - ASG, WAGENINGEN, UR
item Guzik, A - LOUISIANA STATE UNIVERSIT
item Van Der Meulen, J - ASG, WAGENINGEN, UR
item Dekker, R - ASG, WAGENINGEN, UR
item Kogut, J - ASG, WAGENINGEN, UR
item Kerr, Brian
item Southern, L - LOUISIANA STATE UNIVERSIT

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 2005
Publication Date: January 5, 2006
Citation: Koopmans, S.J., Guzik, A.C., Van Der Meulen, J., Dekker, R., Kogut, J., Kerr, B.J., Southern, L.L. 2006. Supplemental l-tryptophan effects on serotonin, cortisol, intestinal integrity, and behaviour in weanling piglets. Journal of Animal Science. 84:963-971.

Interpretive Summary: Weaning and subsequent mixing of nursery pigs induces aggression and stress, which is commonly known to have a negative impact on feed intake, growth, and gastrointestinal health. Stress that is involved in mixing pigs is assumed to affect endocrinology, physiology, and metabolism which results in changes in the body’s homeostasis. A relief of the negative aspects of stress after weaning and mixing may be obtained by dietary measures. It has been shown that the dietary amino acid tryptophan may reduce aggression and alleviate stress in many species such as pigs, rats, and chickens. As such, dietary tryptophan may improve animal welfare and overall performance of piglets after weaning and mixing. Tryptophan has been shown to affect brain and nervous system functioning through interference with serotonerigic neurotransmission. Tryptophan serves as the immediate precursor for serotonin synthesis and tryptophan-induced serotoninergic activity in the brain has been implicated in the regulation of many behavioural and physiological processes such as mood, aggression, stress susceptibility, sleep patterns, and feed intake. In theory, increased levels of tryptophan would elevate brain serotonin concentration and reduce stress susceptibility. If dietary tryptophan is able to reduce stress it may therefore increase feed intake, gastrointestinal integrity, and overall performance in nursery pigs. The aim of the present study was to investigate the effects of supplemental dietary L-tryptophan (5 g/kg feed) on behaviour, neuroendocrinology, intestinal integrity, and growth performance in nursery pigs subsequent to weaning and mixing. Data from these experiments indicate that supplemental tryptophan reduces stress through increased serotonergic activity and decreased salivary cortisol at mixing. The increased intestinal villus height and increased villus to crypt ratio and the lack of affect on intestinal transport of macro molecules show that tryptophan improves intestinal morphology without affecting intestinal permeability. Pig performance was not affected by tryptophan supplementation. Research results described in this report provides nutritionists at universities, feed companies, allied industries, and swine production facilities data showing that diets containing high tryptophan levels may be helpful in increasing welfare and gastrointestinal robustness in nursery pigs during specific periods of increased stress such as weaning and mixing. However, prolonged feeding of a sufficient amount of tryptophan may be necessary to detect unequivocal effects on stress, gastrointestinal integrity, and growth performance.

Technical Abstract: Stress occurs in intensive pig farming when piglets are weaned and mixed. This stress may be reduced with elevated dietary levels of tryptophan (TRP). In this study, we investigated the effects of supplemental dietary L-TRP (5 g/kg feed) on neuroendocrinology, intestinal integrity, behaviour and growth performance in nursery pigs before and after mixing. Mixing occurred 5 d post-weaning and diet introduction. Around mixing, TRP fed pigs versus control pigs showed approximately a two-fold elevation in plasma TRP concentrations (68 ± 7 versus 32 ± 2 'mol/L, P < 0.001), a 38% increase in hypothalamic serotonin turnover as measured by 5-HIAA:5-HT (P < 0.0001) and an 11-18% increase (P < 0.05) in the intestinal villus-height to crypt-depth ratio. On the day of mixing, saliva but not plasma cortisol concentrations were approximately two-fold reduced (1.0 ± 0.1 versus 1.9 ± 0.5 ng/mL, P < 0.02) in TRP fed pigs versus control pigs, respectively. Intestinal permeability, both paracellular (HRP) and transcellular (FITC) transport of macromolecules were not affected by dietary treatment but mixing induced a 2-fold reduction (P < 0.01) in transcellular transport. Behavioural responses, lying and standing, at mixing were not affected by dietary treatment except for d 10 post diet introduction where TRP supplementation induced more lying and less standing (P < 0.02). Average daily gain and feed intake were similar among dietary groups. In conclusion, supplemental dietary TRP (5 g/kg) to piglets increased hypothalamic serotonergic activity, reduced the saliva cortisol response to mixing, improved intestinal morphology and reduced physical activity ten days post-diet introduction. Consequently, diets containing high TRP levels may be helpful in increasing welfare and gastrointestinal robustness in nursery pigs during specific periods of increased stress such as weaning and mixing.

Last Modified: 11/27/2014
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