Chronic increase of dietary l-tryptophan decreases gentle feather pecking behaviour

Abstract

Many studies show the involvement of the serotonergic (5-HT) system in the performance of abnormal behaviour in both human and animals. Recently, we showed that acute reduction of 5-HT turnover in the forebrain, increased gentle and severe feather pecking behaviour in chicks from a high (HFP) and low feather pecking (LFP) line of laying hens, suggesting that the performance of feather pecking behaviour involves low 5-HT neurotransmission.In the present study, we postulated that if low 5-HT is causally underlying feather pecking, increasing 5-HT turnover in the forebrain will decrease the development and performance of feather pecking. Augmentation of 5-HT neurotransmission in the brain was induced by chronically increasing dietary levels of the essential amino acid l-tryptophan (TRP) from which 5-HT is synthesised. From the age of 34 days, LFP and HFP chicks were fed a diet containing 2% TRP, whereas control birds of both lines were continuously fed with the normal rearing feed (0.16% TRP). From 35 days of age, litter was removed from the pens (10 pens/line-treatment) and all chicks (10 chicks/pen) were housed on a slatted floor until the end of the experiment. At 49 days of age, feather pecking behaviour was studied for 30 min. At 50 days of age baseline corticosterone, TRP and other large amino acids (LNAAs) were measured in the blood plasma of decapitated chicks (10 chicks per line-treatment). Furthermore, plasma corticosterone and central 5-HT turnover levels in response to manual restraint (5 min) were determined (10 chicks/line-treatment).For neither gentle nor severe feather pecking a significant line × treatment interaction was found. However, TRP treatment resulted in a significant [P = 0.02] overall decrease of the frequency of gentle feather pecking. For severe feather pecking a similar but not significant pattern was found. Significant line effects were found for gentle and severe feather pecking. HFP birds showed significantly higher levels of gentle and severe feather pecking behaviour than LFP birds [P < 0.001]. TRP treatment significantly increased the TRP/LNAA ratio in the plasma of the chicks. Furthermore, TRP treatment overall increased baseline and stress-induced levels of plasma corticosterone (although * Corresponding author. Tel.: +31-320-238171; fax: +31-320-239094. van Hierden et al. / Applied Animal Behaviour Science 89 (2004) [71][72][73][74][75][76][77][78][79][80][81][82][83][84] more pronounced in the LFP line). TRP supplementation significantly increased 5-HT turnover in the hippocampus and archistriatum and tended to do so in the remainder of the forebrain.The results confirm our hypothesis that feather pecking behaviour is triggered by low serotonergic neurotransmission, as increasing serotonergic tone, by increasing dietary TRP, decreases gentle feather pecking behaviour.

Across-Line SNP Association Study for Direct and Associative Effects on Feather Damage in Laying Hens

“…They suggest that detecting the same genetic markers in different populations implies that they are close to the functional mutation, which agrees with the theory of across-line association studies (Biscarini et al 2010). Therefore feather pecking in laying hens can seemingly be controlled by modulating their serotonergic system, by means of genetic selection or husbandry practices, either pharmacologically or dietary (van Hierden et al 2004a). Interestingly, the recent study by Bolhuis et al (2009) shows that genetic selection for low mortality, using the social models, leads to changes in the serotonergic system, already in the second generation of selection.…”

“…Substantial scientific evidence of the role of the serotonergic system in the development and modulation of feather pecking behaviour in laying hens has accrued over the last years (van Hierden et al 2002(van Hierden et al , 2004aBolhuis et al 2009). These studies related the occurrence of feather pecking with serotonin concentration and activity either in the brain or peripherally (circulatory system or peripheral nervous system), predominantly suggesting that lower levels of serotonin are associated with predisposition to perform feather pecking (van Hierden et al 2004a, b;Bolhuis et al 2009).…”

“…Most of the evidence point at the redirected ground pecking theory (Huber-Eicher and Wechsler 1997), with active or even hyperactive birds having the highest risk of developing FP (Newberry et al 2007;Kjaer 2009). The serotonergic system has been shown to play an important role in the modulation of FP (van Hierden et al 2002(van Hierden et al , 2004a Edited by Stephen Clark Maxson.…”

Feather Pecking in Laying Hens: Environmental and Endogenous Factors

“…Savory et al (1999) and v a n Hierden et al (2004b) found reduced feather pecking damage after L-tryptophan dietary supplementation, while diet with increased level of methionine and cystine did not have any significant effects on FP (Kjaer and Sörensen 2002). Increasing protein level in the diet had a positive effect on plumage and lowered FP and cannibalism.…”

Supplemental dietary tryptophan modifies behavior, concentrations of salivary cortisol, plasma epinephrine, norepinephrine and hypothalamic 5-hydroxytryptamine in weaning piglets

“…Tryptophan has already been proved to alleviate depression and aggression in humans (Mendelsohn et al, 2009) and animals. It has been shown that the supplementation of tryptophan may reduce aggression and alleviate stress in many species such as pigs (Henry et al, 1996;Koopmans et al, 2005Koopmans et al, , 2006Poletto et al, 2010;S eve et al, 1991) and chickens (Laycock and Ball, 1990;Rosebrough, 1996;Shea-Moore et al, 1996;Van Hierden et al, 2004). Tryptophan crosses the blood-brainbarrier via transporter proteins and acts as the precursor for 5-hydroxytryptamine (5-HT) synthesis in the serotonergic neurons.…”