Impact of dietary tryptophan and behavioral type on behavior, plasma cortisol, and brain metabolites of young pigs1

Abstract

The behavioral reactivity in an "open-field" test and plasma cortisol levels were studied in 72 pigs from 12 litters fed for 3 wk one of three diets with different levels of tryptophan: deficient (.14%), adequate (.23%), or excess (.32%). "Open-field" tests were performed three times: 5 d (day W + 5), 23 d (day W + 23) and 45 d (day W + 45) after weaning. The exploration time and the number of grunts provided an adequate measure of the individual emotional reactivity at day W + 5. Significant correlations were obtained between exploration time and the number of grunts at each time (r = -.83 at day W + 5; r = -.46 at day W + 23; r = -.71 at day W + 45). The distinction between animals remained (P less than .05) in terms of exploration time at both 23 and 45 d after weaning. At day W + 23, exploration time was lower in the group fed the adequate diet than in the two other groups. This effect was maintained subsequently after feeding all pigs the same adequate diet (day W + 45). In 36 pigs slaughtered at day W + 23, brain TRP concentration was higher with the excess dietary TRP than with deficient or adequate levels. Conversely, other plasma amino acids (particularly threonine) accumulated only in the brains of pigs fed the deficient diet. Plasma cortisol level assayed at weaning (W) and 2 wk later increased with age and was higher in 16-h fasted (day W + 15) than in 3-h fasted (day W + 17) pigs. Correlations were observed within litters in the fasting state, between the cortisol level and behavioral traits measured at day W + 23 (r = .70 for number of grunts, r = -.60 for exploration time). Dietary TRP did not affect the plasma cortisol level irrespective of the nutritional state after weaning. However, an interaction was noted between plasma cortisol and TRP status (P less than .05). Although dietary TRP induced large variations in brain amino acids and 5-hydroxyindole concentrations, changes in behavioral and cortisol responses were relatively minor.

Effects of water supplementation with tryptophan and vitamin B6 or feeding hydrogenated fat on reducing hunger-induced drinking pre-slaughter in pigs

“…Indeed, in rats, it has been shown that vitamin B 6 supplements can stimulate serotonin synthesis in the brain (Hartvig et al 1995), especially following concomitant supplementation with vitamin B 6 and tryptophan (Lee et al 1988). In pigs, a modulation of dietary tryptophan has been shown on brain serotonin (Meunier-Salau¨n et al 1991). Nevertheless, if this was also the case in the present experiment, it had no impact on animal behaviour before slaughter.…”

Biological roles of tryptophan and its metabolism: Potential implications for pig feeding

“…In pigs, the level of tryptophan supply clearly impact on serotonin production in the brain: large excess of tryptophan increased brain serotonin concentration (Adeola and Ball, 1992) whereas tryptophan deficiency impaired serotonin production in the brain (Henry et al, 1996). In another way, Meunier-Salaun et al (1991) found lower tryptophan in plasma and brain of emotional piglets compared to non emotional piglets. Moreover, the ratio of 5-hydroxyindoleacetic acid (5-HIAA)/5-HT used as an indicator of serotoninergic activity was higher in the posterior brain of emotional piglets suggesting an increased 5-HT turnover and difference in tryptophan metabolism in the brain may be suspected.…”

“…In horses large tryptophan supply has been also proposed for its sedative effect (Grimmett and Sillence, 2005). In pigs tryptophan effects on stress response and sensitivity has been confirmed in the cases of deficiency or after the administration of large pharmacological doses of this amino acid (Koopmans et al, 2005;Guzik et al, 2006) whereas these effects remained much more discrete or inexistent for dietary supplies within nutritional ranges (Meunier-Salaun et al, 1991). For instance Koopmans et al (2005Koopmans et al ( , 2006 showed that pigs submitted to a social stress had lower plasma cortisol and noradrenaline concentrations when they were fed a large supply of tryptophan.…”

The Low Feed Intake in Newly-weaned Pigs: Problems and Possible Solutions

“…Meunier-Salaun et al (1991) have shown that brain serotonin in piglets is linearly related to dietary tryptophan level. A recent study by Koopmans et al (2006) demonstrated supplemental dietary tryptophan increased hypothalamic serotonergic activity of weanling pigs.…”