Effects of acidifier added to diets containing graded levels of crystalline tryptophan on growth performance, protein digestibility, and on brain serotonin level in broiler chickens

Abstract

The objective of the study was to investigate whether addition of acidifier (A) to a diet containing crystalline tryptophan (TRP) does not impair utilization of the amino acid both for growth and serotonin synthesis in broiler chicken. Eight groups, each of 12 eight-day-old, individually housed, female broilers, were fed on diet containing 1.57 g TRP/kg, or diets supplemented with 0.21, 0.42 and 0.63 g TRP, without or with 3 g acidifier (A - mixture of phosphoric, citric and fumaric acids) per kg. Feed intake and body weight (BW) was registered for 3 weeks, followed by balance experiment, at the end the birds were killed and digesta and brain tissue were sampled. TRP supplementation increased BW gain and improved feed utilization (P<0.05), and did not affect ileal, while slightly decreased faecal protein digestibility. The concentration of serotonin (5-HT) and the ratio of 5-hydroxy-indole-3-acetic acid (5-HIAA) to 5-HT in brain tissue increased (P<0.01) with the increase of TRP level in diet. Supplementation with A had no significant effect on performance, pH of digesta, ileal and faecal protein digestibility in comparison with unsupplemented diets. However, it lowered the concentration of 5-HT (2.75 vs 2.98 μg/g; P<0.05) and increased the ratio of 5-HIAA/5-HT (0.30 vs 0.25; P<0.01) in brain tissue, the negative effect was greatest in TRP deficient diet (TRP x A; P<0.001). It indicate for a need of careful adjusting TRP level in broiler diets supplemented with acidifiers.