Effect of Tryptophan Supplementation in Protein Deficient Diets on Performance, Gut Development and Immune Responses in Broiler Chickens

The current trial was conducted to investigate effects of tryptophan (Trp) supplementation in crude protein (CP) deficient diets on performance, gut development and immune responses in broiler chickens. A total of 420 day-old broiler chicks (Ross 308) were assigned to one of 6 dietary treatments, ‎comprising 5 replicates in a completely randomized design including: 1) ‎control diet (CTL) (diet based on Ross 2014 recommendation), 2) CTL + 0.15% Trp (+Trp), 3) low CP diet 1 (LCP1) (10% CP lower than Ross 2014 recommendation), 4) LCP1 + 0.15% Trp, 5) low CP diet 2 (LCP2) (20% lower CP than Ross 2014 recommendation), and 6) LCP2 + 0.15% Trp. Body weight (BW), ‎daily feed intake and feed ‎conversion ratios were evaluated in different phases of the experiment. Digestive organs were measured on day 28 and at the end of the rearing period. Morphology of small intestine was evaluated on day 28 of age. The tonic immobility test was applied at the end of the experiment. Birds receiving low CP diets had lower BW and daily weight gain (DWG) during the starter period (P