Effect of different levels of tryptophan on productive performance, egg quality, blood biochemistry, and caecal microbiota of hens housed in enriched colony cages under commercial stocking density

A study was conducted to determine the tryptophan (Trp) requirement of brown hens housed in enriched colony cages. A corn and wheat-based diets with 8 levels of standardized ileal digestible (SID) Trp (0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, and 0.31% of the diet) were manufactured. The diet containing SID Trp 0.10% had no supplemental Trp and was treated as control. A total of 1,344 hens were randomly allocated to 8 treatments, each having 8 replicate cages with 21 hens per cage. Body weight gain (BWG), egg production (EP), feed conversion ratio (FCR), egg quality, blood biochemistry, caecal microbial profile, and concentration of indoles were determined over a period of 16 wk. The EP was linearly improved by supplementing diet with Trp and was highest in 0.25% SID-Trp group compared to control. Trp supplementation improved (P < 0.05) FCR, overall BWG, egg shell characteristics compared to control. The microbial shift in the caecum in response to Trp supplementation was significant in response to higher than current recommendations (0.22% of SID Trp) and indicated a microbial shift towards beneficial bacteria. Indole and skatole concentrations were only significantly different (P < 0.05) when hens in control group were compared with those containing highest levels of SID-Trp. This study demonstrates that when hens are at its peak production and are reared in enriched colony cages their Trp requirement is higher than current National Research Council (1994) recommendations and 0.22% of the SID-Trp in diet can be considered as an optimal level based on regression analysis.