Effect of different levels of tryptophan on laying performance, egg quality, blood and tibia parameters, and feather damage of laying hens in barn system

Abstract

Animal welfare is a priority in the laying hen industry, with feather pecking being a major issue to address challenge. Feather pecking is a behavior derived from exploration and involves gently pecking the feathers of other hens. However, when pecking becomes severe, such as pecking or eating the feathers or tissues of others, it can lead to stress, decreased productivity, and even mortality. Studies have reported on a variety of methods to control these behaviors including nutrition, facilities, and management. L-tryptophan (TRP) is one of the essential amino acids and is a precursor to serotonin, a neurotransmitter known to control stress, aggression, and mood. The objective of this study was to investigate the effects of different supplementation levels of TRP on egg performance, stress parameters of blood, and welfare indices in laying hens. A total of 700 Hy-Line Brown layer, aged 70 weeks, were randomly assigned to four treatment groups. Each group fed a basal diet, based on maize and soybean meal, supplemented with 0.0 %, 0.25 %, 1.0 %, and 2.0 % TRP for 4 weeks. The addition of 0.25 and 1.0 % TRP were improved the hen-day egg production and egg mass compared to control group. Also, the level of corticosterone and serotonin in serum were positively affected by the 1.0 % TRP supplementation. Hens fed a diet with 1.0 % TRP resulted lower feather damage score than control. Furthermore, eggshell thickness improved with the addition of TRP to the diet. In conclusion, our findings suggest that supplementation with 1.0 % TRP may mitigate stress and improve egg production and welfare indices of laying hens in barn system