Dietary gamma-oryzanol and vitamin E tocotrienols mitigate the negative impacts in laying hens reared under high stocking density

A completely randomized experiment with a 2 × 2 × 2 factorial arrangement of treatments was used to evaluate the effect of stocking density (low, 840 cm²/hen vs. high, 420 cm²/hen) and addition of 200 ppm gamma-oryzanol (GO), 200 ppm vitamin E tocotrienols (VE), or both on productivity, egg quality, and immune- and health-related mRNA abundance. Compared with laying hens housed at low stocking density, high stocking density during 54–62 weeks of age resulted in a significantly lower average daily feed intake and hen-day egg production. The supplementation of VE in the diet increased average egg weight and egg mass significantly (p < 0.05). However, improved feed conversion ratio and higher egg mass were detected in laying hens fed dietary GO (p < 0.05). A significant interaction of VE by GO supplementation on feed conversion ratio (p < 0.05) was observed. This was accompanied by an improved feed conversion ratio in laying hens reared under high stocking density. Except for eggshell breaking strength (p < 0.05), there was no main effect of dietary VE, GO and stocking density on any other egg quality parameters examined. This was associated with decreased eggshell breaking strength in laying hens reared under high stocking density, while eggshell hardness improved in hens fed dietary VE and GO. Among hens kept on a high stocking density, there was a decrease in 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) mRNA abundance in the VE group, while the highest interferon gamma (IFN-γ) mRNA abundance was detected in hens fed the GO diet (p < 0.05). Thus, the data suggested that dietary GO or VE at a level of 200 ppm, either individually or in combination, can improve egg productivity and eggshell hardness as well as regulate mRNA abundance of immune- and stress-related genes. We conclude that these dietary antioxidants should be part of a nutritional strategy to mitigate the negative impacts on laying hens reared under high stocking density conditions.