Impacts of tea tree or lemongrass essential oils supplementation on growth, immunity, carcass traits, and blood biochemical parameters of broilers reared under different stocking densities.

The effects of tea tree essential oil (TTEO) and lemongrass essential oil (LGEO) with different stocking densities on the growth performance, biochemical markers, antioxidants, and immunity state of broiler chickens were studied.  Birds were housed at stocking densities of 25, 30, 35, and 40 kg/m2. The treatments were, basal diet without any supplementation, the second and third groups were supplemented with 300 mg TTEO/kg feed, and 300 mg LGEO/kg feed, respectively. Results revealed that increasing stocking density from 25 to 40 kg/m2 significantly reduced body weight and daily weight gain at different ages. The phagocytic index and activity were significantly higher under the lower stocking density (25 kg/m2). Serum amyloid A (SAA), serum or liver transferrin (TRF), or C-reactive protein (CRP) were significant decreased when decreasing stocking density. Increasing stocking density from 25 to 40 kg/m2 resulted in a significant increase in the serum urea, creatinine, uric acid, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), malondialdehyde (MDA), and catalase (CAT) levels. However, there was a significant reduction in antioxidant enzyme activity, including glutathione peroxidase (GPx) and superoxide dismutase (SOD), as stocking density increased. The supplementation of TTEO produced significantly higher body weight and daily weight gain followed by LGEO. Additionally, the mortality rates were reduced in TTEO (27.4%) and LGEO (25%) groups. TTEO or LGEO supplementation significantly improved meat constituents and cellular immunity and reduced serum total lipids, serum and meat cholesterol, and triglycerides, SAA, TRF, and CRP. For all these measured parameters, superior results were obtained when TTEO was used compared to LGEO. TTEO or LGEO supplementation also significantly reduced serum urea, creatinine, uric acid, and the enzymatic activities of LDH, ALT, AST, MDA, and CAT (but not GPx and SOD) in comparison to the control treatment. Overall, our results showed the superiority of TTEO over LGEO as a feed supplement in broiler diets. In conclusion, TTEO treatment offers a better solution for raising broiler chickens in high stocking density.