Optimizing broiler performance, carcass traits, and health: evaluating thyme and/or garlic powders as natural growth promoters in antibiotic-free diets

The purpose of this study was to evaluate the effects of thyme powder (TP), garlic powder (GP), and their combination as natural alternatives to antibiotics on broiler growth performance, blood indices, and carcass characteristics. A completely randomized design was used, with four experimental groups consisting of 264 one-day-old Ross 308 broiler chicks (45.27±0.5 g). Each group received different levels of TP and GP in the diet as follows: a control group (basal diet with no additives), 2 g of GP/kg, 2 g of TP/kg, and a mixture treatment (1 g of GP/kg + 1 g of TP/kg). Each treatment included six replicates, with eleven unsexed chicks per replicate. The results showed that supplementation with TP, GP, and their combination significantly improved feed intake (FI), feed conversion ratio (FCR), and overall growth performance compared to the untreated group (UG). The different additives also significantly (P≤0.05) enhanced carcass characteristics, particularly carcass yield and heart weight, both in absolute and relative terms. Furthermore, the treatments significantly (P≤0.05) affected blood indices, leading to notable improvements in immune and antioxidant parameters, including increased levels of immunoglobulin Y (IgY), immunoglobulin M (IgM), and superoxide dismutase (SOD), as well as decreased levels of malondialdehyde (MDA), a marker of oxidative stress. These changes suggest that the supplemented groups had enhanced immunity and a better oxidative balance, contributing to improved overall health. Notably, the combined treatment of TP and GP (1% each) exhibited a synergistic effect, yielding benefits comparable to or even surpassing those of the individual TP or GP treatments. These findings support the potential of combining these natural additives to achieve a balanced improvement in growth, feed efficiency, and health status. In conclusion, supplementation with thyme powder, garlic powder, or a combination of both at appropriate levels (2% GP, 2% TP, or 1% each) can serve as an effective alternative to antibiotics, improving broiler growth performance, carcass quality, and health by enhancing immune responses and antioxidant status.