Effects of essential oil blend supplementation on growth performance, nutrient digestibility, immune response, villus...

This study examined the effects of varying essential oil (EO) blend levels on growth performance, nutrient digestibility, immune response, villus histology and cecal microbiota in Hubbard male broiler chicks. Five groups of male chicks ( $n=$ 1000) received diets with incremental EO blend levels: 0, 0.5, 1, 1.5, and 2 mL kg^-1 feed. Results showed no significant initial differences in feed intake or body weight gain. However, by week 3, the group supplemented with 2 mL kg^-1 exhibited significantly higher feed intake and weight gain ( $p<0.05$ ), sustaining these trends throughout weeks 4 and 5. The group supplemented with 2 mL kg^-1 achieved a better feed conversion ratio (FCR) in weeks 4 and 5, culminating in the most favorable overall FCR across the trial period ( $p=$ 0.04). Digestibility assessments revealed that supplementation of 2 mL kg^-1 resulted in the highest dry matter, gross energy, ether extract, and crude protein digestibility levels ( $p<0.05$ ), suggesting enhanced nutrient absorption. Immunological results indicated significantly elevated antibody titers in the group supplemented with 2 mL kg^-1 against Newcastle disease (ND), infectious bronchitis (IB), and infectious bursal disease (IBD). The group supplemented with 2 mL kg^-1 consistently achieved the highest antibody levels, notably with ND titers on day 35 ( $p=$ 0.04). These findings suggest that a 2 mL kg^-1 EO blend supplementation optimizes growth, nutrient utilization, and immune response, offering a natural alternative to promote broiler health and performance.