Abstract
Background:
Cinnamon oil, used as a feed additive in poultry, enhances growth performance, improves antioxidant status, and augments immune response, resulting in superior meat quality and general productive efficiency.

Aim:
This study aimed to assess the effect of cinnamon oil (CO) in broiler diets on growth efficiency, hematological parameters, gene expression, and histological condition.

Methods:
Two hundred sixteen one-day-old broilers were assigned to three treatments in a fully randomized design, with each treatment subdivided into six replicates of 12 chicks. The first treatment is a control group, and the second and third are basic diets with 0.3% and 0.6% CO, respectively.

Results:
The 0.3% CO group had a higher FBW, with no significant differences (P ≥ 0.05) in BW and BWG. Birds in this group consumed less FI, leading to a notable improvement in FCR compared to the control. Additionally, 0.3% CO significantly (P ≤ 0.05) reduced total cholesterol levels without major impacts on most blood parameters, although MCH and MCHC increased in treated groups. Significant changes were observed in lipase and amylase levels, as well as higher CAT levels and lower MDA levels. Both 0.3% and 0.6% CO treatments (P ≤ 0.05) increased IGF-1, IL-10, and SOD1 levels, with the 0.6% concentration showing the highest levels. IL-1β levels remained low, indicating a specific effect of CO supplementation. Moreover, in the 0.3% CO group, CO supplementation enhanced intestinal absorption by increasing villus height and crypt depth.

Conclusion:
Adding 0.3% CO to the diet improves feed efficiency, lowers cholesterol, improves blood parameters, lowers inflammation, boosts antioxidant enzymes, and optimally improves intestinal structure, which is beneficial for poultry health and performance.

Key words: Cinnamon oil; Blood indicator; Broiler; Histology; Growth performance.