Essential Oils as a Dietary Additive for Laying Hens: Performance, Egg Quality, Antioxidant Status, and Intestinal Morphology: A Meta-Analysis

Abstract

This meta-analysis aimed to evaluate the effects of dietary supplementation with essential oils (EOs) on egg production and quality, antioxidant status in blood serum, and the intestinal morphology of laying hens. The data used were obtained from 38 peer-reviewed publications. The effect size was evaluated by weighted mean differences (WMD) between the experimental treatments (diets added with EOs) and the control treatments (diets without EOs). EO supplementation increased (p < 0.001) egg production (WMD = 2.171%), egg weight (WMD = 0.636 g), egg mass (WMD = 1.679 g/d), and decreased the feed conversion ratio (WMD = −0.074 g/g; p < 0.001). In addition, greater (p < 0.05) eggshell thickness (WMD = 14.262 mm), eggshell strength (0.080 kg/cm2), albumen height (WMD = 0.201 mm), Haugh unit (WMD = 1.102), and yolk color (WMD = 0.071) were observed in response to EO supplementation. In blood serum, the dietary inclusion of EOs increased (p < 0.05) the levels of superoxide dismutase (WMD = 1.147 U/mL), glutathione peroxidase (WMD = 879.553 U/mL), and total antioxidant capacity (WMD = 1.163 U/mL). In the duodenum, jejunum, and ileum, a higher (p < 0.05) villus height (VH), crypt depth (CD), villus width, and VH/CD ratio was observed in response to EO supplementation. In conclusion, the dietary inclusion of essential oils can be used as a nutritional strategy to improve egg production and quality, the antioxidant status of blood serum, and intestinal morphology in laying hens.