META-ANALYSIS OF DIETARY ESSENTIAL OILS IN BROILER NUTRITION: GROWTH PERFORMANCE, ABDOMINAL FAT AND BLOOD LIPID CHARACTERISTICS

The use of essential oils (EO) as growth promoters in modern animal production is on the rise.Studies assessing the impact of EO on growth performance and health indices, however, have produced variable results.To assess the impact of EO on feed intake (FI), feed conversion ratio (FCR), body weight gain (BWG), abdominal fat, blood levels of triglycerides, total cholesterol (TC), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) in broilers, meta-analysis approach was used.A search performed on five online databases (Google Scholar, PubMed, ScienceDirect, Scopus, and Web of Science databases) yielded 1252 studies, of which 36 were eligible for meta-analysis.Data were aggregated using Der-Simonian and Laird's random-effects model, and results were presented as mean differences (MD) at 95% confidence intervals (CI).All the statistical analyses were done in OpenMEE software.Results indicated that EO had a beneficial effect on FI (MD = 0.75 g/bird; 0.04, 1.45; P = 0.038), BWG (MD = 2.10 g/bird; 1.36, 2.84; P < 0.00) and FCR (MD = -0.06;-0.08, -0.04; P < 0.001) in broilers.In comparison with the control, dietary EO supplementation improved abdominal fat content (MD = -0.21g; -0.28, -0.13; P < 0.001), blood TC (MD = -3.85mg/dl; -5.40, -2.30; P < 0.001), HDL (MD = 5.70 mg/dl; 1.48, 9.92; P = 0.008), and LDL (MD = -7.38 mg/dl; -11.69, -3.07; P < 0.001) in broilers.However, EO supplementation did not affect blood TG (MD = -0.06;-0.08, -0.04; P < 0.001) levels in broilers.Subgroup analyses revealed that dosage, type of EO, broiler strains, and rearing phase had positive effects on measured outcomes.Meta-regression indicates that the type of EO used was a significant predictor of FI, FCR, BWG, abdominal fat, and blood TC in broilers fed EO-supplemented diets.Likewise, dosage was a significant predictor of FCR and BWG in broilers fed EO-supplemented diets.These results suggest that EO can be added to chicken diets to improve the growth performance and health status of broilers.The present meta-analysis sets guidelines for standardized experimental designs on the use of EO in broiler feeding trials in the future.