Meta-analysis of growth performance indices of broiler chickens in response to turmeric (Curcuma longa L.) supplementation

Abstract

Turmeric is currently used in different poultry species for their numerous beneficial effects. The existing body of knowledge has shown variable growth performance results in broiler chickens fed turmeric (Curcuma longa L.) supplemented diets. This investigation aimed to ascertain the effect of turmeric supplementation on growth performance of broiler chickens using meta-analysis. Four online databases were used to identify studies that investigated the impact of turmeric supplementation on feed intake (FI), feed conversion ratio (FCR) and average daily gain (ADG) in broiler chickens. One hundred and forty studies were retrieved from the search conducted on the four online databases and forty studies met the inclusion criteria for the meta-analysis. The random-effects model was used for data analysis. The effect size was calculated using a standardized mean difference (SMD) with 95% confidence intervals (CI). In comparison with the controls, turmeric supplementation significantly reduced FCR (SMD = - 0.44, 95% CI −0.57 to −0.32, I2 = 88%), increased ADG (SMD = 0.44, 95% CI 0.30–0.57; I2 = 89%) and decreased daily FI (SMD = −0.12, 95% CI −0.21 to −0.04 I2 = 73%). Sub-analysis of dose-related response revealed statistically higher ADG (SMD = 0.48, 95% CI 0.33–0.62) in broiler chickens fed turmeric-supplemented diet at 0.2–11 g/kg feed. In contrast, turmeric-supplemented diet at 12 – 30 g/kg feed had no significant influence on ADG (SMD = 0.18, 95% CI −0.15 to 0.52). Significantly better FCR and ADG were recorded in broiler chickens fed turmeric-supplemented diet for 1–35 and 1–42 days, indicating that 1–35 and 1–42 days may be the optimal supplementation duration. However, there was no effect between feed intake and duration of turmeric supplementation. Birds from studies that fed turmeric-supplemented diets had improved growth performance compared to birds from studies that used turmeric extract. High heterogeneity was observed across the studies included in the meta-analysis. Meta-regression analysis found that studied covariates (supplementation level, duration of supplementation, turmeric presentation form and broiler strain) explained most of the sources of heterogeneity observed in the present meta-analysis. The mean effect size of 0.44 and 0.48 recorded for FCR and ADG, respectively suggesting that turmeric supplementation had a medium impact on growth performance indices in broiler chickens and could be used as a growth-enhancing agent. However, further research focusing on the optimal turmeric supplementation level and duration that optimize growth performance indices in broiler chickens is still needed.