Meta-Analysis of Positive Effects of Dietary Turmeric (Curcuma longa L.) on Performance of Commercial Laying Hens

Turmeric improves performance in nonruminants, but results in laying hens are not consistent. This meta-analysis assessed the performance of laying hens fed turmeric powder (TP)-based diets. Nineteen studies retrieved from Google Scholar, Scopus, ScienceDirect, PubMed, and Web of Science databases were used for the meta-analysis. The outcome variables analysed were productive indices (feed intake [FI], feed conversion ratio [FCR], hen day production [HDP], egg weight [EW], egg mass [EM]), egg quality (Haugh unit [HU], shell thickness [SHT], shell strength [SHS], yolk cholesterol [YC]), serum biochemical parameters (serum cholesterol [SC], alanine transferase [ALT], and aspartate transferase [AST]), and moderator variables (layer strains, inclusion level, feeding duration, and hen's age). All analyses were performed on OpenMEE software and the R package. A random-effects model (REM) was used and results were presented as standardised mean difference (SMD) at a 95% confidence interval (CI). The results showed that dietary TP improved FCR (SMD = -0.31; 95% CI: -0.61, -0.01; p = 0.046) and HDP (SMD = 0.49; 95% CI: 0.29, 0.69; p < 0.001), but not EW, EM, HU, SHT, SHS, YC, and serum AST in layers. On the other hand, dietary TP decreased FI (SMD = -0.15; 95% CI: -0.26, -0.05; p = 0.004), SC (SMD = -75.18; 95% CI: -102.55, -47.80; p < 0.001), and ALT (SMD = -3.55; 95% CI: -4.71, -2.40; p < 0.001) in laying hens with proof of significant heterogeneity. However, meta-regression showed that layer strains and feeding duration accounted for most of the sources of heterogeneity. In conclusion, results suggest that dietary TP increased HDP and reduced FI, FCR, SC, and ALT in laying hens.