Effects of tannins supplementation to sheep diets on their performance, carcass parameters and meat fatty acid profile: A meta-analysis study
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This study was carried to evaluate the effects of tannins supplementation to sheep diets on their performance, carcass parameters and meat fatty acid profile through meta-analysis. Seventy-four peer-reviewed publications with 183 treatment means were included in the data set. The effects of tannins as an additive in sheep diets were evaluated by examining the weighted mean difference (WMD) between tannins treatment (diets with tannins inclusion) and control treatment (diets with no tannins). Heterogeneity was explored by meta-regression and subgroup analysis performed for: genetic group; animal age; tannins supplementation period, experimental design; amount of condensed tannins and concentrate in diet. Based on our results, tannins should not be fed to lamb younger than 3 months of age due to their negative effect on carcass weight. Enteric methane emissions (CH4 g/kg DMI) reduced by 17.5 % with tannins supplementation. Tannins supplementation also altered N metabolism by increasing N intake (2.10 %), retained N (5.44 %) and fecal N excretion (2.99 %) and reducing urinary N excretion (9.7 %). Nevertheless, the effects of tannins feeding on N metabolism varied according to the experimental design used (rotative vs. continuos). Therefore, the use of rotative experimental design in studies carried to evaluate the response of sheep to tannins can result in responses with confounded error due to the possibility of having residual effects of treatments. Increased meat concentrations of fatty acid with human health benefits were reported with tannins supplementation. Concentrations of eicosapentaenoic acid (EPA C20:5 ω-3; 26.63 %), docosapentaenoic (DPA C22:5 ω-3; 12.08 %), docosahexaenoic (DHA C22:6 ω-3; 10.59 %) and total omega-3 (14.01 %) were all higher in meat from sheep fed tannins compared to those fed control diet (diets with no tannins). Additionally, condensed tannins inclusion to sheep diets in amounts ranging from 20.0 to 25.0 g/kg of DM increased meat concentrations of arachidonic acid, EPA C20:5 ω-3, DPA C22:5 ω-3, DHA C22:6 ω-3, total PUFA, total omega-3 and total omega-6.