Growth Performance, Meat Quality and Antioxidant Status of Sheep Supplemented with Tannins: A Meta-Analysis

Abstract

The objective of this study was to evaluate the effects of dietary supplementation with tannins (TANs) on productive performance, carcass characteristics, meat quality, oxidative stability, and blood serum antioxidant capacity of sheep through a meta-analysis. Using Scopus, Web of Science, ScienceDirect, and PubMed databases, a systematic search was performed for studies published in scientific journals that investigated the effects of TANs supplementation on the variables of interest. Only studies with weaned or older sheep were included. The data analyzed were extracted from 53 peer-reviewed publications. The sheep included in the present study were between 2 and 6 months old, and between 12 and 31 kg of body weight. The effects of TANs were analyzed using random-effects statistical models to examine the standardized mean difference (SMD) between treatments with TANs and control (no TANs). Heterogeneity was explored by meta-regression and a subgroup analysis was performed for covariates that were significant. Supplementation with TANs did not affect dry matter intake, pH, color (L* and b*), Warner–Bratzler shear force, cooking loss and meat chemical composition (p > 0.05). Supplementation with TANs increased daily weight gain (SMD = 0.274, p < 0.05), total antioxidant capacity (SMD = 1.120, p < 0.001), glutathione peroxidase enzyme activity (SMD = 0.801, p < 0.001) and catalase (SMD = 0.848, p < 0.001), and decreased malondialdehyde (MDA) concentration in blood serum (SMD = −0.535, p < 0.05). Supplementation with TANs decreased feed conversion rate (SMD = −0.246, p < 0.05), and the concentration of MDA (SMD = −2.020, p < 0.001) and metmyoglobin (SMD = −0.482, p < 0.05) in meat. However, meat redness (SMD = 0.365), hot carcass yield (SMD = 0.234), cold carcass yield (SMD = 0.510), backfat thickness (SMD = 0.565) and the Longissimus dorsi muscle area (SMD = 0.413) increased in response to TANs supplementation (p < 0.05). In conclusion, the addition of tannins in sheep diets improves productive performance, antioxidant status in blood serum, oxidative stability of meat and some other characteristics related to meat and carcass quality.

Effects of a Polyherbal Dietary Additive on Performance, Dietary Energetics, Carcass Traits, and Blood Metabolites of Finishing Lambs

“…Although it has previously been reported that dietary supplementation of tannin-containing plants can increase HCY and CCY [ 11 ], in this study HCW, HCY, CCW, CCY, ELC, ILC, CG, LL, and CI were similar in lambs of the different treatments. Similar responses were previously reported by Orzuna-Orzuna et al [ 5 ] in lambs supplemented with increasing doses (0, 1, 2, and 3 g kg −1 DM for 56 days) of a PA containing flavonoids, essential oils, and alkaloids; and by Lozano-Sánchez et al [ 23 ] in lambs supplemented with a PA (0, 5, 10, and 15 g kg −1 DM for 60 days) containing 12% hydrolyzable tannins.…”

“…However, the pH of the meat of lambs assigned to the PA3 treatment was between 5.5 and 5.8, which is considered normal for sheep meat [ 37 ]. In a recent study, Orzuna-Orzuna et al [ 11 ] observed that sheep meat pH decreased in response to dietary supplementation of hydrolyzable tannins. It has been reported that microbial spoilage of sheep meat increases when pH is higher than 5.8 [ 37 ].…”

“…It has been reported that dietary tannins supplementation improves the efficiency of ingested nitrogen utilization and reduces energy loss due to enteric methane emissions in sheep [ 9 ]. In addition, when added to sheep diets, tannins increase the energy intake of the diet [ 10 ] and improve the total antioxidant capacity in blood serum [ 11 ]. On the other hand, it has been reported that some plants with flavonoids increase serum growth hormone levels [ 12 ], improve immune response and antioxidant enzyme activity (catalase and superoxide dismutase) in blood serum [ 13 ], and promote muscle tissue synthesis in sheep [ 14 ].…”

Essential Oils as a Dietary Additive for Small Ruminants: A Meta-Analysis on Performance, Rumen Parameters, Serum Metabolites, and Product Quality

“…In the meta-analysis, the heterogeneity of treatment effect was assessed with the chisquare (Q) test, in which, due to its relatively low power, a significance level of p ≤ 0.10 was used [37]. In addition, the I 2 statistic was used to measure the percentage of variation due to heterogeneity [29]. Negative values of I 2 (percent variation) were assigned as zero, while values less than 25, 25 to 50, and greater than 50% indicated low, moderate, and high heterogeneity, respectively [28,29].…”

“…However, that study [27] only included six references applied to small ruminants in their database and did not evaluate productive performance, blood metabolites, or meat and milk quality. Although the meta-analytical approach has been used mainly in research related to human health, its application in research on natural food additives in domestic animals is still limited [28,29]. MA allows to combine and quantitatively synthesize previously published results from multiple independent studies [30].…”