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

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 grain type and conditioning temperature during pelleting on growth performance, ruminal fermentation, meat quality and blood metabolites of fattening lambs

Ruminants can tolerate moderate concentrations of dietary tannin, making it feasible to replace corn with sorghum in ruminant diets; however, conditioning temperature of pelleted total mixed ration (PTMR) greatly affects nutrient digestibility. The objective was to determine effects of grain type and conditioning temperature during pelleting on growth performance, ruminal fermentation, meat quality and blood metabolites of fattening lambs. This was a 2 × 3 factorial study, with corn and sorghum and three conditioning temperatures (65, 75 and 85 °C) in a randomized complete design, with 36 lambs (120 ± 10.2 d and 24.9 ± 3.3 kg) grouped by weight and randomly allocated. The resulting six PTMRs were referred to as 65-S, 75-S and 85-S for sorghum-based diets, and 65-C, 75-C and 85-C for corn-based diets, for low, medium and high pelleting temperatures, respectively. There was no grain type × conditioning temperature (Grain × Temp) interaction on growth performance and apparent nutrient digestibility. Furthermore, grain type did not affect DM intake (DMI), average daily gain (ADG) or feed conversion ratio (FCR) of fattening lambs. Pelleting at 75 °C improved ADG (P < 0.03) and FCR (P < 0.02) of fattening lambs compared to other temperatures. There was a Grain × Temp interaction (P < 0.01) on ruminal pH (lowest in lambs fed 75-S). There tended (P = 0.07) to be a Grain × Temp interaction for total volatile fatty acid (VFA), and there were Grain × Temp interactions for molar proportions of acetate (P < 0.04), butyrate (P < 0.03) and branch-chained VFA (P < 0.01). Lambs fed sorghum-based PTMR had greater molar proportion of propionate (P < 0.03) and lower acetate to propionate ratio (A:P, P < 0.04). Lambs fed sorghum-based PTMR had higher plasma concentrations of urea nitrogen (N) (P < 0.03), glucose (P < 0.01) and alkaline phosphatase (P < 0.05), whereas other blood metabolites were not affected by treatments. There were Grain × Temp (P < 0.03) interactions for color coordinates of longissimus and mid-gluteal muscle. Lambs fed sorghum-based PTMR had lower (P < 0.01) dressing percentage and meat quality than those fed corn-based PTMR. We concluded that sorghum can replace corn in lamb diets without compromising growth performance and feed efficiency; furthermore, feeding sorghum vs corn improved rumen fermentation, with reduced A:P ratio and enhanced N and glucose utilization. Finally, pelleting at 75 °C increased feeding value of either sorghum- or corn-based PTMR for fattening lambs.