PSII-27 Meta-analysis of the dietary inclusion of grape pomace on intake, carcass yield, and meat quality of sheep.

Abstract Grape production is one of the most important cropping activities worldwide. Thus, significant amounts of byproducts like grape pomace (GP) are utilized to feed ruminants as a source of fiber, protein, tannins, and antioxidants. Therefore, the objective of this study was to evaluate the effects of dietary inclusion of GP on intake, carcass yield, and meat quality of sheep using a meta-analytic approach. Data were collected and stratified following the PRISMA methodology. Eight manuscripts (out of 79) from 2018 to 2023 with a total of 316 sheep (26.6±4.1 kg) met the inclusion criteria to estimate the raw mean differences (RMD). The effect size was estimated by calculating the RMD between GP vs. control diets followed by a robust variance estimation and meta-regression fitting the diet characteristics like crude protein (CP), NDF content, ADF content, tannin content, and GP content in the diet (0-50%). Dietary GP did not affect (P >0.05) Dry matter intake (1.30 vs 1.32 [-0.27,0.24] kg), daily gain (280.7 vs. 230.5 [-20.7,81.1] g/d), and hot carcass weight (20.4 vs. 19.5 [-0.44,2.3] kg) compared to the control. However, dietary GP tended to increase (P = 0.09) final body weight (41.7 vs. 40.5 [-0.27, 2.8] kg) and increase (P < 0.05) cold carcass weight (21.5 vs. 19.8 [1.15-2.14] kg). Dietary GP did not affect (P >0.05) dressing % (48.9 vs. 48.7 [-2.51, -2.9] %), carcass pH (5.64 vs. 5.62[-0.03, 0.04]), and meat color a (12.7 vs. 12.5[-0.35, 1.4]), b (22.8 vs. 23.9[-2.77, 0.51]), L (38.6 vs. 38.1[-0.69,1.55]) compared to the control. However, dietary GP reduced (P=0.02) cooking loss (27.9 vs. 29.4 [-2.7, 0.29] %) and tended to reduce (P = 0.08) sheer force (37.9 vs. 43.1[-13.4,2.83] N). The variance component analyses (Ω2 and τ2) revealed a low variation between groups and comparisons for all the variables except for meat a and b color (Ω2 =7.3, 8.2) and cooking loss (τ2 = 1.2). Dietary tannins and CP strongly influenced cooking loss (R2= 0.80, cubic effect) and sheer force (R2= 0.89, cubic effect). The dose-response analysis revealed that increasing dietary tannins from GP reduced cooking loss and sheer force (P < 0.01). Results of this meta-analysis suggest that dietary GP increased meat tenderness and reduced cooking loss in sheep meat.