Because of its high content of polyphenolic compounds, the dietary inclusion of grape pomace (GP) in ruminant diets can reduce reactive nitrogen (N) and methane emissions and enhance the shelf life and beneficial fatty acids (FAs) content of meat. However, the dietary inclusion of GP beyond a threshold that is still to be determined for feedlot cattle can also compromise nutrient supply and, thus, growth performance. This study investigated the optimum proportion of GP in finishing cattle diets. Nutrient intake and apparent total tract digestion, ruminal pH and fermentation, estimated microbial protein synthesis, route of N excretion, and blood metabolites were measured. Six ruminally fistulated crossbred beef heifers (mean initial body weight ± SD: 714 ± 50.7 kg) were used in a replicated 3 × 3 Latin square with 21-d periods. Dietary treatments were 0%, 15%, and 30% of dietary dry matter (DM) as GP, with diets containing 84%, 69%, and 54% dry-rolled barley grain, respectively. There was a linear increase (P = 0.07) in DM intake and quadratic change (P ≤ 0.01) in neutral detergent fiber (NDF) intake. There was a quadratic change (P ≤ 0.04) in apparent total tract DM, NDF, and crude protein digestibility as dietary GP content increased. However, there were no treatment effects (P ≥ 0.18) on total ruminal short-chain FA concentration and duration and area pH < 6.2, 5.8, and 5.5. Although N intake did not differ (269, 262, 253 g/d; P = 0.33) across dietary treatments, feeding GP led to a tendency for a quadratic change (P ≤ 0.07) in ruminal ammonia-N and plasma urea-N concentrations. Total N excretion also changed (quadratic, P = 0.03) because of changes (quadratic, P = 0.02) in fecal N excretion as urinary excretion of N and urea-N did not differ (P ≥ 0.15) across treatments. Feeding GP led to quadratic changes (P ≤ 0.01) in fecal excretion of fiber-bound N. Microbial N flow and apparent N retention also changed (quadratic, P ≤ 0.04) as dietary GP proportion increased. In conclusion, responses to dietary GP proportion were mostly quadratic with indications that nutrient supply as reflected by changes in apparent total tract nutrient digestibility, microbial N supply, and apparent N retention could be compromised beyond a 15% dietary inclusion level.

中文翻译：

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饲养场牛日粮中葡萄渣的最佳比例：瘤胃发酵、全肠道养分消化率、氮利用和血液代谢物

由于其多酚类化合物含量高，在反刍动物日粮中添加葡萄渣 (GP) 可以减少活性氮 (N) 和甲烷排放，并提高肉类的保质期和有益脂肪酸 (FAs) 含量。然而，超过对饲养场牛的阈值的 GP 日粮添加量也会影响营养供应，从而影响生长性能。本研究调查了 GP 在肥育牛日粮中的最佳比例。测量了营养摄入和表观全道消化、瘤胃 pH 值和发酵、估计的微生物蛋白质合成、N 排泄途径和血液代谢物。6 头瘤胃瘘管杂交小母牛（平均初始体重 ± SD：714 ± 50.7 kg）被用于重复的 3 × 3 拉丁方阵，周期为 21 天。日粮处理分别为 0%、15% 和 30% 的日粮干物质 (DM) 作为 GP，日粮分别含有 84%、69% 和 54% 的干轧大麦粒。DM 摄入量呈线性增加 (P = 0.07)，中性洗涤纤维 (NDF) 摄入量呈二次变化 (P ≤ 0.01)。随着日粮 GP 含量的增加，表观全肠道 DM、NDF 和粗蛋白消化率呈二次变化（P ≤ 0.04）。然而，处理对瘤胃总短链 FA 浓度和持续时间以及面积 pH < < 0.18 没有影响（P ≥ 0.18）。6.2、5.8 和 5.5。尽管不同日粮处理的 N 摄入量没有差异（269、262、253 g/d；P = 0.33），但饲喂 GP 导致瘤胃氨氮和血浆尿素 N 浓度呈二次变化趋势（P ≤ 0.07） . 由于变化（二次，P = 0.02) 在粪便 N 排泄中，因为 N 和尿素-N 的尿排泄在治疗之间没有差异 (P ≥ 0.15)。饲喂 GP 导致粪便中纤维结合氮的排泄量呈二次变化（P ≤ 0.01）。随着日粮 GP 比例的增加，微生物 N 流量和表观 N 保留也发生变化（二次，P ≤ 0.04）。总之，对日粮 GP 比例的反应大多是二次方的，表明在 15% 的日粮添加水平以上时，表观全肠道养分消化率、微生物氮供应和表观氮保留的变化所反映的养分供应可能会受到影响。P ≤ 0.04) 随着日粮 GP 比例的增加。总之，对日粮 GP 比例的反应大多是二次方的，表明在 15% 的日粮添加水平以上，营养供应（如表观全肠道养分消化率、微生物氮供应和表观氮保留的变化所反映）可能会受到影响。P ≤ 0.04) 随着日粮 GP 比例的增加。总之，对日粮 GP 比例的反应大多是二次方的，表明在 15% 的日粮添加水平以上，营养供应（如表观全肠道养分消化率、微生物氮供应和表观氮保留的变化所反映）可能会受到影响。