Abstract Objectives were to evaluate the effects of cattle breed, Holstein or Angus, and corn processing methods on total tract digestibility, and ruminal pH and volatile fatty acid concentrations (VFA). Six Holstein (BW = 548 ± 6.3 kg) and 6 Angus steers (BW = 596 ± 7.6 kg) previously fitted with rumen cannulae, were assigned to a 2 × 3 factorial arrangement of treatments. Factors included breed, Holstein or Angus, and corn processing method, whole shelled corn (WSC), dry rolled corn (DRC), or finely ground corn (FGC). Steers were fed diets containing 815 g/kg corn grain, 100 g/kg grass hay, 65 g/kg soybean, and 20 g/kg supplement. Steers were fed in a replicated 3 × 3 Latin square split-plot design. Each period consisted of 14 d diet adaptation followed by 7 d of sample collection. On d 1, rumen contents were collected. Ruminal pH was recorded at 0, 3, 6, 12, and 18 h after feeding and a portion of the strained ruminal fluid was subsampled at 0 and 3 h for VFA analysis. From d 2–7, feces, feed, and refusals samples were collected and analyzed for DM, NDF, and starch. Data were analyzed using the MIXED procedures in SAS (v9.4 SAS Inst. Inc., Cary, NC). Repeated measures were used to analyze changes in ruminal pH and VFA over time. There was no interaction of breed × diet (P ≥ 0.16) on diet intake and digestibility. Holstein steers had a greater (P ≤ 0.05) intake than Angus steers, regardless of diet. There was no effect (P ≥ 0.81) of breed on diet digestibility. Digestibility of DM, OM, and starch were reduced (P ≤ 0.03) when corn grain was fed whole, regardless of breed. There was an interaction of breed × diet (P = 0.02) on ruminal pH. Angus steers fed FGC had the most acidic ruminal pH, while ruminal pH in Holstein steers fed FGC was similar to ruminal pH Holstein steers fed WSC or DRC. There was no interaction of breed × diet (P = 0.28), nor were there main effects of breed (P = 0.21) or diet (P = 0.92), on total VFA concentrations. Although Holstein steers ate 22 % more DM than Angus steers, they were able to sustain a greater (P = 0.04) ruminal pH. Compared to feeding WSC, starch digestibility improved by 5% when processed corn grain was fed, regardless processing method.

中文翻译：

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牛品种和玉米加工对瘤胃 pH 值和挥发性脂肪酸浓度以及表观消化率的影响

摘要 目的是评估牛品种、荷斯坦牛或安格斯牛以及玉米加工方法对总消化道消化率、瘤胃 pH 值和挥发性脂肪酸浓度 (VFA) 的影响。六头荷斯坦牛 (BW = 548 ± 6.3 kg) 和 6 头安格斯阉牛 (BW = 596 ± 7.6 kg) 之前装有瘤胃插管，被分配到 2 × 3 因子处理安排。因素包括品种、荷斯坦或安格斯以及玉米加工方法、全去壳玉米 (WSC)、干轧玉米 (DRC) 或细磨玉米 (FGC)。给公牛饲喂含有 815 g/kg 玉米粒、100 g/kg 干草、65 g/kg 大豆和 20 g/kg 补充剂的日粮。用重复的 3 × 3 拉丁方裂区设计喂养阉牛。每个时期包括 14 天的饮食适应，然后是 7 天的样品收集。在第 1 天，收集瘤胃内容物。在饲喂后 0、3、6、12 和 18 小时记录瘤胃 pH 值，并在 0 和 3 小时对部分滤过的瘤胃液进行二次取样用于 VFA 分析。从第 2 天到第 7 天，收集粪便、饲料和拒绝样品并分析 DM、NDF 和淀粉。使用 SAS (v9.4 SAS Inst. Inc., Cary, NC) 中的 MIXED 程序分析数据。重复测量用于分析瘤胃 pH 值和 VFA 随时间的变化。品种×日粮（P≥0.16）对日粮摄入量和消化率没有交互作用。无论饮食如何，荷斯坦公牛的摄入量均高于安格斯公牛（P ≤ 0.05）。品种对日粮消化率没有影响（P≥0.81）。无论品种如何，当玉米粒被整粒喂养时，DM、OM 和淀粉的消化率都会降低（P ≤ 0.03）。品种 × 日粮（P = 0.02）对瘤胃 pH 值存在交互作用。饲喂 FGC 的安格斯公牛的瘤胃 pH 值最高，而饲喂 FGC 的荷斯坦公牛的瘤胃 pH 值与饲喂 WSC 或 DRC 的荷斯坦公牛的瘤胃 pH 值相似。品种×饮食（P = 0.28）没有相互作用，品种（P = 0.21）或饮食（P = 0.92）对总VFA浓度也没有主要影响。尽管荷斯坦公牛比安格斯公牛多吃 22% 的干物质，但它们能够维持更高 (P = 0.04) 的瘤胃 pH 值。与饲喂 WSC 相比，饲喂加工过的玉米粒后，无论加工方法如何，淀粉消化率都提高了 5%。尽管荷斯坦公牛比安格斯公牛多吃 22% 的干物质，但它们能够维持更高 (P = 0.04) 的瘤胃 pH 值。与饲喂 WSC 相比，饲喂加工过的玉米粒后，无论加工方法如何，淀粉消化率都提高了 5%。尽管荷斯坦公牛比安格斯公牛多吃 22% 的干物质，但它们能够维持更高 (P = 0.04) 的瘤胃 pH 值。与饲喂 WSC 相比，饲喂加工过的玉米粒后，无论加工方法如何，淀粉消化率都提高了 5%。