Abstract Thirty-two Holstein heifers with mean (± standard error of the mean) age of 6.5 months (±0.12) and live weight (LW) of 166 kg (±1.6) were divided into four groups of eight animals to evaluate the effect of forage source and the concentrations of rumen-undegradable crude protein (RUP) in the diet with a 2 × 2 factorial design. As forage sources cowpea hay (Vigna sinensis L.) or pangola grass hay (Digitaria decumbens Stend) were added to the diet at 250 g/kg dry matter (DM). Also, 350 g/kg DM of chopped fresh King grass (Pennisetum purpureum Schum.) was included in all diets. The RUP proportions were 260 or 360 g/kg of total crude protein (CP). Heifers were housed in metabolism cages. The trial lasted ten weeks, with the first two weeks used for adaptation and the last week for data collection and sampling. Diets had a forage to concentrate ratio of 60:40 (on DM basis), and were offered as total mixed rations ad libitum. Fish meal or urea were used to produce varying concentrations of RUP at similar dietary CP content. Diet ingredients (i.e., hay, grass, and concentrate) and feces were sampled for nutrient analysis. Total collection of feces was performed to estimate apparent total tract nutrient digestibility (ATTD). Urinary purine derivative excretions were determined from urine spot samples to estimate rumen microbial protein synthesis. The effects of forage source, RUP, and its interactions were determined by general linear model analysis. Replacing dietary pangola grass hay with cowpea hay increased daily intakes of DM, organic matter, CP, acid detergent fiber (ADF), and digestible organic matter, and ATTD of DM, organic matter, neutral detergent fiber, and ADF (P

中文翻译：

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饲草来源和日粮瘤胃不可降解蛋白对奶牛营养利用和生长的影响

摘要 将平均年龄（± 平均标准误差）为 6.5 个月（±0.12）、活重（LW）为 166 kg（±1.6）的 32 头荷斯坦小母牛分成四组，每组 8 只，以评估饲料来源和日粮中瘤胃不可降解粗蛋白 (RUP) 的浓度，采用 2 × 2 析因设计。作为饲料来源豇豆干草 (Vigna sinensis L.) 或潘哥拉草干草 (Digitaria decumbens Stend) 以 250 g/kg 干物质 (DM) 添加到饮食中。此外，所有饮食中都包含 350 g/kg DM 切碎的新鲜王草（Pennisetum purpureum Schum.）。RUP 比例为 260 或 360 g/kg 的总粗蛋白 (CP)。小母牛饲养在代谢笼中。试验持续了十周，前两周用于适应，最后一周用于数据收集和采样。日粮的草料与浓缩物的比例为 60:40（以干物质为基础），并作为随意的总混合日粮提供。使用鱼粉或尿素生产不同浓度的 RUP，日粮 CP 含量相似。对饮食成分（即干草、草和浓缩物）和粪便取样进行营养分析。进行粪便的总收集以估计表观总消化道养分消化率（ATTD）。从尿斑样品中测定尿嘌呤衍生物的排泄量，以估计瘤胃微生物蛋白质的合成。草料来源、RUP 及其相互作用的影响由一般线性模型分析确定。用豇豆干草代替膳食潘戈拉草干草增加了 DM、有机物、CP、酸性洗涤纤维 (ADF) 和可消化有机物的每日摄入量，以及 DM、有机物的 ATTD，