The objectives were to compare the effectiveness of poultry by-product meal (PBM) with xylose-treated soybean meal (x-SBM) as a conventional protein source and rumen-undegraded protein (RUP):rumen-degraded protein (RDP) ratio on nutrient digestibility, nitrogen metabolism, and production of early- to mid-lactation Holsteins. Twelve multiparous cows averaging (mean ± SD) 50 ± 9 days in milk were randomly assigned to a replicated 4 × 4 Latin square design within a 2 × 2 factorial arrangement of treatments. Each period was 28 days in length. Treatments were RUP sources (PBM or x-SBM) with either a high or a low RUP:RDP ratio (high ratio = 40:60 or low ratio = 36:64; based on % of crude protein (CP)). Experimental diets were balanced to be similar in protein and energy contents (CP = 16.7% of DM; NE_L = 1.67 Mcal/kg DM). Prior to diet formulation, an in situ pilot experiment was conducted to estimate the RUP fractions of x-SBM and PBM as 63.9% and 54.1% of CP, respectively. Treatments had no effect on ruminal pH and total volatile fatty acid (VFA) and molar percentage of individual VFAs. Treatments had no effect on total tract apparent digestibility of DM, OM, and neutral detergent fiber (NDF), with the exception of N that was greater in diets with a low RUP:RDP ratio (68.2 vs. 70.1% of DM). DM consumption was 0.70 kg/day higher when cows were fed PBM diet compared with x-SBM diet. No treatment effect was observed on milk yield and milk composition; however, milk protein yield and milk urea N were greater in cows fed PBM. Inclusion of PBM in the diet in substitution to x-SBM resulted in increased blood levels of urea N, cholesterol, and non-esterified fatty acid (NEFA). There was no interaction between the RUP source and the RUP:RDP ratio for urinary and fecal N excretion. Efficiency of N utilization expressed as milk N secretion as a proportion of N intake tended to be greater in cows fed PBM. Feeding diets with a low ratio of RUP:RDP increased efficiency of milk production expressed as milk yield as a proportion of total N excretion (fecal and urinary N). Feeding a diet with PBM supported milk production comparable with x-SBM and had positive effects on feed intake, milk protein yield, and milk N efficiency.

目的是比较家禽副产品粉（PBM）与木糖处理的大豆粉（x-SBM）作为常规蛋白质来源的效率，以及瘤胃未降解蛋白质（RUP）：瘤胃降解蛋白质（RDP）的比例。营养物质的消化率，氮代谢和哺乳早期至中期的荷斯坦牛。在2×2处理安排中，将十二头平均产奶量为50±9天（平均±标准差）的多头母牛随机分配到重复的4×4拉丁方形设计中。每个时期为28天。处理是具有高或低RUP：RDP比率（高比率= 40:60或低比率= 36:64；基于粗蛋白（CP）的百分比）的RUP来源（PBM或x-SBM）。实验饮食的蛋白质和能量含量保持平衡（CP = DM的16.7％； NE _L = 1.67 Mcal / kg DM）。在饮食配方之前，进行了原位先导实验以估计x-SBM和PBM的RUP分数分别为CP的63.9％和54.1％。处理对瘤胃pH，总挥发性脂肪酸（VFA）和单个VFA的摩尔百分比没有影响。处理对DM，OM和中性清洁剂纤维（NDF）的总表观消化率没有影响，但RUP：RDP比率低的日粮中氮含量较高（68.2比DM的70.1％）。与x-SBM饲喂相比，饲喂PBM饲喂奶牛的DM消耗量每天高0.70千克。没有观察到对奶产量和奶成分的治疗效果；然而，饲喂PBM的奶牛的牛奶蛋白产量和牛奶尿素氮更高。饮食中将PBM替代x-SBM会导致血液中尿素氮，胆固醇，和非酯化脂肪酸（NEFA）。RUP源与尿和粪便N排泄的RUP：RDP比之间没有相互作用。饲喂PBM的奶牛的氮利用效率表示为牛奶中氮的分泌，占氮摄入的比例较高。用低比例的RUP：RDP饲喂日粮可以提高产奶效率，以产奶量占总N排泄（粪便和尿N）的比例表示。用PBM饲喂日粮可提供与x-SBM相当的牛奶产量，并且对采食量，牛奶蛋白质产量和牛奶氮效率具有积极影响。用低比例的RUP：RDP饲喂日粮可以提高产奶效率，以产奶量占总N排泄（粪便和尿N）的比例表示。用PBM饲喂日粮可提供与x-SBM相当的牛奶产量，并且对采食量，牛奶蛋白质产量和牛奶氮效率具有积极影响。用低比例的RUP：RDP饲喂日粮可以提高产奶效率，以产奶量占总N排泄（粪便和尿N）的比例表示。用PBM饲喂日粮可提供与x-SBM相当的牛奶产量，并且对采食量，牛奶蛋白质产量和牛奶氮效率具有积极影响。