Forty 12-day-old lambs with an average BW of 6.37 kg were allocated in a completely randomized design with a 2 × 2 factorial arrangement to evaluate the effects of wheat straw feeding level (WS; 10% vs. 25%, DM basis) and rumen undegradable to degradable protein ratio [RUP:RDP; low ratio (LR) = 27:73; high ratio (HR) = 38:62] on growth performance, nutrient digestibility, ruminal fermentation, microbial protein yield (MPY), blood metabolites, and liver enzymes. Treatments (10 lambs/each; 5 males and 5 females) were: (1) 10% WS with low RUP:RDP ratio (10WS-LR); (2) 10% WS with high RUP:RDP ratio (10WS-HR); (3) 25% WS with low RUP:RDP ratio (25WS-LR); and (4) 25% WS with high RUP:RDP ratio (25WS-HR). Lambs were weaned on d 82 of the experiment and remained in the study until d 92. Lambs had free access to starter diet throughout the experiment. Results show that starter intake, average daily gain, and feed efficiency did not change among experimental treatments. Organic matter digestibility was reduced in 25WS diets. Greater organic matter digestibility, fibre digestibility (tendency; p = 0.064), wither height (d 82), and urinary allantoin was found in HR compared to LR diets. However, ruminal NH₃-N concentration and urinary nitrogen excretion was greater in LR diets indicating lower nitrogen utilization efficiency. The greatest ruminal butyrate concentration as well as the greatest concentration of blood beta-hydroxybutyrate was found for 25WS-HR diet at d 90 of experiment. The blood urea concentration was reduced in HR diets compared to LR diets. In summary, high RUP:RDP ratio is advisable when young lambs received high level of WS in starter diet due to improve nutrient digestibility and nitrogen efficiency.

以2×2因子排列的完全随机设计分配40只平均体重为6.37 kg的羔羊，以评估小麦秸秆饲喂水平的影响（WS； 10％vs. 25％，以DM为基础）瘤胃中不可降解蛋白质与可降解蛋白质的比例[RUP：RDP; 低比率（LR）= 27:73；高比率（HR）= 38:62]对生长性能，营养物质消化率，瘤胃发酵，微生物蛋白产量（MPY），血液代谢产物和肝酶的影响。治疗方法（每只羊羔10只；雄性5只，雌性5只）：（1）10％WS，RUP：RDP比低（10WS-LR）；（2）10％WS具有高RUP：RDP比（10WS-HR）；（3）25％WS，RUP：RDP比低（25WS-LR）；（4）25％的WS具有高的RUP：RDP比（25WS-HR）。在实验的第82天断奶，并在研究中一直待到第92天。在整个实验过程中，羔羊可以自由进食初学者饮食。结果表明，在实验处理之间，初学者的摄入量，平均日增重和饲料效率没有变化。25WS日粮中有机物的消化率降低。更高的有机物消化率，纤维消化率（趋向；与LR日粮相比，在HR中发现了p = 0.064），身高（d 82）和尿尿囊素。但是，LR日粮中瘤胃中的NH ₃ -N浓度和尿中氮的排泄量较大，表明氮的利用效率较低。在实验的90天时，发现25WS-HR饮食的最大瘤胃丁酸酯浓度以及最大血β-羟基丁酸酯浓度。与LR日粮相比，HR日粮中的血尿素浓度降低了。总之，当初生羔羊在日粮中摄入较高水平的WS时，建议提高RUP：RDP的比例，这是因为提高了养分的消化率和氮效率。