This study aimed at investigating the effects of decreasing crude protein (CP) in diets with constant rumen undegradable protein (RUP) content on dry matter (DM) intake, growth, feed efficiency (FE) and blood parameters in calves in a randomized complete block design. Dietary treatments included: (a) a calf starter containing 200 g/kg CP (62 g/kg RUP, based on DM), (b) a starter containing 180 g/kg CP (65 g/kg RUP, based on DM) and (c) a starter containing 160 g/kg CP (65 g/kg RUP, based on DM). A total 42 newborn male and female Holstein calves were fed 8 L milk/day until day 45, after which they were weaned and continued the experiment until day 75. Solid feed intake and total DM intake were measured daily, and body weight and skeletal growth parameters including withers height and heart girth were recorded weekly. Blood samples were collected on days 45 and 75. Solid feed intake, total DM intake, weaning weight, average daily gain from birth to weaning and from birth to 75 days, final weight and FE were not affected by the experimental treatments. In addition, skeletal growth parameters were similar among groups. Glucose concentration was similar among treatments; however, calves fed the starter containing 160 g/kg CP had significantly lower plasma concentrations of albumin and urea nitrogen compared with those fed starters containing 180 and 200 g/kg CP. These results indicate that CP level in the calf starter could be decreased to 160 g/kg DM if RUP levels stay at 65 g/kg DM, without negatively affecting feed intake and calf performance.

中文翻译：

---

降低含有恒定瘤胃不可降解蛋白的发酵剂饲料中粗蛋白浓度对奶牛生产性能的影响。

这项研究旨在研究在恒定完整瘤胃中恒定瘤胃不可降解蛋白质（RUP）含量的日粮中降低粗蛋白（CP）对小牛干物质（DM）摄入，生长，饲料效率（FE）和血液参数的影响设计。饮食治疗包括：（a）含200 g / kg CP（62 g / kg RUP，基于DM的小牛起子），（b）含180 g / kg CP（65 g / kg RUP，基于DM的）的小牛起子。 （c）含160 g / kg CP（65 g / kg RUP，基于DM）的发酵剂。每天给总共42只新生的雄性和雌性荷斯坦犊牛喂8升牛奶，直到第45天，然后断奶并继续进行实验直到第75天。每天测量固体饲料摄入量和DM总摄入量，以及体重和骨骼生长每周记录包括肩高和腰围在内的参数。在第45和75天收集血样。固体饲料的摄入量，总DM摄入量，断奶体重，从出生到断奶以及从出生到75天的平均日增重，最终体重和FE不受实验治疗的影响。此外，各组之间的骨骼生长参数相似。治疗之间的葡萄糖浓度相似。然而，饲喂含有160 g / kg CP的发酵剂的犊牛与饲喂含有180和200 g / kg CP的发酵剂的犊牛相比，白蛋白和尿素氮的血浆浓度明显降低。这些结果表明，如果RUP含量保持在65 g / kg DM，则小牛起子中的CP含量可降低至160 g / kg DM，而不会负面影响饲料的摄入量和小牛的生产性能。从出生到断奶以及从出生到75天的平均日增重，最终体重和FE不受实验治疗的影响。此外，各组之间的骨骼生长参数相似。治疗之间的葡萄糖浓度相似。但是，饲喂含有160 g / kg CP的发酵剂的犊牛与饲喂含有180和200 g / kg CP的发酵剂的犊牛相比，白蛋白和尿素氮的血浆浓度明显降低。这些结果表明，如果RUP含量保持在65 g / kg DM，则小牛起子中的CP含量可降低至160 g / kg DM，而不会负面影响饲料的摄入量和小牛的生产性能。从出生到断奶以及从出生到75天的平均日增重，最终体重和FE不受实验治疗的影响。此外，各组之间的骨骼生长参数相似。治疗之间的葡萄糖浓度相似。然而，饲喂含有160 g / kg CP的发酵剂的犊牛与饲喂含有180和200 g / kg CP的发酵剂的犊牛相比，白蛋白和尿素氮的血浆浓度明显降低。这些结果表明，如果RUP含量保持在65 g / kg DM，则小牛起子中的CP含量可降低至160 g / kg DM，而不会负面影响饲料的摄入量和小牛的生产性能。饲喂含160 g / kg CP的发酵剂的犊牛与饲喂含180和200 g / kg CP的发酵剂的犊牛相比，白蛋白和尿素氮的血浆浓度明显降低。这些结果表明，如果RUP含量保持在65 g / kg DM，则小牛起子中的CP含量可降低至160 g / kg DM，而不会负面影响饲料的摄入量和小牛的生产性能。饲喂含160 g / kg CP的发酵剂的犊牛与饲喂含180和200 g / kg CP的发酵剂的犊牛相比，白蛋白和尿素氮的血浆浓度明显降低。这些结果表明，如果RUP含量保持在65 g / kg DM，则小牛起子中的CP含量可降低至160 g / kg DM，而不会不利地影响采食量和小牛的生产性能。