Abstract The hypothesis of the current study was that steam-flaking corn grain will increase ruminal available starch, but reduce undegradable protein reaching the small intestine and hence formulating the starter diet with higher undegradable protein content may influence dairy calf performance. The effects of corn processing method (ground corn grain; GC vs. steam-flaked corn grain; SFC) with rumen undegradable to degradable protein ratios [low ratio (LR) = 28:72; high ratio (HR) = 37:63 based on %CP] on growth performance, feeding behavior, nutrients digestibility, ruminal fermentation, urinary purine derivatives and blood metabolites of Holstein dairy calves were evaluated. Forty-eight 3-day-old calves (24 females and 24 males) with a starting BW of 39.5 kg were used in a completely randomized block design with a 2 × 2 factorial arrangement of treatments. Experimental treatments were: (1) ground corn with low RUP:RDP (GC-LR); (2) ground grain with high RUP:RDP (GC-HR); (3) steam-flaked corn with low RUP:RDP (SFC-LR); and (4) steam-flaked corn with high RUP:RDP (SFC-HR). All calves were weaned on d 63 of age and, remained in the study until d 83 to take final measurements. Starter intake was not influenced by the grain processing method nor by dietary RUP:RDP ratio; however, the average daily gain and feed efficiency were improved and final body weight was higher in SFC fed calves. Feeding SFC diet improved the faecal score, increased the time spent on eating and slightly increased ruminating time. The LR diet improved neutral detergent fiber digestibility. Greater ruminal concentrations for total short-chain fatty acids, propionate, and butyrate were obtained when calves fed on SFC diet in pre-weaning period. The greatest heights for both wither and hip among experimental treatments were obtained in SFC-HR treatment. The higher urinary allantoin excretion and microbial protein yield, and lower urinary nitrogen excretion on the other hand, reflected an improved nitrogen efficiency in the SFC diet compared to the GC diet. Blood concentrations for glucose, beta-hydroxybutyrate and insulin were higher, and blood urea nitrogen concentration was lower in calves fed on SFC diet. In conclusion, considering our experimental condition, feeding steam-flaked corn in starter diet of dairy calves is favourable compared to ground corn grain, but RUP:RDP ratio did not influence animal performance per se. Skeletal growth was improved when SFC was fed with greater RUP:RDP ratio in starter diet which may be recommendable in replacement heifer rearing programs.

中文翻译：

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瘤胃不可降解蛋白与可降解蛋白比例的玉米谷物加工方法（磨碎与蒸汽压片）对荷斯坦奶牛生长性能、瘤胃发酵和微生物蛋白产量的影响

摘要 本研究的假设是，蒸汽压片玉米粒会增加瘤胃可用淀粉，但会减少到达小肠的不可降解蛋白质，因此配制具有较高不可降解蛋白质含量的起始日粮可能会影响奶牛的生产性能。玉米加工方法（磨碎的玉米粒；GC 与蒸汽压片玉米粒；SFC）对瘤胃不可降解蛋白与可降解蛋白比率的影响 [低比率 (LR) = 28:72; 高比率 (HR) = 37:63 基于 %CP] 对荷斯坦奶牛的生长性能、饲养行为、营养物质消化率、瘤胃发酵、尿嘌呤衍生物和血液代谢物进行了评估。48 头 3 日龄小牛（24 头雌性和 24 头雄性），起始体重为 39。5 kg 用于具有 2 × 2 因子排列处理的完全随机区组设计。实验处理是：(1)低RUP:RDP(GC-LR)的磨碎的玉米；(2) 高 RUP:RDP (GC-HR) 的磨粒；(3) 低 RUP:RDP (SFC-LR) 的蒸汽压片玉米；(4) 具有高 RUP:RDP (SFC-HR) 的蒸汽压片玉米。所有小牛在第 63 天断奶，并留在研究中直到第 83 天进行最终测量。开胃菜的摄入量不受谷物加工方法和膳食 RUP:RDP 比例的影响；然而，SFC 喂养的犊牛的平均日增重和饲料效率得到提高，最终体重更高。饲喂 SFC 饮食改善了粪便评分，增加了进食时间并略微增加了反刍时间。LR 饮食提高了中性洗涤纤维的消化率。当犊牛在断奶前以 SFC 日粮喂养时，瘤胃中总短链脂肪酸、丙酸和丁酸的浓度更高。在 SFC-HR 治疗中获得了实验治疗中马肩隆和臀部的最大高度。较高的尿尿囊素排泄量和微生物蛋白产量，以及较低的尿氮排泄量，反映了与 GC 饮食相比，SFC 饮食中氮效率的提高。以 SFC 饮食喂养的小牛的葡萄糖、β-羟基丁酸和胰岛素的血液浓度较高，而血尿素氮浓度较低。总之，考虑到我们的实验条件，与磨碎的玉米粒相比，在奶牛的开食料中饲喂蒸汽压片玉米是有利的，但 RUP:RDP 比率本身并不影响动物性能。