Abstract：
This study was conducted to determine if the decreased MP supply predicted by the NRC (2001) when canola meal (CM) substitutes soybean meal (SBM) was supported by direct measurement of net portal absorption of AA or energy-yielding nutrients, plus the impact of the type of forage in CM-based rations. Nine Holstein cows with indwelling catheters in splanchnic blood vessels, 8 also with a ruminal cannula were used to examine the effects of protein source in corn silage-based diets, comparing SBM versus CM, and forage source in CM-based diets, comparing corn versus grass silage. The cows were allocated to a triple 3 × 3 Latin square design with 21-d periods. The 3 experimental diets, formulated to be isoenergetic and isonitrogenous, were based on: 1) SBM and corn silage (SoyCorn); 2) CM and corn silage (CanCorn) and 3) CM and cool-season grass silage (CanGrass). Averages of intake, milk yield and milk composition of the last 3 d of each period were used for statistical analyses. On d 21 of each period, 6 sets of arterial, portal, hepatic and mammary blood samples and 2 ruminal fluid samples were collected. On d 12 of period 2, the protein sources were incubated in nylon bags to determine 16h-ruminal disappearance of DM and N and to obtain 16-h residues. Finally, 5 d after the completion of the Latin square design, the mobile bag technique was used to determine DM and N intestinal disappearance of the 16-h residues of SBM and CM. Pre-planned contrasts were used to compare the effect of the protein source in cows fed corn silage, i.e., SoyCorn versus CanCorn, and the effect of forage in cows fed CM, i.e., CanCorn versus CanGrass. Data of the cow without a rumen canula could not be used because of health problem. In corn silage-based diets, substitution of SBM by CM tended to increase milk (6%) and milk fat (7%) yields. The 8% higher ruminal N disappearance and the 19% decreased MP supply from RUP predicted by NRC (2001) were not supported by the 25% decrease in ruminal ammonia concentration, similar net portal absorption of AA (except 22% higher for Met), and the 14% decrease in urea hepatic removal when CM substituted SBM. Ruminal incubation of CM in nylon bags does not appear suitable for adequate determination of the rumen by-pass of a protein source like CM. Inclusion of grass silage rather than corn silage in CM-based diets tended to increase milk (6%) and increased milk lactose (8%) yields. Neither protein nor forage source resulted in variations of metabolism of energy-yielding nutrients that could explain observed increments in cow performance. The present study indicates no decreased AA availability when CM substitutes SBM. Therefore, substitution of SBM by CM in diets based on corn silage and CM in corn- or grass silage-diets can be used successfully in high producing dairy cows.
摘要：
进行这项研究是为了确定NRC（2001）预测的当油菜粉（CM）替代品豆粕（SBM）时MP供应减少是否通过直接测量AA或能量产生营养素的净门户吸收来支持，以及基于CM的口粮中牧草类型的影响。九头荷斯坦奶牛在内脏血管中留置导管，8也用瘤胃套管检查蛋白质来源在玉米青贮饲料为基础的饮食的影响，比较SBM与CM，以CM为基础的饮食中的饲料来源，比较玉米和草青贮。将母牛分配给3×3拉丁正方形设计，周期为21天。3种实验性饮食，配制为等能和等氮，基于：1）SBM和玉米青贮（SoyCorn）；2）CM和玉米青贮（CanCorn）和3）CM和冷季草青贮（CanGrass）。平均摄入量，对每个周期最后3d的产奶量和乳成分进行统计分析。在每个周期的d21，6组动脉，门户，收集肝和乳腺血样和2个瘤胃液样本。在第2期的第12天，将蛋白质源在尼龙袋中孵育，以确定DM和N的16h瘤胃消失，并获得16h残基。最后,5d拉丁广场设计完成后，移动袋技术用于确定SBM和CM的16小时残留的DM和N肠消失。使用预先计划的对比来比较蛋白质来源在饲喂玉米青贮的奶牛中的效果，即，大豆玉米对CanCorn,以及饲喂CM的奶牛的饲料效果，即，CanCorn与CanGrass。由于健康问题，无法使用没有瘤胃插管的母牛的数据。在以玉米青贮饲料为基础的饮食中，用CM代替SBM倾向于增加牛奶（6％）和牛奶脂肪（7％）的产量。由NRC(2001)预测的来自RUP的8%较高的瘤胃N消失和19%的减少的MP供应没有被瘤胃氨浓度25%的减少所支持,类似的AA净门户吸收(除了大都会会议高出22%)，CM替代SBM时，尿素肝去除量降低了14%。CM在尼龙袋中的瘤胃孵育似乎不适合充分确定蛋白质来源如CM的瘤胃旁路。在基于CM的饮食中加入草青贮饲料而不是玉米青贮饲料倾向于增加牛奶（6％）和牛奶乳糖（8％）的产量。蛋白质和牧草来源均未导致产生能量的营养素代谢的变化，这可以解释观察到的奶牛性能增加。本研究表明，当CM替代SBM时，AA的可用性没有降低。因此,在基于玉米青贮的日粮中，用CM代替SBM，在玉米或草青贮日粮中，CM可以成功地用于高产奶牛。
