Soybeans can provide ruminally degradable protein, lipid and metabolizable amino acid (AA) to lactating dairy cows; however, soy-based trypsin inhibitors can limit protein digestion in nonruminants. Eight ruminally cannulated lactating Holstein cows were used to evaluate the impacts of soy-based trypsin inhibitors on nutrient disappearance, lactation, and plasma AA bioavailability. Treatments were abomasal infusion of 0 or 400 g/d casein or a crystalline AA analog of casein with unroasted or roasted soybeans fed at 10% dry matter. Data were analyzed using the MIXED procedure of SAS. Measures of digestion were determined from fecal output determined with acid detergent insoluble ash and urine output determined from measures of urine creatinine. Neither soybean processing (P ≥ 0.20) or source of abomasal infusion (P ≥ 0.60) impacted nutrient digestibility. Ruminal ammonia, isobutyrate, and isovalerate were increased (P ≤ 0.01) among cattle consuming unroasted soybeans. Source of infusion did not affect (P ≥ 0.38) ruminal volatile fatty acids or nitrogen metabolism. Ruminal N metabolism was largely unaffected by soybean processing although microbial N efficiency was greater (P < 0.01) among cows fed unroasted soybeans. Dry matter intake and energy-corrected milk were greater (P < 0.01) in cows fed roasted compared to unroasted soybeans. The proportion of fat, protein, lactose and solids not fat in milk did not differ between soybean processing or postruminal AA source, but fat, protein, lactose and solids not fat yield was greater (P ≤ 0.01) when cows were fed roasted soybeans because milk yields were greater when cows were fed roasted vs unroasted soybeans. As expected, infusion of casein or its crystalline AA analog increased plasma essential AA and milk urea nitrogen concentration. The rate of increase in essential AA concentration in plasma was 2.9-times greater for casein than for crystalline AA. These data seem to indicate that soy-based trypsin inhibitors have no impacts on postruminal AA bioavailability when fed to cows and that MP from casein is greater than from crystalline AA.

中文翻译：

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加热大豆对泌乳牛瘤胃后氨基酸生物利用度、生产性能和瘤胃发酵的影响

大豆可为泌乳奶牛提供瘤胃可降解蛋白质、脂质和可代谢氨基酸（AA）；然而，大豆胰蛋白酶抑制剂会限制非反刍动物的蛋白质消化。使用八头瘤胃插管的泌乳荷斯坦奶牛来评估大豆胰蛋白酶抑制剂对营养消失、泌乳和血浆 AA 生物利用度的影响。处理方法是向皱胃输注 0 或 400 g/d 酪蛋白或酪蛋白的结晶 AA 类似物，并以 10% 干物质饲喂未烤或烤的大豆。使用 SAS 的 MIXED 程序分析数据。消化的测量是根据用酸性洗涤剂不溶性灰分确定的粪便排出量确定的，并且根据尿肌酸酐的测量确定的尿排出量确定的。大豆加工 (P ≥ 0.20) 或皱胃浸液来源 (P ≥ 0.60) 均不会影响营养物质消化率。食用未烤大豆的牛的瘤胃氨、异丁酸和异戊酸增加（P≤0.01）。输注来源不影响（P≥0.38）瘤胃挥发性脂肪酸或氮代谢。尽管饲喂未烤大豆的奶牛的微生物氮效率更高（P＜0.01），但瘤胃氮代谢在很大程度上不受大豆加工的影响。与未烤大豆相比，烤大豆的奶牛干物质摄入量和能量校正奶量更高（P < 0.01）。牛奶中脂肪、蛋白质、乳糖和非脂肪固体的比例在大豆加工或瘤胃后 AA 来源之间没有差异，但当奶牛饲喂烤大豆时，脂肪、蛋白质、乳糖和非脂肪固体产量更高 (P ≤ 0.01)，因为饲喂烤大豆的奶牛比饲喂未烤大豆的奶牛产奶量更高。正如预期的那样，输注酪蛋白或其结晶 AA 类似物增加了血浆必需 AA 和乳尿素氮浓度。酪蛋白血浆中必需 AA 浓度的增加率是结晶 AA 的 2.9 倍。这些数据似乎表明，当饲喂奶牛时，基于大豆的胰蛋白酶抑制剂对瘤胃后 AA 生物利用度没有影响，并且来自酪蛋白的 MP 高于来自结晶 AA 的 MP。