Our objective was to measure and compare apparent ileal digestibility, standard ileal digestibility, and true ileal digestibility of crude protein (CP) and amino acids (AA) in milk replacers (MR) containing all milk proteins (WPC) or with 50% of the CP provided by an enzyme-treated soybean meal (ESBM). A T-cannula was placed in the ileum of 9 Holstein calves (8 males and 1 freemartin female) at approximately 15 d of age. After 2 wk postsurgery, calves were randomly assigned to a 3 × 3 replicated Latin square with 5-d periods. Calves were fed twice daily at a rate of 2% (dry matter) of body weight (1.25 kg/d on average), reconstituted to 15% solids, and adjusted weekly. No starter was offered to minimize rumen development. Digesta samples were collected continuously during 12 h on d 4 and 5 of each period. Basal endogenous losses of AA and CP were estimated by feeding an N-free MR to each calf during 1 period. Total endogenous losses (basal + specific; ENDtotal) were estimated by multivariate regression of the chi-squared distances between digesta and reference protein AA profiles. Ileal digesta pH with the ESBM diet was lower than that with the WPC diet. According to the piecewise nonlinear model of pH fluctuation, digesta pH during ESBM decreased more slowly after feeding and reached its nadir later than with the WPC diet. Diet did not affect average daily gain, but calves on the ESBM diet showed a bigger increment of withers height and lower mean fecal scores. The basal endogenous losses of AA and CP were 13.9 ± 1.1 and 22.4 ± 1.1 g/kg of dry matter intake, respectively. The estimated ENDtotal of AA and CP was higher with ESBM than with WPC. Accordingly, apparent ileal digestibility and standard ileal digestibility of most AA, CP, and total AA were lower or tended to be lower with ESBM. However, true ileal digestibility did not differ between diets for CP and all AA except Ala and Ile, which were greater with WPC, and Arg, which tended to be greater with ESBM. In agreement with the estimated differences in ENDtotal, we found that flows of digesta DNA and crude mucin were greater with ESBM. Substitution of 50% of the protein from whey with enzymatically treated soybean meal did not affect major nutrient digestibility or calf growth and even improved fecal consistency. Adjusting digestibilities of CP and AA in MR by endogenous protein losses is crucial when comparing bioavailability of alternative proteins and milk proteins.

中文翻译：

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仅基于乳清蛋白或酶处理豆粕的代乳品在幼小奶牛中的回肠消化率和内源性蛋白质损失。


我们的目的是测量和比较含有所有乳蛋白 (WPC) 或 50% 的代乳粉 (MR) 中粗蛋白 (CP) 和氨基酸 (AA) 的表观回肠消化率、标准回肠消化率和真实回肠消化率。 CP 由酶处理豆粕 (ESBM) 提供。在大约 15 日龄时，将 T 形插管置于 9 头荷斯坦小牛（8 头雄性和 1 头 Freemartin 雌性）的回肠中。术后 2 周后，犊牛被随机分配到 3 × 3 重复的拉丁方，周期为 5 天。犊牛每天饲喂两次，饲喂量为体重的 2%（干物质）（平均 1.25 kg/天），重新配制为 15% 固体，并每周进行调整。不提供发酵剂以最小化瘤胃发育。在每个周期的第4天和第5天的12小时内连续收集消化物样品。 AA 和 CP 的基础内源损失通过在 1 个时期内向每头犊牛饲喂不含 N 的 MR 来估计。通过消化物和参考蛋白 AA 谱之间的卡方距离的多元回归来估计总内源性损失（基础 + 特异性；ENDtotal）。 ESBM 饮食的回肠食糜 pH 值低于 WPC 饮食。根据 pH 值波动的分段非线性模型，ESBM 期间食糜 pH 值在饲喂后下降得更慢，并且比 WPC 日粮更晚达到最低点。饮食不影响平均日增重，但 ESBM 饮食的犊牛表现出较大的马肩隆高度增量和较低的平均粪便评分。 AA 和 CP 的基础内源损失分别为 13.9 ± 1.1 和 22.4 ± 1.1 g/kg 干物质摄入量。 ESBM 的 AA 和 CP 估计 ENDtotal 高于 WPC。 因此，使用 ESBM 时，大多数 AA、CP 和总 AA 的表观回肠消化率和标准回肠消化率较低或趋于较低。然而，CP 和所有 AA 饮食之间的真实回肠消化率没有差异，除了 Ala 和 Ile（WPC 中的 Ala 和 Ile 较高）和 ESBM 中的 Arg（Arg 往往较高）之外。与 ENDtotal 的估计差异一致，我们发现 ESBM 时食糜 DNA 和粗粘蛋白的流量更大。用酶处理豆粕替代 50% 的乳清蛋白不会影响主要营养素的消化率或犊牛生长，甚至改善粪便稠度。在比较替代蛋白和牛奶蛋白的生物利用度时，通过内源蛋白损失调整 MR 中 CP 和 AA 的消化率至关重要。