Department of Animal and Dairy Sciences, 1675 Observatory Drive, University of Wisconsin, Madison 53706.
Department of Animal and Dairy Sciences, 1675 Observatory Drive, University of Wisconsin, Madison 53706; Agricultural Research Service, USDA, US Dairy Forage Research Center, 1925 Linden Drive, Madison, WI 53706.
J Dairy Sci. 2021 Jun;104(6):6620-6632. doi: 10.3168/jds.2020-19835. Epub 2021 Mar 11.
This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of rumen-undegradable protein (RUP) from corn protein. Thirty-two lactating Holstein cows were blocked by days in milk and parity into 8 squares of 4 cows each in replicated 4 × 4 Latin squares. Treatments provided all supplemental crude protein from: (1) soy protein (67% expeller soybean meal plus 33% solvent soybean meal); (2) a blend of soy and corn protein (33% expeller soybean meal, 17% solvent soybean meal, 25% corn gluten meal plus 25% distillers dried grains with solubles); (3) corn protein (50% corn gluten meal plus 50% distillers dried grains with solubles); or (4) corn protein plus RPL [diet 3 top-dressed with RPL (125 g/d of AjiPro-L Generation 1, supplying an estimated 20 g of absorbable Lys/d)]. Diets contained (dry matter basis) 22% alfalfa silage, 43% corn silage, 18% ground high-moisture and dry corn, 2.4% mineral-vitamin premix, 1.5 to 3.9% soy hulls, 15% crude protein, 30 to 32% neutral detergent fiber and predicted to contain equal rumen-degradable protein, RUP, and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-wk periods before switching; production data and blood samples were collected during last 2 wk of each period. Data were analyzed using the mixed procedures of SAS. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; body weight gain was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and body weight changes were reflected by differences in milk/dry matter intake, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 (44.3 kg/d) than on diets 1, 2, and 4 (average 45.8 kg/d) and protein yield was highest on diets 1 and 2 (average 1.35 kg/d), intermediate on diet 4 (1.30 kg/d), and lowest on diet 3 (1.25 kg/d). No effects of diet were detected on ruminal metabolites. Free nonessential amino acids and total protein AA were elevated in blood plasma on diet 3, reflecting reduced utilization for milk protein synthesis. These results indicated that 50% dilution of soybean meal RUP with that from corn protein did not reduce yield and that supplementing RPL to the corn protein-based diet increased yield 1.1 kg of milk/d and 50 g of true protein/d.
本试验旨在研究瘤胃保护性赖氨酸（RPL）补充剂是否能提高玉米蛋白来源的不可降解瘤胃蛋白（RUP）的营养价值。32 头泌乳荷斯坦奶牛按产奶天数和胎次分为 8 个区组，每个区组 4 头，采用 4×4 拉丁方设计重复 4 次。处理组提供的所有补充粗蛋白来自：（1）大豆蛋白（67%膨化大豆粉加 33%溶剂浸出大豆粉）；（2）大豆和玉米蛋白混合物（33%膨化大豆粉、17%溶剂浸出大豆粉、25%玉米蛋白粉加 25%酒糟）；（3）玉米蛋白（50%玉米蛋白粉加 50%酒糟）；或（4）玉米蛋白加 RPL[日粮 3 顶部添加 RPL（AjiPro-L Generation 1，估计每天提供 20 克可吸收的赖氨酸）]。日粮（干物质基础）含 22%苜蓿青贮、43%玉米青贮、18%粉碎高水分和干玉米、2.4%矿物质-维生素预混料、1.5 至 3.9%豆壳、15%粗蛋白、30 至 32%中性洗涤纤维，预计含有等量的瘤胃可降解蛋白、RUP 和可代谢蛋白。区组内的奶牛随机分配到处理顺序，并在更换前进行为期 4 周的饮食喂养；在每个周期的最后 2 周收集生产数据和血液样本。数据采用 SAS 的混合程序进行分析。日粮 1 的采食量最高，日粮 2 和 3 的采食量居中，日粮 4 的采食量最低；日粮 3 的体重增加量最高，日粮 1 和 2 的体重增加量居中，日粮 4 的体重增加量最低。采食量和体重变化反映在牛奶/干物质采食量的差异上，日粮 2 和 4 的牛奶/干物质采食量最高，日粮 3 的牛奶/干物质采食量最低。日粮 3 的产奶量（44.3 千克/天）低于日粮 1、2 和 4（平均 45.8 千克/天），日粮 3 的蛋白质产量最高（1.35 千克/天），日粮 4 居中（1.30 千克/天），日粮 3 最低（1.25 千克/天）。日粮对瘤胃代谢物没有影响。日粮 3 血浆中游离非必需氨基酸和总蛋白 AA 升高，反映出用于合成乳蛋白的利用率降低。这些结果表明，用玉米蛋白稀释 50%的大豆粉 RUP 不会降低产奶量，而向基于玉米蛋白的日粮中添加 RPL 可使产奶量增加 1.1 千克/天和真蛋白 50 克/天。
