Department of Animal Science, University of Nebraska, Lincoln 68583.
Department of Biological Systems Engineering, University of Nebraska, Lincoln 68583.
J Dairy Sci. 2020 May;103(5):4378-4389. doi: 10.3168/jds.2019-17638. Epub 2020 Mar 18.
The objective of this study was to determine the effects of high-starch or high-fat diets formulated to be isoenergetic on energy and N partitioning and utilization of energy. Twelve multiparous Jersey cows (mean ± standard deviation; 192 ± 11 d in milk; 467 ± 47 kg) in a crossover design with 28-d periods (24-d adaptation and 4-d collection) were used to compare 2 treatment diets. Treatments were high starch (HS; 30.8% starch, 31.8% neutral detergent fiber, and 1.9% fatty acids) or high fat (HF; 16.8% starch, 41.7% neutral detergent fiber, and 4.1% fatty acids). Diets were formulated to have net energy for lactation (NE) content of 1.55 Mcal/kg of dry matter according to the National Research Council (2001) dairy model. Nutrient composition was varied primarily by replacing corn grain in HS with a rumen-inert fat source and cottonseed hulls in HF. Gross energy content was lower for HS (4.43 vs. 4.54 ± 0.01 Mcal/kg of dry matter), whereas digestible (2.93 vs. 2.74 ± 0.035 Mcal/kg of dry matter) and metabolizable energy (2.60 vs. 2.41 ± 0.030 Mcal/kg of dry matter), and NE (1.83 vs. 1.67 ± 0.036 Mcal/kg of dry matter) content were all greater than for HF. Tissue energy deposited as body fat tended to be greater for HS (4.70 vs. 2.14 ± 1.01 Mcal/d). For N partitioning, HS increased milk N secretion (141 vs. 131 ± 10.5 g/d) and decreased urinary N excretion (123 vs. 150 ± 6.4 g/d). Compared with HF, HS increased apparent total-tract digestibility of dry matter (66.7 vs. 61.7 ± 1.06%), organic matter (68.5 vs. 63.2 ± 0.98%), energy (66.0 vs. 60.4 ± 0.92%), and 18-carbon fatty acids (67.9 vs. 61.2 ± 1.60%). However, apparent total-tract digestibility of starch decreased for HS from 97.0 to 94.5 ± 0.48%. Compared with HF, HS tended to increase milk yield (19.7 vs. 18.9 ± 1.38 kg/d), milk protein content (4.03 vs. 3.93 ± 0.10%), milk protein yield (0.791 vs. 0.740 ± 0.050 kg/d), and milk lactose yield (0.897 vs. 0.864 ± 0.067 kg/d). In addition, HS decreased milk fat content (5.93 vs. 6.37 ± 0.15%) but did not affect milk fat yield (average of 1.19 ± 0.09 kg/d) or energy-corrected milk yield (average of 27.2 ± 1.99 kg/d). Results of the current study suggest that the HS diet had a greater metabolizable energy and NE content, increased partitioning of N toward milk secretion and away from urinary excretion, and may have increased partitioning of energy toward tissue energy deposited as fat.
本研究旨在确定以等能量方式配制的高淀粉或高脂肪日粮对能量和 N 分配以及能量利用的影响。12 头经产荷斯坦奶牛（平均 ± 标准差；泌乳 192 ± 11 d；467 ± 47 kg）采用交叉设计，每个周期 28 d（24 d 适应和 4 d 收集），比较了 2 种处理日粮。处理组为高淀粉（HS；30.8%淀粉、31.8%中性洗涤纤维和 1.9%脂肪酸）或高脂肪（HF；16.8%淀粉、41.7%中性洗涤纤维和 4.1%脂肪酸）。日粮的泌乳净能（NE）含量根据国家研究委员会（2001 年）奶牛模型设计为 1.55 Mcal/kg 干物质。营养成分的主要变化是通过用瘤胃惰性脂肪源和棉籽壳代替 HS 中的玉米谷物来实现的。HS 的总能含量较低（4.43 与 4.54 ± 0.01 Mcal/kg 干物质），而可消化（2.93 与 2.74 ± 0.035 Mcal/kg 干物质）和可代谢能量（2.60 与 2.41 ± 0.030 Mcal/kg 干物质）以及 NE（1.83 与 1.67 ± 0.036 Mcal/kg 干物质）含量均高于 HF。作为体脂储存的组织能量倾向于 HS 较高（4.70 与 2.14 ± 1.01 Mcal/d）。对于 N 分配，HS 增加了牛奶 N 分泌（141 与 131 ± 10.5 g/d）和减少了尿 N 排泄（123 与 150 ± 6.4 g/d）。与 HF 相比，HS 增加了干物质（66.7 与 61.7 ± 1.06%）、有机物（68.5 与 63.2 ± 0.98%）、能量（66.0 与 60.4 ± 0.92%）和 18 碳脂肪酸（67.9 与 61.2 ± 1.60%）的表观全肠道消化率。然而，HS 的淀粉表观全肠道消化率从 97.0 下降到 94.5 ± 0.48%。与 HF 相比，HS 倾向于增加产奶量（19.7 与 18.9 ± 1.38 kg/d）、牛奶蛋白含量（4.03 与 3.93 ± 0.10%）、牛奶蛋白产量（0.791 与 0.740 ± 0.050 kg/d）和牛奶乳糖产量（0.897 与 0.864 ± 0.067 kg/d）。此外，HS 降低了牛奶脂肪含量（5.93 与 6.37 ± 0.15%），但不影响牛奶脂肪产量（平均 1.19 ± 0.09 kg/d）或校正奶能量产量（平均 27.2 ± 1.99 kg/d）。本研究结果表明，HS 日粮具有更高的可代谢能量和 NE 含量，增加了 N 向牛奶分泌的分配，减少了尿排泄，并且可能增加了能量向体脂沉积的分配。
