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 (NEL) 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 NEL (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 NEL 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.

中文翻译：

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等能高淀粉或高脂肪日粮对泽西奶牛能量和氮分配和利用的影响。

本研究的目的是确定等能高淀粉或高脂肪饮食对能量和 N 分配和能量利用的影响。十二头经产的泽西奶牛（平均±标准差；牛奶 192±11 天；467±47 公斤）采用交叉设计，28 天周期（24 天适应和 4 天收集）用于比较 2 种处理日粮。处理为高淀粉（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）。根据国家研究委员会 (2001) 乳制品模型，日粮配制成具有 1.55 Mcal/kg 干物质的净泌乳能量 (NEL) 含量。主要通过用瘤胃惰性脂肪源和 HF 中的棉籽壳代替 HS 中的玉米粒来改变营养成分。HS 的总能量含量较低（4.43 对 4.54 ± 0.01 Mcal/kg 干物质），而可消化（2.93 对 2.74 ± 0.035 Mcal/kg 干物质）和代谢能（2.60 对 2.41 ± 0.030 Mcal/kg 干物质） kg 干物质）和 NEL（1.83 与 1.67 ± 0.036 Mcal/kg 干物质）含量都高于 HF。HS 以体脂肪形式沉积的组织能量往往更高（4.70 vs. 2.14 ± 1.01 Mcal/d）。对于 N 分配，HS 增加牛奶 N 分泌（141 对 131 ± 10.5 g/d）并减少尿 N 排泄（123 对 150 ± 6.4 g/d）。与HF相比，HS提高了干物质（66.7 vs. 61.7 ± 1.06%）、有机物质（68.5 vs. 63.2 ± 0.98%）、能量（66.0 vs. 60.4 ± 0.92%）、和 18 碳脂肪酸（67.9 对 61.2 ± 1.60%）。然而，HS 的淀粉表观总消化率从 97.0 降低到 94.5 ± 0.48%。与HF相比，HS倾向于增加牛奶产量（19.7 vs. 18.9 ± 1.38 kg/d）、乳蛋白含量（4.03 vs. 3.93 ± 0.10%）、乳蛋白产量（0.791 vs. 0.740 ± 0.050 kg/d）、和牛奶乳糖产量（0.897 vs. 0.864 ± 0.067 kg/d）。此外，HS 降低了乳脂含量（5.93 vs. 6.37 ± 0.15%），但不影响乳脂产量（平均 1.19 ± 0.09 kg/d）或能量校正产奶量（平均 27.2 ± 1.99 kg/d） . 当前研究的结果表明，HS 饮食具有更高的代谢能和 NEL 含量，增加了 N 向乳汁分泌和远离尿液排泄的分配，并且可能增加了向以脂肪形式沉积的组织能量分配的能量。