Department of Dairy Science, Virginia Tech, Blacksburg 24061.
College of Animal Science and Technology, Zhejiang A&F University, Hangzhou 311300, China.
J Dairy Sci. 2019 Dec;102(12):10983-10996. doi: 10.3168/jds.2019-16597. Epub 2019 Sep 20.
Nitrogen efficiency in dairy cows can be improved by more precisely supplying essential amino acids (EAA) relative to animal needs, which requires accurate estimates of the availability of individual EAA from feedstuffs. The objective of this study was to determine EAA availability for 7 feed ingredients. Seven heifers (258 ± 28 kg BW) were randomly chosen and assigned to 8 treatment sequences in a 7 × 8 incomplete Latin square design. Treatments were a basal diet (BD), and 10% (on a dry matter basis) of BD replaced by corn silage (CS), grass hay (GH), alfalfa hay (AH), dried distillers grain (DDGS), soybean hulls (SH), wet brewers grain (BG), or corn grain (CG). Total plasma AA entry rates were estimated for each EAA within each diet by fitting a 4-pool dynamic model to observed plasma, C AA enrichment resulting from a 2-h constant infusion of a C algal AA mixture. Individual EAA availability from each test ingredient was determined by regression of entry rates for that AA on crude protein intake for each ingredient. The derived plasma total EAA entry rates for corn silage, grass hay, alfalfa hay, dried distillers grain, soyhulls, brewers grain, and corn grain were 30.6 ± 3.4, 27.4 ± 3.2, 31.3 ± 3.4, 37.2 ± 3.2, 26.4 ± 3.2, 37.8 ± 3.2, and 33.5 ± 3.2% (±standard error) of EAA from each ingredient, respectively. Using the previous estimate of 8.27% EAA utilization by splanchnic tissues during first pass, total rumen-undegradable protein EAA absorbed from the gut lumen was 33.4, 29.9, 34.1, 40.6, 28.8, 41.2, and 36.5% of the EAA in each ingredient respectively.
奶牛的氮效率可以通过更精确地供应必需氨基酸（EAA）来提高，这需要准确估计饲料中单个 EAA 的可利用性。本研究的目的是确定 7 种饲料成分的 EAA 可利用性。选择 7 头荷斯坦奶牛（258±28kgBW），采用 7×8 不完全拉丁方设计随机分为 8 个处理组。处理组包括基础日粮（BD）和 10%（干物质基础）的 BD 分别用玉米青贮（CS）、干草（GH）、苜蓿干草（AH）、DDGS、大豆皮（SH）、湿酒糟（BG）或玉米谷物（CG）替代。通过拟合 4 池动态模型来估计每个日粮中每个 EAA 的血浆 AA 总进入率，该模型是根据 2 小时恒定输注 C 藻类 AA 混合物后观察到的血浆和 C AA 富集来拟合的。通过回归每个测试成分的该 AA 的进入率与该成分的粗蛋白摄入量来确定每个成分的 EAA 可利用性。玉米青贮、干草、苜蓿干草、DDGS、大豆皮、酒糟、玉米谷物的血浆总 EAA 进入率分别为各自饲料中 EAA 的 30.6±3.4%、27.4±3.2%、31.3±3.4%、37.2±3.2%、26.4±3.2%、37.8±3.2%和 33.5±3.2%（±标准误差）。利用之前估计的第一次通过时内脏组织 8.27%的 EAA 利用率，从肠道腔吸收的总瘤胃未降解蛋白 EAA 分别为每个成分中 EAA 的 33.4%、29.9%、34.1%、40.6%、28.8%、41.2%和 36.5%。
