富丽霞^1,2, 马涛¹, 刁其玉^,1, 成述儒², 宋雅喆¹, 孙卓琳¹1 中国农业科学院饲料研究所/农业部饲料生物技术重点试验室,北京100081
2 甘肃农业大学动物科学技术学院,兰州 730070

Establishment of a Prediction Model of Metabolizable Protein of Concentrate for Mutton Sheep

FU LiXia^1,2, MA Tao¹, DIAO QiYu^,1, CHENG ShuRu², SONG YaZhe¹, SUN ZhuoLin¹ 1 Key Laboratory of Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute of Chinese Academy of Agricultural Sciences, Beijing 100081
2 College of Animal Science and Technology, Gansu Agriculture University, Lanzhou 730070

通讯作者: 刁其玉,Tel：13910616460;E-mail： diaoqiyu@caas.cn

收稿日期:2018-02-12接受日期:2018-12-29网络出版日期:2019-02-13

基金资助:

国家重点研发计划.2016YFE0109000 国家肉羊产业技术体系建设专项资金.CARS-38

Received:2018-02-12Accepted:2018-12-29Online:2019-02-13
作者简介 About authors
富丽霞,Tel：15711427055;E-mail：fulixia0202@126.com。








摘要
目的 在通过概略养分或可消化养分建立肉用绵羊常用精饲料可代谢蛋白质（metabolic protein, MP）的预测模型,为动物日粮的科学配置提供依据。方法 试验选用14月龄,平均体重为（49.27±3.12）kg的安装有永久性瘤胃瘘管的杜寒杂交1代肉用羯羊6只,采用尼龙袋法和改进三步体外法测定10种精饲料的瘤胃有效降解率、瘤胃非降解蛋白质（undegraded dietary protein, UDP）及UDP小肠消化率;另外选用10只体况健康、平均体重（47.43±4.41）kg的杜寒杂交成年公羊分11期进行消化代谢试验,设11个处理组,其中1个基础饲粮组和10个试验饲粮组,试验组饲粮分别由高粱、玉米、大麦、小麦、燕麦、菜籽粕、花生粕、棉籽粕、豆粕及玉米酒糟（distillers dried grains with solubles, DDGS）等替换基础饲粮中羊 草、玉米和豆粕,每个处理10个重复,每个重复1只羊,每期饲喂20 d,其中预试期15 d,正试期5 d。试验羊提前打好耳号,使用伊维菌素进行驱虫,单栏饲养。由于各组饲粮营养成分存在差异造成采食量不同,在预饲期观察并确定最低组的采食量作为限喂量,每天饲喂两次,分别于8:00、16:30饲喂,每次饲喂600 g,自由饮水。采用全收粪尿法测定养分表观消化率和尿嘌呤衍生物法（purine derivative,PD）测定微生物合成蛋白质（microbial synthetic protein, MCP）,通过养分含量或可消化养分建立MP的预测模型。试验数据采用SAS 9.1中的NLIN程序计算a、b、c值和直线回归与多元回归程序分析建立MP估测模型,单因素方差分析（one-way ANOVA, LSD）进行显著性检验。结果 饲料的粗蛋白质（CP）瘤胃降解率和UDP小肠消化率均因饲料种类不同而异,高蛋白饲料的CP瘤胃降解率和UDP小肠消化率较高,10种精饲料的CP瘤胃有效降解率的范围在43.71%—60.87%之间,UDP小肠消化率的范围在80.10%—92.86%之间,其中燕麦饲料的瘤胃有效降解率显著高于其他9种饲料 (P＜0.001),而其UDP小肠消化率显著低于其他9种饲料 (P＜0.001);饲粮组成不同,各营养物质的表观消化率不同;瘤胃可降解蛋白质与瘤胃非降解蛋白质比例的变化,不会对全消化道养分的表观消化率产生显著影响;本研究中10种饲料的MP与DP的比例范围在50.96%—62.33%之间,基于饲粮CP（%）含量预测可消化蛋白质（DP,%）的模型是DP=0.895×CP-2.663（R²=0.994,n=10,P＜0.001）;基于养分含量（%）和可消化养分（%）建立的MP（g·kg ^-1 DM）预测模型分别是：MP=5.323×CP-14.374 (R²=0.994,n=10,P＜0.001)和MP=5.899×DP+2.077 (R²=0.984,n=10,P＜0.001)。 结论 饲粮中的粗蛋白质含量与可消化蛋白质存在强相关性;饲粮中概略养分含量和可消化养分与MP存在相关性,可以通过饲粮概略养分含量或可消化养分比较准确地估测精饲料的MP值。
关键词： 肉用绵羊;精饲料;微生物合成蛋白质;小肠消化率;可代谢蛋白质;预测模型

Abstract
【Objective】 The aim of this study was to establish a predictive model of metabolizable protein (MP) of concentrates, which is commonly used in feedstuffs of sheep by nutrient or nutrient digestibility. 【Method】 Six 14-month-old Dorper (♂) × thin-tailed Han sheep (♀) sheep with an average body weight of (49.27±3.12) kg fitted with a permanent rumen fistula were selected and used in testing effective degradation rate, rumen undegraded dietary protein (UDP) and intestinal digestibility of UDP by nylon bag method and three-step modified in vitro method. Ten healthy Dorper × thin-tailed Han ram with an average body weight of（47.43±4.41）kg were selected and used in 11 treatment groups including one basic diet group and 10 experimental groups（The Chinese wildrye hay, corn and soybean meal of basic diet were replaced by sorghum, corn, barley, wheat, oat, rapeseed peanut, cottonseed, soybean and DDGS.), respectively. Each period lasted for 20 d (15 d for adaptation and 5 d for trial period). The experimental sheep were prefixed with ear numbers, dewormed with ivermectin, and feed a single column. Due to the differences in the nutrient composition of each group of feeding foods, the amount of feeding in the lowest group was observed and determined during the adaptation as the limit of feeding, fed twice a day, at 8:00 and 16:30, respectively. Feed 600 g, free drinking water. Each ram is a replicate and all rams were used to determine the apparent digestibility of nutrients and microbial synthetic protein (MCP) using the urinary purine derivative method. The MP predictive model was established using proximal analysis of nutrient contents or nutrient digestibility. Using NLIN program in SAS 9.1 to calculate a, b, c values and linear regression and multivariate regression program analysis, MP estimation model was established, and the single factor variance analysis(one-way ANOVA, LSD) was significantly tested. 【Result】 The results showed that the rumen digestibility and digestion rate of CP in different concentrates were different, and CP degradability and intestinal digestibility of UDP of high protein diet were higher. The effective degradation rate of CP rumen in 10 kinds of feed ranged from 43.71% to 60.87%, and intestinal digestibility of UDP ranged from 80.10% to 92.86%. The effective degradation rate of rumen in oat feed was significantly higher than that of other feeds (P＜0.001), while intestinal digestibility of UDP was significantly lower than that of other feeds (P＜0.001). The diets had different composition and apparent digestibility of different nutrients. The digestion and absorption sites of dietary protein did not affect the apparent digestibility of nutrients. The ratio of MP to DP of 10 feeds in this study ranged from 50.96% to 62.33%, The digestible protein (DP, %) prediction model established by dietary CP (%) content was：DP=0.895×CP-2.663 (R²=0.994, n=10, P＜0.001); The MP (g·kg ^-1 DM) prediction model established by nutrient contents (%) and apparent nutrient digestibility (%) were: MP=5.323×CP-14.374 (R²=0.994, n=10, P＜0.001) and MP=5.899×DP+2.077 (R²=0.984, n=10, P＜0.001).【Conclusion】 Digestible protein had a strong relationship with crude protein in diet. The nutrient content and nutrient digestibility in diets were correlated with the presence of MP, and the MP values of concentrate feed could be estimated more accurately by the nutrient and nutrient digestibility in diets.
Keywords：mutton sheep;concentrate;microbial synthetic protein;small intestinal digestibility;metabolizable protein;prediction model


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本文引用格式
富丽霞, 马涛, 刁其玉, 成述儒, 宋雅喆, 孙卓琳. 肉羊精料可代谢蛋白质预测模型的建立[J]. 中国农业科学, 2019, 52(3): 539-549 doi:10.3864/j.issn.0578-1752.2019.03.014
FU LiXia, MA Tao, DIAO QiYu, CHENG ShuRu, SONG YaZhe, SUN ZhuoLin. Establishment of a Prediction Model of Metabolizable Protein of Concentrate for Mutton Sheep[J]. Scientia Agricultura Sinica, 2019, 52(3): 539-549 doi:10.3864/j.issn.0578-1752.2019.03.014

0 引言

【研究意义】反刍动物由于瘤胃特殊的消化生理结构,单从饲粮概略养分含量或可消化养分很难准确地评价饲粮的真实饲用价值,必须结合营养物质在体内的一系列生化转化过程才能客观完整地反映对饲粮的利用效果。可代谢蛋白质（MP）是目前评价反刍动物利用饲粮蛋白质最准确的指标,该指标不仅考虑了动物本身对饲粮蛋白质的需要,还将瘤胃微生物对饲粮蛋白质的利用情况考虑在内,比较充分完整地体现了反刍动物利用蛋白质的特殊性。准确估测饲粮中的MP,可以简捷快速地评价饲粮的营养价值,为饲粮间配合效果提供科学依据。【前人研究进展】MP的准确测定比较复杂,一方面要测定瘤胃微生物合成蛋白质（MCP）,还要明确原料瘤胃非降解蛋白质（UDP）在小肠中的代谢情况。测定MCP应用最广泛最经典的方法是标记物法,其中尿嘌呤衍生物（PD）法测定步骤简单,符合动物福利要求,是估测MCP最有效的方法之一,MA等^[1,2]应用该法探究了单一饲粮中尿嘌呤衍生物与微生物氮的估测模型。AFRC ^[3]中报道MCP中有25%表现为核酸的形式,不能用于体组织的组成,而剩余的75%的MCP在小肠中的消化率约为85%,因此MCP在小肠中的消化率约为64%。关于UDP及其小肠消化率的测定主要采用尼龙袋法和改进三步体外法,该方法简单易于操作,并且很好的模拟了反刍动物特殊的生理条件,GARGALLO 等^[4]采用改进三步体外法测定了12种饲料的UDP小肠消化率,王燕等^[5]综合比较发现改进三步体外法可以比较准确的测定UDP小肠消化率。国外****（INRA,1989;AFRC,1993;CSIRO,2007;NRC,2007）对MP体系的研究较多^[3,6-8],认为MP与DP显著相关,但是国外的相关模型并不一定适合中国的实际生产及相关品种,近年来国内****对该体系的研究已经展开^[9,10],但是只研究了不同精粗比饲粮的MP预测模型,饲料来源比较单一。【本研究切入点】精饲料是提供饲粮蛋白质的主要原料,反刍动物由于其消化生理结构的特殊性不能饲喂单一精饲料,并且我国地域辽阔,精饲料种类繁多,赵江波等^[11]研究了肉羊常用精饲料代谢能的预测模型,对于肉用绵羊常用精饲料可代谢蛋白质的研究鲜见报道,因此本研究考虑应用套算法探索肉用绵羊对不同精饲料原料的蛋白质利用情况。【拟解决的关键问题】通过实测各种饲粮的概略养分含量和进行消化代谢试验得到各种养分在体内的消化代谢实测数据,建立肉用绵羊常用精饲料的MP估测模型,从而可利用简单的化学分析或消化参数预测饲粮中的MP,简捷快速地评价各种饲粮的营养价值,为进一步完善我国肉用绵羊的饲养标准提供参考。

1 材料与方法

1.1 试验时间和地点

本试验于2016年10月11日至2017年6月12日在中国农业科学院南口中试基地进行。

1.2 试验材料

尿囊素：纯度≥98.0%（Sigma）,尿酸：纯度≥99.0%（Sigma）,黄嘌呤氧化酶：7.6 unit/mL（Sigma）,尿酸酶：5 unit/mg（Sigma）,胃蛋白酶（Sigma P-7000）,胰蛋白酶（Sigma P-7545）,百里香酚。

1.3 试验动物与试验设计

选用14月龄体况健康,平均体重为（49.27±3.12）kg的安装有永久性瘤胃瘘管的杜泊羊（♂）×小尾寒羊（♀）杂交1代肉用羯羊6只,进行尼龙袋试验和改进三步体外法试验,饲粮组成及营养水平见表1。


Table 1
Table 1Composition and nutrient levels of the diet for nylon bag test and three-step modified in vitro test (Dry matter basis, %)

项目 Items	含量 Content
原料 Ingredients
羊草 Chinese wildrye hay	55.00
玉米 Corn	29.40
豆粕 Soybean meal	14.00
磷酸氢钙 CaHPO4	0.86
食盐 NaCl	0.50
预混料Premix1)	0.24
合计 Total	100
营养水平 Nutrient levels2)
干物质 Dry matter, DM	95.55
有机物 Organic matter, OM	93.68
总能 Gross energy, GE（MJ·kg-1）	16.34
粗蛋白质 Crude protein, CP	11.90
中性洗涤纤维 Neutral detergent fiber, NDF	59.12
酸性洗涤纤维 Acid detergent fibre, ADF	25.22
粗脂肪 Ether digestible organic matter extract, EE	2.21
钙 Ca	0.93
磷 P	0.41

¹⁾ 预混料为每千克饲粮提供The premix provides the following per kg of diet: VA 15 000 IU,VD 5 000 IU,VE 50 mg,Fe 90 mg,Cu 12.5 mg,Mn 60 mg,Zn 90 mg,Se 0.3 mg,I 1.0 mg,Co 0.3 mg
²⁾ 营养水平均为实测值 The nutrient levels are measured values

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选用另外10只体况健康,平均体重（47.43±4.41）kg的杜寒杂交成年公羊进行消化代谢试验,采用单因子试验设计,试验分11期处理,其中：1期基础饲粮组和10期试验饲粮组,每期处理10个重复,每个重复1只羊。试验饲粮组分别由10种肉用绵羊常用的精饲料高粱、玉米、大麦、小麦、燕麦、菜籽粕、花生粕、棉籽粕、豆粕及玉米酒糟DDGS等替换基础饲粮中羊草、玉米和豆粕,单一精饲料替换比例为30%^[12],饲粮组成及营养水平见表2。


Table 2
Table 2Dietary composition and nutrient levels (DM basis, %)

项目 Items	组成 Ingredient
	基础 饲粮 Basal diet	高粱 饲粮 Sorghum diet	玉米 饲粮 Corn diet	大麦 饲粮Barley diet	小麦 饲粮Wheat diet	燕麦 饲粮 Oat diet	菜籽粕 饲粮Rapeseed diet	花生粕 饲粮 Peanut meal diet	棉籽粕 饲粮Cottonseed meal diet	豆粕 饲粮Soybean meal diet	玉米酒 糟饲粮 DDGS diet
不同精料替换比例 Different concentrate replacement ratio		30.0	30.0	30.0	30.0	30.0	30.0	30.0	30.0	30.0	30.0
玉米corn	19.0	13.2	13.2	13.2	13.2	13.2	13.2	13.2	13.2	13.2	13.2
豆粕Soybean mean	12.2	8.46	8.46	8.46	8.46	8.46	8.46	8.46	8.46	8.46	8.46
羊草Chinese wildrye hay	66.5	46.0	46.0	46.0	46.0	46.0	46.0	46.0	46.0	46.0	46.0
磷酸氢钙CaHPO4	1.41	1.41	1.41	1.41	1.41	1.41	1.41	1.41	1.41	1.41	1.41
石粉Limestone	0.15	0.15	0.15	0.15	0.15	0.15	0.15	0.15	0.15	0.15	0.15
食盐NaCl	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50
预混料Premix1）	0.24	0.24	0.24	0.24	0.24	0.24	0.24	0.24	0.24	0.24	0.24
合计Total	100	100	100	100	100	100	100	100	100	100	100
营养水平Nutrient levels2）
干物质DM	92.13	90.92	90.79	91.62	91.51	91.58	91.87	91.55	93.96	93.89	91.32
有机物OM	90.15	93.10	93.45	93.77	93.51	94.74	89.06	89.38	92.34	92.07	90.30
总能 GE (MJ·kg-1)	17.92	17.78	17.81	17.75	17.63	17.93	18.25	18.40	18.43	18.21	18.81
粗蛋白质CP	12.03	11.06	10.56	11.50	11.96	12.68	22.12	26.89	20.36	22.55	17.06
中性洗涤纤维NDF	33.20	33.56	33.33	37.84	37.15	33.29	40.13	36.19	41.33	33.55	40.74
酸性洗涤纤维ADF	18.05	17.71	16.82	19.66	19.03	17.43	22.35	19.44	23.67	19.67	19.42
粗脂肪EE	2.70	2.16	2.19	2.01	2.24	2.77	2.04	1.13	1.40	1.65	3.89
灰分 Ash	9.85	6.90	6.55	6.23	6.49	5.26	10.94	10.62	7.66	7.93	9.70
钙 Ca	0.94	1.05	0.94	0.82	0.96	0.96	1.45	1.06	1.03	0.99	0.82
总磷 TP	0.35	0.24	0.29	0.25	0.26	0.29	0.36	0.27	0.32	0.31	0.39

^1）预混料每千克饲粮提供The premix provides the following per kg of diet: VA 12 000 IU, VD 5 000 IU, VE 50 IU, Fe 60 mg, Cu 16.0 mg, Mn 40 mg, Zn 70 mg, I 0.8 mg, Se 0.3 mg, Co 0.3 mg
^2）营养水平为实测值。The nutrient levels are measured values

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1.4 饲养管理

试验羊用耳号标记,用伊维菌素进行驱虫,单栏饲养。6只试验瘘管羯羊提前饲喂基础日粮（表1）15 d,再进行尼龙袋试验和改进三步体外法试验。

10只试验公羊饲喂基础饲粮组和10种试验饲粮组（表2）,各组饲粮营养成分存在差异造成采食量不同,为消除差异通过预饲期观察,确定最低组的采食量作为饲喂量^[13],每天分别于8：00、16：30饲喂,饲喂量600 g,自由饮水,每种饲粮饲喂20 d,其中预试期15 d,正试期5 d,正试期全收粪和尿。

1.5 半体内试验（尼龙袋试验）

试验单一饲料为10种反刍动物常用的精饲料：高粱、玉米、大麦、小麦、燕麦、菜籽粕、豆粕、棉籽粕、花生粕和DDGS,饼粕类饲料的加工方法都采用行业的浸提法,玉米等谷物类采用粉碎机直接粉碎粒度5 mm左右,DDGS由于本身颗粒小,购买后直接使用,经2.5 mm筛孔的粉碎机粉碎。

采用HVELPLUND^[14]尼龙袋法测定10种精饲料原料的瘤胃降解率,每个样品设立3个重复,每个重复1只羊。样品设6、12、24、36、48 h等5个时间点,每个时间点2个平行。准确称取试验样品6 g,放入已恒重的尼龙袋中,2个平行的尼龙袋绑在一个塑料管上。饲喂后2 h投放至瘤胃,不同时间点分别投放,最后统一取出。自来水冲洗干净（0时间点的也需要一起冲洗）,置于鼓风干燥箱内65℃下恒温烘48 h,回潮24 h后称重。测定分析其中的DM、OM、CP。

1.6 改进三步体外法试验

采用改进三步体外法^[4]测定UDP小肠消化率。称取5 g试验样品于尼龙袋中,置于瘤胃中培养16 h后取出,清洗至水清,在55℃烘箱内烘48 h,制成风干样后过40目筛,称取0.5 g经瘤胃16 h降解后的饲料残渣风干样,放入Ankom F57滤袋中,用封口机封口。将来自同一只羊的30个滤袋（即5个饲料样品×6个重复）放入同一个培养品中,每个培养品加入预培养的盐酸胃蛋白酶溶液2升[每升溶液中含有1g胃蛋白酶（Sigma P-7000）,用0.1 N HCl调节pH至1.9],将培养瓶置于Daisy II（Ankom,Fairport,NY,USA）培养箱39℃振荡培养1 h后,用自来水冲洗尼龙袋至水澄清。再次将滤袋放入含有预热的胰酶制剂溶液[每升溶液中含50 mg百里香酚,3 g胰酶制剂（Sigma P-7545）,用磷酸二氢钾调节pH至7.75]的培养瓶中于39℃震荡培养24 h,用自来水冲洗尼龙袋至水澄清,55℃烘干至恒重,称重,分析袋内残渣总蛋白含量。

1.7 消化代谢试验及样品收集

每期消化代谢试验正试期前后均称重并记录。

正试期每天全收粪并称重,将粪样充分混匀并从不同位点取未受羊毛及尘土污染的部分样品,准确称取总粪量的10%于自封袋中置于-20℃冰箱保存;每天全收尿并记录尿量,收尿前于桶中加入100 mL 10%的稀硫酸,调整尿样pH至2—3,防止尿样腐败分解,四层纱布过滤,采集尿样时先加自来水将尿样稀释至5 L,混匀后取30 mL尿样于收尿瓶中置于-20℃冰箱保存。

1.8 测定指标

样品中营养成分DM、OM、CP、Ash的测定参照张丽英^[15]的测定方法,测定NDF和ADF含量时,先用胰蛋白酶及淀粉酶对样品进行酶解处理,再按照VAN SOEST等^[16]方法进行操作。PD采用分光光度计进行测定^[17]。

1.9 计算公式

1.9.1 待测样品在不同时间点的瘤胃消失率及有效降解率（effective degradation rate, ED）的计算公式

A（%）=100×（B-C）/B

式中,A为待测饲料营养物质的瘤胃消失率（%）;B为待测样品中营养物质的质量（g）;C为残渣中营养物质的质量（g）。

有效降解率参照ORSKOV 和 MC DONALD 提出的数学模型^[18]计算：

dP = a + b(1 - e^-ct)

式中,dP为某营养成分在t时间的瘤胃消失率;a = 快速降解部分（%）;b = 慢速降解部分（%）;c = b部分的降解速率（/h）;t = 培养时间（h）。

利用最小二乘法算出参数a、b和c,然后进一步计算有效降解率：ED = a + bc/(c + k)

式中,ED为某营养成分的有效降解率;k为待测饲料的流通速率,参考冯仰廉^[19]取K=0.08%/h。

1.9.2 UDP小肠消化率计算

UDP（%）= CP含量（%）×（1-瘤胃CP降解率）;

UDP小肠消化率（%）=（UDP含量-残渣中蛋白质含量）/UDP含量×100。

1.9.3 营养物质消化率及PD排出量等指标的计算

饲粮中某营养成分的表观消化率（%）= 100×（饲粮采食量×饲粮中该营养成分的含量-排粪量×粪中该养分含量）/（饲粮采食量×饲粮中该营养成分的含量）;

PD（mmol·d^-1）=尿囊素+尿酸+黄嘌呤+次黄嘌呤,微生物氮 (Microbial nitrogen, MN, g·d^-1) =-0.521+ 1.493×PD (mmol·d^-1)^[1];

MP=MCP×0.64+UDP×UDP小肠消化率^[3]。

1.10 统计分析

试验数据采用Excel整理统计后,分别采用SAS 9.1中的NLIN程序计算a、b、c值和直线回归与多元回归程序分析建立MP估测模型,单因素方差分析（one-way ANOVA, LSD）进行显著性检验,并采用Duncan氏法进行多重比较,P＜0.05作为差异显著的判断标准。结果均以平均值表示。

2 结果

2.1 单一精饲料原料的常规养分含量

本试验中10种单一精饲料原料的常规养分含量见表3,各种饲料CP含量差异较大,饼粕类饲料的CP较高,DDGS次之,谷物类饲料最低。

Table 3
表3
表3单一精饲料原料的营养水平（干物质基础）
Table 3Concentrates nutrient levels (DM basis) (%)

项目 Items	高粱Sorghum	玉米 Corn	大麦 Barley	小麦 Wheat	燕麦 Oat	菜籽粕 Rapeseed meal	花生粕 Peanut meal	棉籽粕 Cottonseed meal	豆粕Soybean meal	玉米酒糟DDGS
干物质 DM	89.59	89.94	90.60	89.64	90.31	91.60	91.97	92.28	91.74	91.65
有机物 OM	98.27	98.79	95.75	98.33	98.22	93.04	94.39	92.66	92.50	95.19
粗蛋白 CP	10.48	8.88	10.35	13.57	15.15	40.50	58.36	44.99	47.92	30.45
中性洗涤纤维 NDF	14.97	16.98	18.58	14.87	10.25	17.45	12.24	20.17	12.93	23.97
酸性洗涤纤维 ADF	3.01	4.06	8.69	4.66	3.30	13.19	6.65	14.60	7.05	8.66

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2.2 单一精饲料原料CP瘤胃降解率和UDP小肠消化率

采用尼龙袋法和改进三步体外法及基于公式（1.9.1和1.9.2）得出的CP瘤胃降解率和UDP小肠消化率见表4。可以看出,10种饲料的CP有效降解率在43.71%—60.87%之间,其中燕麦的CP瘤胃有效降解率显著高于其他9种饲料（P＜0.01）,除燕麦外,本研究的其他9种饲料中饼粕类饲料（菜籽粕、花生粕、棉籽粕、豆粕、DDGS）的CP瘤胃有效降解率均高于谷物类饲料（高粱、玉米、大麦、小麦）;而燕麦的UDP小肠消化率为80.10%,显著低于其他饲料（P＜0.01）,饼粕类饲料的UDP小肠消化率均高于谷物类饲料。

Table 4
表4
表4单一精饲料蛋白质瘤胃降解率和瘤胃非降解蛋白质小肠消化率
Table 4Ruminal degradability of crude protein and intestinal digestibility of undegraded dietary protein of concentrates (%)

项目 Items	高粱Sorghum	玉米Corn	大麦 Barley	小麦 Wheat	燕麦 Oat	菜籽粕 Rapeseed meal	花生粕 Peanut meal	棉籽粕 Cottonseed meal	豆粕Soybean meal	玉米 酒糟DDGS	SEM	P值 P value
蛋白质瘤胃降解率 Ruminal degradability of crude protein
6 h	16.64d	24.25bcd	22.73cd	30.30b	44.30a	27.42bc	24.33bcd	29.19b	16.87d	15.77d	1.697	＜0.01
12 h	20.10d	27.54cd	31.66cd	49.83b	63.53a	35.55c	28.63cd	31.53cd	20.28d	19.73d	2.649	＜0.01
24 h	24.82c	32.77bc	39.66b	63.25a	72.64a	41.34b	40.82b	42.52b	34.15bc	22.15c	2.948	＜0.01
36 h	36.18cd	37.66cd	48.51bc	70.28a	80.64a	47.56bc	48.55bc	54.55b	41.45bcd	35.03d	3.302	＜0.01
48 h	38.77d	47.25cd	59.36bc	74.27a	84.19a	58.01bc	59.51bc	62.18b	54.02bc	38.88d	2.668	＜0.01
有效降解率Effective degradation rate	45.08e	43.71e	44.38e	49.32de	60.87a	52.04bcd	57.26ab	54.62bcd	56.02abc	51.08cd	1.143	＜0.01
瘤胃非降解 蛋白质小肠消化率 Small intestine digestibility of undegraded dietary protein	84.69d	86.23cd	84.23d	84.10d	80.10e	89.25b	92.86a	92.31a	89.26b	87.31bc	0.731	＜0.01

In the same row, values with different small letters mean significant difference (P＜0.05). The same as below
同行数据标不同小写字母表示差异显著(P＜0.05)。下表同

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2.3 单一精饲料可代谢蛋白质

小肠吸收的蛋白质主要由MCP和UDP组成,通过半体内法（尼龙袋法）及公式（1.9.1和1.9.2）得出单一精饲料的瘤胃降解蛋白质（Rumen degraded protein,RDP）和UDP,利用尿嘌呤衍生物法及结合公式（1.9.3）得出单一精饲料的MCP,进一步通过公式MP=MCP×0.64+UDP×UDP小肠消化率（AFRC,1993）得出单一精饲料MP（表5）。由表5可见,10种精饲料RDP从高到低的顺序依次是花生粕、豆粕、棉籽粕、菜籽粕、DDGS、燕麦、小麦、高粱、大麦及玉米;本研究的10种精饲料的UDP含量除燕麦和小麦外,各饲料UDP含量从高到低的顺序与RDP的顺序一致;饼粕类饲料的MCP和MP均高于谷物类的,MCP含量在46.92—84.74（g·kg^-1 DM）之间,MP含量在41.81—129.08（g·kg^-1 DM）之间,其中花生粕的MCP和MP都最高,玉米的MCP和MP都最低。MP占DP的比例范围在50.96%—62.33%之间。

Table 5
表5
表5单一精饲料原料的瘤胃非降解蛋白质、微生物合成蛋白质和可代谢蛋白质
Table 5Undegraded dietary protein, microbial synthetic protein and metabolizable protein of concentrates

项目 Items	高粱 Sorghum	玉米 Corn	大麦 Barley	小麦 Wheat	燕麦 Oat	菜籽粕 Rapeseed meal	花生粕 Peanut meal	棉籽粕 Cottonseed meal	豆粕Soybean meal	玉米 酒糟DDGS
瘤胃降解蛋白质 RDP (g·kg-1 DM)	15.59	12.82	15.15	22.16	30.35	68.84	115.23	79.43	85.76	51.16
瘤胃非降解蛋白质 UDP (g·kg-1 DM)	18.98	16.52	18.74	22.31	19.30	63.44	85.85	64.22	67.34	48.89
微生物合成蛋白质 MCP (g·kg-1 DM)	54.50	46.92	50.97	50.64	59.83	73.80	84.74	66.27	81.11	60.87
可代谢蛋白质 MP (g·kg-1 DM)	48.04	41.81	45.46	48.28	50.30	99.47	129.08	96.89	106.18	78.23
可代谢蛋白质占可消化蛋白的比例 The percentage of MP to DP (%)	61.66	55.63	50.96	55.08	53.73	53.33	54.86	62.33	55.14	56.78

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2.4 10种饲粮营养物质的表观消化率

10种饲粮营养物质的表观消化率见表6,可以看出,不同饲粮各营养物质的表观消化率不同,其中玉米饲粮的DM表观消化率最高,为67.40%,菜籽粕饲粮的DM表观消化率只有57.32%;玉米饲粮的OM表观消化率也最高,菜籽粕饲粮的最低;饼粕类饲粮的CP表观消化率高于谷物类饲料的,CP表观消化率在64.03%—80.16%之间;NDF和ADF的表观消化率范围分别是36.01%—48.79%、34.35%—47.40%。

Table 6
表6
表6不同饲粮营养物质表观消化率
Table 6Apparent nutrient digestibility of different diets (%)

项目 Items	高粱 饲粮 Sorghum diet	玉米 饲粮Corn diet	大麦 饲粮Barley diet	小麦 饲粮 Wheat diet	燕麦 饲粮 Oat diet	菜籽粕 饲粮Rapeseed diet	花生粕 饲粮Peanut meal diet	棉籽粕 饲粮Cottonseed meal diet	豆粕 饲粮Soybean meal diet	玉米酒糟饲粮 DDGS diet	SEM	P值 P value
干物质消化率 Digestible dry matter (DMD)	65.29abc	67.40a	64.69bc	65.48abc	63.40c	57.32e	64.20c	59.68d	66.79ab	58.78de	0.41	＜0.01
有机物消化率 Digestible organic matter (DOM)	68.65ab	70.44a	68.49ab	68.68ab	66.91b	64.15c	69.97a	61.45d	69.30a	64.47c	0.37	＜0.01
粗蛋白质消化率 Digestible crude protein (DCP)	64.03e	64.60de	71.05b	67.09cd	67.63c	77.47a	79.73a	71.75b	80.16a	73.76b	0.65	＜0.01
中性洗涤纤维消化率 Digestible neutral detergent fiber (DNDF)	42.96bc	42.56bcd	47.59ab	48.79a	38.86cde	37.09de	43.71abc	36.01e	42.66bcd	41.67cd	0.67	＜0.01
酸性洗涤纤维消化率 Digestible acid detergent fiber (DADF)	42.91ab	37.38c	45.10a	45.85a	38.46bc	34.35dc	46.96a	30.91d	47.40a	35.91c	0.76	＜0.01

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2.5 可代谢蛋白质预测模型的建立

为进一步通过饲粮养分含量和可消化养分来预测饲料的可代谢蛋白质,结合本试验中10种饲粮的养分含量和可消化养分与MP进行逐步回归分析,建立的回归模型如表7所示。从模型式可见,决定系数R²均在0.98以上,饲料养分含量比可消化养分预测MP决定系数R²更高。基于养分含量建立MP预测模型的预测因子从一元到五元决定系数R²增加幅度不大;引入变量越多,可消化养分预测MP模型的决定系数R²值越高,R²的变化范围在0.984—0.991之间。用饲粮中CP含量预测DP,决定系数R²为0.984。

Table 7
表7
表7概略养分和可消化养分预测可代谢蛋白质模型
Table 7Prediction model for metabolizable protein using chemical composition and apparent digestibility

递推回归模型Recursive regression equation	决定系数 R2	P值 P value
MP=5.323CP-14.374	0.994	＜0.001
MP=5.268CP+0.532DM-62.319	0.995	＜0.001
MP=5.290CP+0.669DM-0.173ADF-71.664	0.995	＜0.001
MP=5.318CP+1.262DM-0.877ADF+0.376NDF-126.679	0.995	＜0.001
MP=5.373CP+1.481DM-0.827ADF+0.404NDF+0.254OM-174.198	0.995	＜0.001
MP=5.899DP+2.077	0.984	＜0.001
MP=5.710DP-0.530DOM-37.165	0.986	＜0.001
MP=5.500DP-1.741DOM+1.371DDM+38.005	0.989	＜0.001
MP=5.678DP-1.550DOM+1.344DDM-1.129DNDF+32.093	0.990	＜0.001
MP=5.791DP-1.587DOM+1.552DDM-1.871DNDF+0.443DADF+19.832	0.990	＜0.001
DP=0.895CP-2.663	0.994	＜0.001

Prediction equations are based on the measured nutrient content and digestible nutrient content of 10 feeds. MP is a metabolizable protein (g·kg^-1 DM); the unit of proxinate nutrient is % and the unit of digestible nutrient is %
预测模型基于10种饲料养分含量和可消化营养成分的实测值。MP为可代谢蛋白质（g·kg^-1 DM）;概略养分的单位为%,可消化养分的单位是%

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3 讨论

3.1 单一精饲料粗蛋白质瘤胃降解率和小肠消化率

关于精饲料CP瘤胃降解率和UDP小肠消化率已有较多研究^{[20,21,22,23]}。饲料在瘤胃中的降解主要是瘤胃微生物的一系列生物消化过程,一般而言,随饲料在瘤胃中停留时间的增加,瘤胃降解率增大,饲料自身的物理或化学性质也会影响瘤胃降解率^[24,25]。本研究的10种精饲料中,燕麦因其包被淀粉粒的蛋白质基质很容易被细菌穿透,所以CP瘤胃降解率显著高于其他饲料,其他几种饲料中饼粕类饲料（菜籽粕、花生粕、棉籽粕、豆粕、DDGS）的CP瘤胃降解率高于谷物类饲料（高粱、玉米、大麦、小麦）,这可能与饼粕类饲料含有较高的CP含量有关,冷静等^[26]通过研究6种牧草的瘤胃降解率发现CP含量高有利于蛋白质的降解。饲料CP含量高,能够为瘤胃微生物提供的氮源丰富,因此相应的CP瘤胃降解率会长高。另一方面,过高的瘤胃消失率将会造成进入反刍动物小肠的蛋白质不足,因此CHALUPA 等^[27]认为应当对瘤胃降解较高的饲料采取过瘤胃保护措施（如热处理和甲醛处理）,以保证小肠有充足的可吸收利用氨基酸。

本研究得出10种精饲料的UDP小肠消化率范围在80.10%—92.86%之间,在INRA报道的65%—95%范围内^[7]。比较发现每种饲料的UDP小肠消化率均高于CP瘤胃降解率,表明大量不被瘤胃降解的蛋白质能在小肠被很好的消化,朱亚骏等^[22]得出类似的结果,因此可以考虑使用这10种饲料做蛋白质过瘤胃保护措施,以提供给小肠充足的氨基酸。本研究还发现饼粕类饲料（菜籽粕、花生粕、棉籽粕、豆粕、DDGS）的UDP小肠消化率高于谷物类饲料（高粱、玉米、大麦、小麦,燕麦）,周荣等^[23]报道奶牛对常用饲料的UDP小肠消化率饼粕类饲料最高,谷物类饲料次之,粗饲料最低,岳群等^[28]研究发现高蛋白低纤维饲料比低蛋白高纤维饲料更易被小肠消化利用,本试验中使用的饼粕类饲料较谷物类饲料蛋白质含量高很多,而纤维含量相差不大,据此可认为精饲料蛋白质含量越高,UDP小肠消化率越高,与周荣等^[23]和岳群等^[28]研究的结果相一致。

3.2 饲粮养分表观消化率和精饲料瘤胃微生物蛋白质合成量

营养物质的表观消化率是动物对饲粮消化利用的综合反映,本试验中10种饲粮因其精饲料组成不同,各养分表观消化率差异显著,其结果与赵江波等^[12]在杜寒杂交羯羊的研究结果接近。10种饲粮精饲料组成不同,饼粕类饲粮的CP水平高于谷物类饲粮,随CP水平的增加,CP表观消化率有升高的趋势,但其他养分的表观消化率没有明显的变化,与李志静等^[29]研究得出的结果类似,刘洁等^[13]研究表明CP表观消化率与CP含量存在正相关关系。纤维是影响反刍动物采食量的一个重要因素,在瘤胃中发酵的产物是其重要的能量来源,NDF是目前认为表示纤维含量的最准确的指标,本研究中10种饲粮的NDF水平在33.33%—41.33%范围内,通过比较发现,NDF含量对其他营养物质的表观消化率无显著影响,孔祥浩等^[30]报道肉羊饲粮的NDF含量处于30%—45%之间时,对其他营养物质的表观消化率影响不显著。

本研究中10种精饲料的RDP、UDP、MP含量以及MCP合成量,饼粕类饲料均高于谷物类饲料。瘤胃微生物利用饲粮中养分降解产生的氮源与碳源合成微生物蛋白质,饲粮蛋白质含量越高,提供给微生物的氮源越丰富,微生物合成蛋白质越多,最终以MP含量的多少体现反刍动物对饲粮蛋白质的利用效果,MA等^[1]研究报道饲粮中CP含量越高,NDF含量越低,MCP合成量越高。本研究得出随着饲粮中RDP水平的增加,MCP含量也增加,与HAIG等^[31,32]通过十二指肠MCP流量和尿嘌呤衍生物法研究得出的结果类似。随着10种精饲料原料的RDP与UDP比例的增加,各养分的表观消化率没有表现出明显的变化趋势,PAENGKOUM^[33]等也报道饲粮养分消化率不受RDP含量的影响。反刍动物采食的饲粮蛋白质,必须有一定量的RDP供微生物分解利用,否则就会调用体蛋白为细菌提供营养,使机体的代谢形成负平衡,若细菌营养不足,也会影响淀粉和纤维素的消化。

3.3 利用饲粮养分含量和可消化养分建立精饲料原料MP的预测模型

蛋白质不仅是饲粮重要的营养成分,也是限制肉用绵羊生产性能的重要因素,饲粮中被动物机体利用的蛋白质除了受机体自身的影响外,还受到饲粮组成及可消化养分的影响。综合10种饲粮的概略养分及可消化养分与MP进行相关性分析,并建立递推式回归模型,发现引入概略养分含量建立的MP预测模型决定系数比利用可消化养分得到的决定系数高。当只引入CP含量时,R²就已经达到0.994,再依次引入DM、ADF、NDF和OM时,R² 升高。如果采用可消化养分建立MP预测模型,可以看出依次引入可消化养分参数,R²不断提高,从0.984升高至0.991,预测模型的显著效果未发生变化。

本研究利用饲粮中CP含量（%）及DP（%）建立的MP（g·kg^-1 DM）预测模型分别是MP=5.323× CP-14.374（R²=0.994,n=10,P＜0.001）和MP=5.899× DP+2.077 (R²=0.984,n=10,P＜0.001),经转化发现MP预测模型与NRC（2007）推荐的MP（%）=0.7×DP（%）有差异,可能与羊的品种及饲料的地域性有关。基于CP建立的DP预测模型是 DP=0.895×CP-2.663（R²=0.994,n=10,P＜0.001）,与NRC（2007）的DP =0.9×CP-3及刘洁^[9]的DP=1.000×CP-4.672结果接近。刘洁^[9]建立了单一饲粮12个不同精粗比梯度的MP预测模型：MP（g·kg^-1DM）=-55.712 + 9.826×CP（%）和MP（g·kg^-1 DM）=-9.841+0.983×DP（g·kg^-1DM）,曲连发^[10]建立了单一饲粮6个不同精粗比梯度的MP预测模型：MP（g·kg^-1 DM）= 0.96×CP（g·kg^-1 DM）-87.89和MP（g·kg^-1DM）=0.75×DP（g·kg^-1DM）-25.82,两个研究结果都得出MP与CP或DP的相关性最高,NRC（2007）也推荐采用CP或DP预测MP模型,本研究得出的结果类似。

前人研究均采用一元函数预测MP,但预测模型都有差异,本研究得出10种单一精饲料原料的MP与DP的含量各不相同,范围在50.96%—62.33%之间,因此利用多种饲粮的DP建立MP的预测模型更加准确,利用更加广泛。对于我国肉用绵羊常用精饲料MP的预测模型鲜有报道,通过本研究依次引入多元变量,使预测值的准确性得到了提高,决定系数R²逐渐增大,并对饲料中养分或可消化养分逐一进行方差膨胀因子（VIF）检验,得出VIF均小于10,即各个因子不存在多重共线性,不影响最终MP的预测值。本试验中,根据MP与养分含量和可消化养分之间的相关性建立了关于MP的多个预测模型,并且决定系数很高。通过对各个预测模型进行检验,发现采用养分含量预测MP模型时,得出利用一元或多元建立的MP预测模型得出的MP值与实际值都很接近;引入可消化养分预测MP时,不论引入一元或者多元MP预测结果也都与实际值很接近。表明在实际生产中可以通过简单的测定养分含量或可消化养分就可以估测出肉用绵羊对饲粮中CP的利用效果。

可代谢蛋白质比较准确地反映了反刍动物利用蛋白质的效果,但是测定步骤繁琐,在实际的生产实践中不易测定,本研究通过体外法、半体内法和体内法较为完整的研究了肉用绵羊对常用精饲料蛋白质的利用情况,并基于概略养分和可消化营养成分建立了MP的预测模型,对MP的估测有重要意义。但是由于试验周期较长,还未对预测模型用其他饲粮进行验证,所以还有待于进一步研究,以便更好的完善与推广。

4 结论

4.1

基于饲粮中CP含量预测DP的模型是：DP= 0.895×CP-2.663（R²=0.994,n=10,P＜0.001）。

4.2

基于概率养分可以比较准确的预测MP,预测模型是：MP=5.323×CP-14.374（R²=0.994,n=10,P＜0.001）。

4.3

基于可消化养分建立的精饲料MP预测模型是：MP=5.899×DP+2.077（R²=0.984,n=10,P＜0.001）。

参考文献 View Option 原文顺序
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[22] 朱亚骏, 于子洋, 袁翠林, 胡静, 王利华, 朱风华, 张廷荣, 林英庭 . 山东省羊主要精饲料瘤胃降解率和小肠消化率的研究
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ZHU Y J, YU Z Y, YUAN C L, HU J, WAMG L H, ZHU F H, ZHANG T R, LIN Y T . Research about ruminal and small intestinal digestibility of Shandong province mainly concentrates for sheep
Chinese Agricultural Science Bulletin. 2014,30(17):1-6. (in Chinese)
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[23] 周荣, 王加启, 张养东, 潘发明, 卜登攀, 魏宏阳, 周凌云 . 移动尼龙袋法对常用饲料蛋白质小肠消化率的研究
东北农业大学学报, 2010,41(01):81-85.
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ZHOU R, WANG J Q, ZHANG Y D, PAN F M, BU D P, WEI H Y, ZHOU L Y . Intestinal digestibility of crude protein and dry matters with ruminant feedstuffs using the mobile nylon bag
Journal of Northeast Agricultural University. 2010,41(01):81-85.(in Chinese)
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[24] GAO W, CHEN A D, ZHANG B W, PING K, LIU C, JIE Z . Rumen degradability and post-ruminal digestion of dry matter, nitrogen and amino acids of three protein supplements
Asian-Australasian Journal of Animal Sciences, 2015,28(4):485-493.
DOI:10.5713/ajas.14.0572URLPMID:4341097 [本文引用: 1]
This study evaluated thein situruminal degradability, and subsequent small intestinal digestibility (SID) of dry matter, crude protein (CP), and amino acids (AA) of cottonseed meal (CSM), sunflower seed meal (SFSM) and distillers dried grains with solubles (DDGS) by using the modified three-stepin vitroprocedure. The ruminal degradability and subsequent SID of AA in rumen-undegradable protein (RUP-AA) varied among three protein supplements. The result show that the effective degradability of DM for SFSM, CSM, and DDGS was 60.8%, 56.4%, and 41.0% and their ruminal fermentable organic matter was 60.0%, 55.9%, and 39.9%, respectively. The ruminal degradable protein (RDP) content in CP for SFSM, CSM, and DDGS was 68.3%, 39.0%, and 32.9%, respectively, at the ruminal solid passage rate of 1.84%/h. The SFSM is a good source of RDP for rumen micro-organisms; however, the SID of RUP of SFSM was lower. The DDGS and CSM are good sources of RUP for lambs to digest in the small intestine to complement ruminal microbial AA of growing lambs. Individual RUP-AA from each protein source was selectively removed by the rumen micro-organisms, especially for Trp, Arg, His, and Lys (p<0.01). The SID of individual RUP-AA was different within specific RUP origin (p<0.01). Limiting amino acid was Leu for RUP of CSM and Lys for both RUP of SFSM and DDGS, respectively. Therefore, different protein supplements with specific limitations should be selected and combined carefully in growing lambs ration to optimize AA balance.

[25] OH Y K, PERK Y J, BAEK Y C, DO Y J, KIM D H, KWAK W S, CHOI H . In situ ruminal degradation and intestinal digestion of crude protein and amino acids of three major proteinaceous feeds for Hanwoo steers
Research Opinions in Animal and Veterinary Sciences, 2015,5(10):395-400.
URL [本文引用: 1]
Three Hanwoo steers (mean body weight 520卤20.2 kg), each fitted with a permanent ruminal cannula and a T-shaped duodenal cannula, were used to examine digestibility of crude protein (CP), rumen undegraded protein (RUP), and individual amino acids (AA) of three proteinaceous feeds (cottonseed meal, CSM; perilla meal, PRM; rapeseed meal, RSM), by using in situ bag and in situ mobile bag technique...

[26] 冷静, 张颖, 朱仁俊, 杨舒黎, 苟潇, 毛华明 . 云南黄牛对6种牧草瘤胃降解规律的研究
中国农学通报, 2011,27(01):398-402.
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LENG J, ZHANG Y, ZHU R J, YANG S L, GOU X, MAO H M . Study on rumen degradabilities of six forages in Yunnan yellow cattle
Chinese Agricultural Science Bulletin. 2011,27(01):398-402. (in Chinese)
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[27] CHALUPA W, SNIFFEN C J . Protein and amino acid nutrition of lactating dairy cattle-today and tomorrow
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[28] 岳群, 杨红建, 谢春元, 么学博, 王加启 . 应用移动尼龙袋法和三步法评定反刍家畜常用饲料的蛋白质小肠消化率
中国农业大学学报, 2007(6):62-66.
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YUE Q, YANG H J, XIE C Y, ME X B, WANG J Q . Estimation of protein intestinal digestibility of ruminant feedstuffs with mobile nylon bag technique and three-step in vitro procedure
.Journal of China Agricultural University, 2007(6):62-66. (in Chinese)
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[29] 李志静, 眭丹, 周玉香 . 不同蛋白水平对舍饲滩羊消化代谢及血液生化指标的影响
中国畜牧杂志, 2014,50(17):39-43.
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LI Z J, XU D, ZHOU Y X . Effect of dietary protein level on nutrient digestion metabolism and serum biochemical indexes in tan sheep
Chinese Journal of Animal Science. 2014,50(17):39-43. (in Chinese)
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[30] 孔祥浩, 郭金双, 朱晓萍, 贾志海, 岳春旺, 靳玲品, 李秀花, 秦艳红 . 不同NDF水平肉羊饲粮养分表观消化率研究
动物营养学报, 2010,22(1):70-74.
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KONG X H, GUO J S, ZHU X P, JIA Z H, YUE C W, JIN L P, LI X H, QIN Y H . Study on apparent nutrients digestibility of mutton sheep diets with different neutral detergent fiber levels
Chinese Journal of Animal Nutrition, 2010,22(1):70-74. (in Chinese).
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[31] HAIG P A, MUTSVANGWA T, SPRATT R, MCBRIDE B W . Effects of dietary protein solubility on nitrogen losses from lactating dairy cows and comparison with predictions from the Cornell Net Carbohydrate and Protein System
Journal of Dairy Science, 2002,85(5):1208-1217.
DOI:10.3168/jds.S0022-0302(02)74184-2URLPMID:12086057Magsci [本文引用: 1]
This experiment determined the effects of dietary protein solubility on amount, form, and route of nitrogen loss in lactating Holstein dairy cows, and the ability of the Cornell Net Carbohydrate and Protein System (CNCPS) to accurately predict rumen microbial yield, serum urea N (SUN), milk urea N (MUN), and fecal N. Eighteen multiparous Holstein cows were assigned randomly to one of three dietary treatments that were similar in crude protein (17.7%) content but differed in their content of soluble intake protein (SIP). Dietary contents of SIP, as % of total CP were 30, 36, and 48%. The experimental period was 21 d, and total N balance collections were done during the last 5 d. As dietary content of SIP increased, excretion of urinary N increased quadratically, and it was the primary route of N excretion. Urinary excretion of purine derivatives (PD) responded quadratically as dietary SIP content increased. The CNCPS predicted a quadratic decrease in total metabolizable protein (MP) supply. No effect of dietary content of SIP was detected on MUN and SUN. The CNCPS predicted a quadratic decrease in SUN and MUN as dietary SIP increased. Results from this study indicated that changing the dietary content of SIP altered routes of N excretion in dairy cows, but had no effect on total N balance. The CNCPS did not adequately predict changes in SUN and MUN for cows fed diets varying in SIP.

[32] HRISTOV A N, ETTER R P, ROPP J K, GRANDEEN K L . Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows
Journal of Animal Science, 2004,82(11):3219-3229.
DOI:10.2527/2004.82113219xURLPMID:15542468 [本文引用: 1]
Abstract The objectives of this experiment were to investigate the effects of two ruminally degradable protein (RDP) levels in diets containing similar ruminally undegradable protein (RUP) and metabolizable protein (MP) concentrations on ruminal fermentation, digestibility, and transfer of ruminal ammonia N into milk protein in dairy cows. Four ruminally and duodenally cannulated Holstein cows were allocated to two dietary treatments in a crossover design. The diets (adequate RDP [ARDP] and high RDP [HRDP]), had similar concentrations of RUP and MP, but differed in CP/RDP content. Ruminal ammonia was labeled with 15N and secretion of tracer in milk protein was determined for a period of 120 h. Ammonia concentration in the rumen tended to be greater (P = 0.06) with HRDP than with ARDP. Microbial N flow to the duodenum, ruminal digestibility of dietary nutrients, DMI, milk yield, fat content, and protein content and yield were not statistically different between diets. There was a tendency (P = 0.07) for increased urinary N excretion, and blood plasma and milk urea N concentrations were greater (P = 0.002 and P = 0.01, respectively) with HRDP compared with ARDP. Milk N efficiency was decreased (P = 0.01) by the HRDP diet. The cumulative secretion of ammonia 15N into milk protein, as a proportion of 15N dosed intraruminally, was greater (P = 0.003) with ARDP than with HRDP. The proportions of bacterial protein originating from ammonia N and milk protein originating from bacterial or ammonia N averaged 43, 61, and 26% and were not affected by diet. This experiment indicated that excess RDP in the diet of lactating dairy cows could not be efficiently utilized for microbial protein synthesis and was largely lost through urinary N excretion. At a similar MP supply, increased CP or RDP concentration of the diet would result in decreased efficiency of conversion of dietary N into milk protein and less efficient use of ruminal ammonia N for milk protein syntheses.

[33] PAENGKOUM P, LIANG J B, JELAN Z A, BASERY M . Effects of ruminally undegradable protein levels on nitrogen and phosphorus balance and their excretion in saanen goats fed oil palm fronds
Songklanakarin Journal of Science and Technology, 2004,26(1):15-22.
[本文引用: 1]