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        飼糧氮水平對牦牛尿嘌呤衍生物排出量與瘤胃微生物氮產(chǎn)量的影響

        2017-11-17 01:16:23王惟惟王傳洋郝力壯仲崇亮周建偉龍瑞軍
        動物營養(yǎng)學(xué)報 2017年11期
        關(guān)鍵詞:產(chǎn)量水平

        王惟惟 王傳洋 郝力壯 劉 浩 仲崇亮 周建偉 龍瑞軍*

        (1.蘭州大學(xué)草地農(nóng)業(yè)科技學(xué)院,蘭州 730000;2.青海省都蘭縣畜牧獸醫(yī)工作站,都蘭 816199;3.青海大學(xué)畜牧獸醫(yī)科學(xué)院,西寧 810016;4.蘭州大學(xué)生命科學(xué)學(xué)院,蘭州 730000)

        飼糧氮水平對牦牛尿嘌呤衍生物排出量與瘤胃微生物氮產(chǎn)量的影響

        王惟惟1王傳洋2郝力壯3劉 浩1仲崇亮1周建偉4龍瑞軍4*

        (1.蘭州大學(xué)草地農(nóng)業(yè)科技學(xué)院,蘭州 730000;2.青海省都蘭縣畜牧獸醫(yī)工作站,都蘭 816199;3.青海大學(xué)畜牧獸醫(yī)科學(xué)院,西寧 810016;4.蘭州大學(xué)生命科學(xué)學(xué)院,蘭州 730000)

        本試驗旨在探討牦牛尿中嘌呤衍生物(PD)排出量對飼糧氮水平的響應(yīng)規(guī)律,并基于此估測了瘤胃微生物氮(MN)產(chǎn)量,以期為高寒牧區(qū)牦牛的科學(xué)飼養(yǎng)提供參考。選取4頭體重[(192±12) kg]相近、年齡(3歲)相同的去勢公牦牛,采用4×4拉丁方試驗設(shè)計將牦牛分為4組,各組飼糧氮水平分別是1.03%、1.95%、2.85%和3.76%,每組1頭;試驗分為4期,每期21 d,包含15 d的預(yù)試期和6 d的正試期。結(jié)果表明,牦牛尿中PD主要由尿囊素和尿酸組成,尿囊素/PD和尿酸/PD分別為0.69~0.76、0.23~0.30,黃嘌呤與次黃嘌呤的含量極少。當(dāng)飼糧氮水平升高時,尿中PD、尿囊素、尿酸以及馬尿酸排出量均線性增加(P<0.05),而尿酸/PD和嘌呤氮指數(shù)(PNI)均線性降低(P<0.05)。瘤胃細(xì)菌嘌呤堿基(RNA當(dāng)量)含量、瘤胃細(xì)菌氮含量以及瘤胃MN產(chǎn)量都隨著飼糧氮水平升高而線性增加(P<0.05),但飼糧氮用于合成MN的效率[即瘤胃MN/食入氮(NI)]卻線性降低(P<0.05)?;谀蛑蠵D排出量(mmol/d)和瘤胃MN產(chǎn)量(g/d)與NI(g/d)之間良好的線性關(guān)系,構(gòu)建了如下數(shù)學(xué)模型:PD=0.58NI+18.28,MN=0.18NI+22.18。綜合得出,當(dāng)牦牛飼糧氮水平為2.85%時,牦牛瘤胃MN產(chǎn)量最大,為42.60 g/d,而PNI以及飼糧氮用于合成MN的效率卻在低氮(1.03%)條件下達到最高,這一結(jié)果揭示了牦牛對低氮飼糧中氮素營養(yǎng)高效利用的特點,解釋了牦牛對青藏高原飼料營養(yǎng)匱乏的適應(yīng)性的營養(yǎng)機理。

        牦牛;飼糧氮水平;尿中嘌呤衍生物;瘤胃微生物氮產(chǎn)量

        與單胃動物相比,反芻動物最明顯的特點是擁有一個體積龐大的瘤胃,其中棲息著數(shù)量驚人的微生物。瘤胃微生物不但能夠分泌大量的消化酶來幫助宿主動物降解纖維性飼料,而且能夠為其提供機體營養(yǎng)代謝所需的各種氨基酸資源。據(jù)報道,反芻動物小腸所吸收的氨基酸有1/2以上都來自瘤胃微生物[1],特別是在營養(yǎng)脅迫條件下,瘤胃微生物幾乎就是宿主唯一的可消化蛋白質(zhì)源[2]。鑒于此,瘤胃微生物氮(MN)的準(zhǔn)確定量對評價反芻動物氮素的利用效率具有重要意義。

        牦牛是青藏高原的特有畜種,其對高海拔、寒冷、缺氧、強紫外輻射和牧草生長期短的惡劣環(huán)境具有極強的適應(yīng)能力[10]。經(jīng)過成百上千年的自然和人工選擇,牦牛體內(nèi)可能已經(jīng)形成了一系列特殊的營養(yǎng)代謝機制來抵抗冷季飼草料供應(yīng)不足的威脅,從而保證了其種群的正常繁衍生息[11-12]。研究表明,牦牛的氮維持需要量較低[0.40~0.53 g/(kg W0.75·d)][13-14];牦牛飼糧氮的利用效率較黑白花奶牛高[15];在氮脅迫條件下,牦牛肝臟合成的尿素有87%可被循環(huán)進入消化道,為瘤胃微生物合成微生物蛋白質(zhì)提供氮源[16]。上述這些研究結(jié)果都從一定程度上反映了牦牛微生物蛋白質(zhì)合成效率可能較其他低海拔牛種要高。因此,本試驗試圖通過研究飼糧氮水平對牦牛尿PD排出規(guī)律的影響,并基于此來估測瘤胃MN產(chǎn)量,從而為揭示牦牛特殊的氮素營養(yǎng)代謝機制提供理論依據(jù)。

        1 材料與方法

        1.1試驗地點和時間

        野外飼養(yǎng)試驗和樣品采集工作于2013年11月至2014年1月在甘肅省天祝藏族自治縣烏鞘嶺牦牛試驗站(北緯37°12.479′,東經(jīng)102°51.695′,海拔3 154 m)完成;樣品室內(nèi)分析于2014年2月至5月在蘭州大學(xué)青藏高原生態(tài)系統(tǒng)管理國際中心進行。

        1.2試驗動物和飼糧

        選取4頭體重[(192±12) kg]相近、年齡(3歲)相同的健康去勢公牦牛,試驗開始前對其作驅(qū)蟲處理,并置于代謝籠內(nèi)進行30 d的適應(yīng)期,使其熟悉飼養(yǎng)條件、試驗人員和周圍環(huán)境。飼糧的精粗比為50∶50,其中粗料為青稞秸稈,精料為4種代謝能和中性洗滌纖維基本相同而氮水平不同的顆粒料。4種飼糧氮水平分別為1.03%、1.95%、2.85%、3.76%(干物質(zhì)基礎(chǔ))。試驗飼糧組成及營養(yǎng)水平見表1。通過前期的預(yù)試驗確定牦牛的干物質(zhì)食量為3 kg/d,約為體重的1.5%,飼糧的能量水平為1.1倍維持需要量[生長牦牛能量維持需求為458 kJ/(kg W0.75·d)][17]。

        表1 試驗飼糧組成及營養(yǎng)水平(干物質(zhì)基礎(chǔ))

        續(xù)表1項目Items飼糧氮水平DietaryNlevel/%1.031.952.853.76粗灰分Ash6.226.526.827.12中性洗滌纖維NDF67.6165.7364.1162.36酸性洗滌纖維ADF25.6227.5329.2230.91

        1)預(yù)混料為每千克飼糧提供The premix provided the following per kg of diets:CuSO41 225 mg,ZnSO43 519 mg,F(xiàn)eSO44 080 mg,MnSO43 516.6 mg,KI 543.4 mg,Na2SeO382 mg,CoCl24.8 mg,莫能菌素 monensin 6 000 mg,VA 500 000 IU,VD3200 000 IU,VE 2 000 IU。

        2)代謝能根據(jù)《中國飼料成分及營養(yǎng)價值表(2013年第24版)》[18]計算,其余為實測值。ME was calculated according toTablesofFeedCompositionandNutritiveValuesinChina(2013,24th ed.)[18], while the others were measured values.

        1.3試驗設(shè)計與飼養(yǎng)管理

        本試驗采用4×4拉丁方試驗設(shè)計,整個試驗分為4期,每期21 d(包括15 d的預(yù)試期和6 d的正試期)。試驗牦牛于每天08:00和18:00各飼喂1次,每次干物質(zhì)飼喂量為1.5 kg,自由飲水,在每個正試期的第1天和最后1天空腹稱重。

        1.4樣品采集與處理

        每期正試期第1天的晨飼前,采用全收尿法連續(xù)收集尿液5 d,并記錄每天每頭牦牛的排尿量。將每天收集的尿樣混勻,按總尿量的10%取樣,用50%的H2SO4酸化,使pH<3.0,以利于固定尿中氮和避免微生物生長,并在-20 ℃的冰箱中保存。每期正試期最后1 d晨飼前以及飼喂后的2、4、6、8 h,利用口腔式胃管抽取瘤胃液,每次大約取樣100 mL,4層紗布過濾后裝入離心管,在-20 ℃的冰箱中保存。

        1.5測定方法及計算公式

        牦牛尿中PD(尿囊素、尿酸、黃嘌呤、次黃嘌呤)含量利用高效液相色譜儀(Agilent,LC-1200)測定,參考李曉鵬等[19]的方法。瘤胃微生物的提取參考Wickersham等[20]的方法,瘤胃細(xì)菌嘌呤堿基(RNA當(dāng)量)、瘤胃細(xì)菌嘌呤氮(purine nitrogen,PN)含量的測定參考Zinn等[21]的方法,瘤胃細(xì)菌氮(bacterial nitrogen,BN)含量和尿氮排出量利用凱氏定氮法測定[22]。

        牦牛瘤胃MN產(chǎn)量計算根據(jù)前人所建立[23]以及修正的模型[9]。牦牛小腸吸收嘌呤量(X,mmol/d)與尿中PD排出量(Y,mmol/d)的關(guān)系如下:

        Y=0.85X+0.134BW0.75。

        式中:BW0.75為代謝體重(kg)。

        牦牛瘤胃MN產(chǎn)量估測公式如下:

        MN(g/d)=(X×70)/[(PN∶BN)×0.83×1 000]。

        式中:X為小腸吸收嘌呤量(mmol/d);70指每毫摩爾嘌呤含70 mg氮;0.83指微生物核酸的消化率。

        嘌呤氮指數(shù)(PNI)=尿嘌呤氮排出量/

        尿氮排出量[24]。

        1.6數(shù)據(jù)處理與分析

        試驗數(shù)據(jù)利用SAS 9.2 PROC MIXED模塊進行多項式正交對比來檢驗其差異顯著性,其中飼糧氮水平為固定因子,試驗動物和試驗期為隨機因子;線性相關(guān)性分析及其模型關(guān)系圖制作采用R Studio 1.0.143軟件進行。

        2 結(jié)果與分析

        2.1尿中PD排出量及小腸吸收嘌呤量

        由表2可見,牦牛尿中PD主要由尿囊素和尿酸組成,黃嘌呤和次黃嘌呤含量都極少且不受飼糧氮水平影響(P>0.05)。隨著飼糧氮水平的升高,牦牛尿中尿囊素、尿酸和PD排出量以及小腸吸收嘌呤量均線性增加(P<0.05)。尿囊素/PD為0.69~0.76,尿酸/PD為0.23~0.30,尿囊素/PD隨著飼糧氮水平升高而線性增加(P<0.05),而尿酸/PD的變化趨勢與之相反。牦牛尿中馬尿酸排出量隨著飼糧氮水平的增加而線性升高(P<0.05),而PNI卻隨之線性降低(P<0.05),變化范圍為0.06~0.22,并且在飼糧氮水平為1.03%時達到最高值。

        表2 飼糧氮水平對牦牛尿中PD排出量及小腸吸收嘌呤量的影響

        2.2瘤胃細(xì)菌參數(shù)和MN產(chǎn)量

        由表3可見,牦牛瘤胃細(xì)菌中瘤胃細(xì)菌嘌呤堿基(RNA當(dāng)量)、瘤胃細(xì)菌PN、瘤胃BN含量以及瘤胃細(xì)菌PN/瘤胃BN都隨著飼糧氮水平的升高而線性增加(P<0.05),其中瘤胃細(xì)菌PN/瘤胃BN的變化范圍在0.12~0.20。瘤胃MN產(chǎn)量也隨著飼糧氮水平的升高而先增加后降低,當(dāng)飼糧氮水平在2.85%時,牦牛瘤胃MN產(chǎn)量最高,為42.60 g/d。隨著飼糧氮水平的升高,瘤胃MN/NI線性減小(P<0.05),這表明飼糧氮用于合成MN的效率逐漸降低。

        表3 飼糧氮水平對牦牛瘤胃細(xì)菌參數(shù)及微生物氮產(chǎn)量的影響

        由于飼糧食入氮(NI,g/d)與PD(mmol/d)、MN(g/d)均呈現(xiàn)較高的線性相關(guān)關(guān)系,通過線性回歸分析建立了它們之間的數(shù)學(xué)模型(圖1),模型如下:PD=0.58NI+18.28(R2=0.93),MN=0.18NI+22.18(R2=0.60)。

        圖1 尿中PD排出量(A)和瘤胃微生物氮產(chǎn)量(B)與食入氮的相關(guān)關(guān)系

        3 討 論

        3.1牦牛尿中PD排出量對飼糧氮水平的響應(yīng)規(guī)律

        反芻動物尿中PD主要源自瘤胃微生物核酸[25],而瘤胃MN產(chǎn)量隨飼糧氮水平升高而增加,從而導(dǎo)致尿中PD及其組分排出量的增加,這與Guo等[16]在牦牛和周建偉[26]在綿羊上的研究結(jié)果相一致。本試驗小腸吸收嘌呤量隨飼糧氮水平線性升高,這是因為氮采食量的升高促進了瘤胃中微生物核酸的合成代謝[27],當(dāng)微生物核酸降解為嘌呤時,小腸黏膜吸收的嘌呤會因此升高。

        反芻動物尿中PD由尿囊素、尿酸、黃嘌呤及次黃嘌呤構(gòu)成,尿囊素和尿酸所占比重較大[28],而黃嘌呤和次黃嘌呤所占比重較小[29-30]。本試驗結(jié)果顯示,牦牛尿囊素/PD和尿酸/PD分別為0.69~0.76和0.23~0.30,與Long等[13]和Wang等[31]在牦牛中報道的結(jié)果一致,與Chen[30]關(guān)于黃牛等的報道基本相近。隨著飼糧氮水平升高,尿囊素/PD線性上升,尿酸/PD線性下降,這與Long等[32]和王虎成[9]研究結(jié)果變化趨勢相同。研究結(jié)果顯示,牦牛尿中PD中黃嘌呤和次黃嘌呤很低或者幾乎沒有(含量<1%),與Chen[30]報道的黃牛的研究結(jié)果相近,但綿羊尿中PD中黃嘌呤與次黃嘌呤含量相對較高(為16.1%),這可能與動物體內(nèi)的黃嘌呤氧化酶活性有關(guān)。與綿羊相比,??苿游锏母闻K、血液、小腸黏膜細(xì)胞具有較高的黃嘌呤氧化酶活性,其體內(nèi)的黃嘌呤和次黃嘌呤很容易被氧化而形成尿酸[9,27]。

        3.2瘤胃細(xì)菌嘌呤堿基、BN含量,MN產(chǎn)量及PNI對飼糧氮水平的響應(yīng)規(guī)律

        本試驗中牦牛瘤胃細(xì)菌嘌呤堿基(RNA當(dāng)量)含量為5.42%~12.53%,平均值為8.97%,與韓興泰等[33]在牦牛上的研究結(jié)果(8.3%~11.4%,平均值為9.85%)相近,較Smith等[34]在奶牛及綿羊中研究結(jié)果(5.2%~6.8%,平均值為5.7%)高;BN含量(4.28%~6.21%)也與韓興泰等[33]研究的結(jié)果(4.64%~5.92%)相近,低于奶牛(5.76%~9.12%)[34]。周建偉[26]在藏羊?qū)Φ孛{迫適應(yīng)性的研究中也發(fā)現(xiàn),藏羊瘤胃微生物RNA含量(6.62%~8.17%)較細(xì)毛羊高,而BN含量(2.96%~3.18%)相對較低。因此,高海拔地區(qū)反芻動物(如藏羊、牦牛)瘤胃微生物具有高RNA和低氮素的特點,這可能是其長期適應(yīng)青藏高原飼草營養(yǎng)脅迫的結(jié)果。在早期的研究中,瘤胃微生物的瘤胃細(xì)菌PN/瘤胃BN被認(rèn)為比較穩(wěn)定,平均值為0.116[23]。但隨著研究地深入,發(fā)現(xiàn)該比值的變異較大,受到采食量、微生物群落組成、動物品種等因素的影響[35-37]。本試驗中瘤胃細(xì)菌PN/瘤胃BN在0.12~0.20波動,說明飼糧氮水平也影響該比值。

        隨著氮水平升高,瘤胃MN產(chǎn)量線性升高,表現(xiàn)趨勢與Sannes等[38]和Devant等[39]結(jié)果一致。在1.95%飼糧氮水平條件下,瘤胃MN產(chǎn)量為33.56 g/d,與Guo等[16]報道1.97%飼糧氮水平下瘤胃MN產(chǎn)量(31.1 g/d)相近。瘤胃MN/NI反映瘤胃微生物將飼糧氮轉(zhuǎn)化為MN的效率,本試驗中該比值在1.03%的低氮水平飼糧條件下達到最高(0.82),這表明在低氮水平飼糧條件下,飼糧氮轉(zhuǎn)化為瘤胃MN的效率較高;同時也證實了在氮素營養(yǎng)脅迫下,微生物蛋白質(zhì)是宿主動物最重要氨基酸來源。在3.76%的高氮水平飼糧條件下瘤胃MN/NI最低,為0.34,這是因為牦牛在采食高氮飼糧時,進入小腸的過瘤胃蛋白質(zhì)數(shù)量增加,宿主對微生物蛋白質(zhì)所提供的氨基酸的依賴性降低。

        PNI是快速評價飼糧氮轉(zhuǎn)化為MN效率的重要指標(biāo),PNI越高,表明瘤胃降解氮合成微生物蛋白質(zhì)的效率較高。本試驗PNI變化范圍在0.06~0.22,與Wang等[31]的報道范圍(0.07~0.15)相近。PNI隨著飼糧氮水平升高而降低,與Zhou等[40]在藏羊上的研究結(jié)果相同,但Wang等[31]卻發(fā)現(xiàn)PNI隨著干草采食量的增加而變大。低氮飼糧下較高的PNI表明,牦牛在氮素脅迫下,微生物能夠有效利用瘤胃可降解蛋白質(zhì),以彌補飼糧氮素匱乏的限制,從而向牦牛提供更多的氨基酸。

        3.3尿中PD排出量和瘤胃MN產(chǎn)量的估測模型

        反芻家畜小腸吸收嘌呤量和基于PD法的瘤胃MN產(chǎn)量估測模型(表4[5-9]、表5[41-44]),參數(shù)變異較大,尤其是不同物種之間。本試驗?zāi)蛑蠵D排出量與估測瘤胃MN產(chǎn)量表現(xiàn)出強線性相關(guān)(R2=0.71),這與表5中各研究所建立的估測模型

        結(jié)果相符。Reynal等[45]的研究發(fā)現(xiàn),采用15N作標(biāo)記物估測瘤胃MN產(chǎn)量較PD法具有更高的準(zhǔn)確性,但Ma等[43]也證明了2種方法之間存在較高相關(guān)性(R2=0.82),說明了PD法的可靠性。尿中PD估測瘤胃MN產(chǎn)量需要校正瘤胃微生物的PN∶BN。Perez等[46]報道,液相與固相微生物的PN∶BN不同,而固相微生物約占其總量的70%[47],因此在測定該比值時應(yīng)同時提取固相和液相微生物,并保持合適的比例。在本試驗中只考慮了液相微生物,因此所估測瘤胃MN產(chǎn)量并不是十分準(zhǔn)確。據(jù)報道,小腸吸收的氨基酸有11%來自原蟲[48],并且細(xì)菌的PN∶BN高于原蟲[49]。在分離瘤胃微生物的過程中,原蟲容易在離心時與飼料顆粒一起被沉淀,最后分離得到的瘤胃微生物主要是細(xì)菌而不包含原蟲[49-50]。因此,利用細(xì)菌中的PN∶BN來代替整個瘤胃微生物的比值,這會低估了瘤胃MN產(chǎn)量。

        表4 尿中PD排出量(mmol/d)與小腸吸收嘌呤量(X, mmol/d)的關(guān)系模型

        表5 尿中PD排出量(mmol/d)與瘤胃MN產(chǎn)量(g/d)的關(guān)系模型

        3.4飼糧氮水平對尿中馬尿酸排出量的影響

        苯甲酸和甘氨酸是合成馬尿酸的前體物質(zhì),苯甲酸主要由腸道細(xì)菌分解小腸下游飼糧多酚類物質(zhì)(瘤胃中較難降解)而產(chǎn)生,在肝臟中與甘氨酸共軛作用形成馬尿酸[51-53],并以此來防止苯甲酸中毒。在本試驗中,尿中馬尿酸排出量隨著飼糧氮水平的升高而增加,這與劉浩等[54]在藏羊上的研究結(jié)果一致。瘤胃中被降解的蛋白質(zhì)是腸道酚類化合物的主要來源[55],飼糧氮水平增加,增加了苯甲酸合成的主要前體物,促進了苯甲酸的產(chǎn)生[56],進而增加了馬尿酸的合成。

        4 結(jié) 論

        當(dāng)牦牛飼糧氮水平為2.85%時,牦牛瘤胃MN產(chǎn)量最大,為42.60 g/d,而PNI以及飼糧氮用于合成MN的效率卻在低氮(1.03%)條件下達到最高,這一結(jié)果揭示了牦牛對低氮飼糧中氮素營養(yǎng)高效利用的特點,解釋了牦牛對青藏高原飼料營養(yǎng)匱乏的適應(yīng)性的營養(yǎng)機理。

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        *Corresponding author, professor, E-mail: longrj@lzu.edu.cn

        EffectsofDietaryNitrogenLevelonUrinePurineDerivativesExcretionandMicrobialNitrogenProductioninYaks

        WANG Weiwei1WANG Chuanyang2HAO Lizhuang3LIU Hao1ZHONG Chongliang1ZHOU Jianwei4LONG Ruijun4*

        (1.CollegeofPastoralAgricultureScienceandTechnologyofLanzhouUniversity,Lanzhou730000,China; 2.AnimalHusbandryandVeterinaryStationofDulanCounty,Dulan816199,China; 3.CollegeofAnimalScienceandVeterinaryMedicineofQinghaiUniversity,Xining810016,China; 4.SchoolofLifeSciencesofLanzhouUniversity,Lanzhou730000,China)

        This experiment was conducted to explore the regularity of urine purine derivatives (PD) excretion respond to dietary nitrogen level, and based on this, ruminal microbial nitrogen (MN) production was estimated, thus provided references for appropriate feeding of yaks in cold farming area. Four 3-year-old castrated male yaks [body weight was (192±12) kg] were divided into 4 groups with 1 yak per group in a 4×4 Latin square design. Dietary nitrogen levels of different groups were 1.03%, 1.95%, 2.85% and 3.76%, respectively. The experiment consisted of 4 periods, each lasted for 21 d, allowing a 15-d pre-test period and a 6-d test period. The results showed that urine PD were mainly consist of allantoin and uric acid, allantoin/PD and uric acid/PD were 0.69 to 0.76 and 0.23 to 0.30, respectively, and negligible contents of xanthine and hypoxanthine were found. As dietary nitrogen level increasing, urine PD, allantoin, uric acid and hippuric acid extractions were increased linearly (P<0.05), however, uric acid/PD and purine nitrogen index (PNI) were linearly decreased (P<0.05). With the increase of dietary nitrogen level, ruminal bacterial purine bases (RNA equivalent) content, bacterial nitrogen (BN) content and MN production were linearly increased (P<0.05), and efficiency of dietary nitrogen converted into MN [ruminal MN/nitrogen intake (NI)] was linearly decreased (P<0.05). There were a strong relationship between urine PD extraction (mmol/d), ruminal MN (g/d) and NI (g/d), the following mathematical equations were established as follows: PD=0.58NI+18.28, MN=0.18NI+22.18. In summary, ruminal MN production is the highest (42.60 g/d) when dietary nitrogen level is 2.85%, whereas PNI and efficiency of NI converted into MN are the highest under the condition of low dietary nitrogen level (1.03%). The results indicate the great efficiency of nitrogen utilization when low nitrogen provision in yaks, and their adaptation nutrition mechanism to the deficiencies in intake of nutrient of yaks in Tibetan plateau.[ChineseJournalofAnimalNutrition,2017,29(11):3932-3941]

        yak; dietary nitrogen levels; urine purine derivatives; ruminal microbial nitrogen production

        10.3969/j.issn.1006-267x.2017.11.013

        S823

        A

        1006-267X(2017)11-3932-10

        2017-04-14

        國家自然科學(xué)基金(31672453);中國博士后科學(xué)基金(2016M600825);蘭州大學(xué)“中央高?;究蒲袠I(yè)務(wù)專項資金”(lzujbky-2015-bt08)

        王惟惟(1990—),男,貴州六盤水人,博士研究生,從事反芻動物營養(yǎng)研究。E-mail: wangww14@lzu.edu.cn

        *通信作者:龍瑞軍,教授,博士生導(dǎo)師,E-mail: longrj@lzu.edu.cn

        (責(zé)任編輯 王智航)

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