侯玉潔, 徐 俊, 郭小澤, 鄒新建, 曾柳根, 姚 毅, 侯小輝, 許亮清*
(1.南昌市農(nóng)業(yè)科學(xué)院,江西南昌330008;2.江西省農(nóng)業(yè)科學(xué)院農(nóng)產(chǎn)品質(zhì)量安全與標(biāo)準(zhǔn)研究所,江西南昌330200;3.江西省農(nóng)業(yè)科學(xué)院畜牧獸醫(yī)研究所,江西南昌330200;4.新疆阿勒泰市畜牧獸醫(yī)站,新疆阿勒泰836500)
不同牧草來(lái)源日糧對(duì)奶牛瘤胃發(fā)酵和微生物蛋白合成的影響
侯玉潔1, 徐 俊2*, 郭小澤3, 鄒新建1, 曾柳根1, 姚 毅1, 侯小輝4, 許亮清1*
(1.南昌市農(nóng)業(yè)科學(xué)院,江西南昌330008;2.江西省農(nóng)業(yè)科學(xué)院農(nóng)產(chǎn)品質(zhì)量安全與標(biāo)準(zhǔn)研究所,江西南昌330200;3.江西省農(nóng)業(yè)科學(xué)院畜牧獸醫(yī)研究所,江西南昌330200;4.新疆阿勒泰市畜牧獸醫(yī)站,新疆阿勒泰836500)
試驗(yàn)旨在研究不同牧草來(lái)源日糧對(duì)奶牛瘤胃發(fā)酵和微生物蛋白合成的影響。選用8頭體重為(632±12)kg泌乳中期奶牛(135±16 DIM),隨機(jī)分為4組,采用4×4重復(fù)拉丁方設(shè)計(jì),共4期,每期21 d,其中14 d適應(yīng)期,7 d采樣期。四組日糧均以玉米青貯為基礎(chǔ),粗飼料分別由苜蓿草、燕麥草、羊草和稻草組成,日糧等能等氮且中性洗滌纖維(NDF)和非纖維性碳水化合物(NFC)含量相同。結(jié)果顯示:(1)四組日糧中奶牛干物質(zhì)采食量(DMI)差異不顯著(P>0.05),瘤胃液pH、NH3-N、總揮發(fā)性脂肪酸(TVFA)和支鏈揮發(fā)性脂肪酸濃度均無(wú)顯著差異(P>0.05),稻草組乙酸含量偏低,丙酸含量偏高,但與其他三組并無(wú)顯著差異(P>0.05)。(2)稻草組奶牛每日尿排泄量有增加的趨勢(shì)(P=0.08),牧草來(lái)源對(duì)每日尿酸排泄量無(wú)顯著影響(P=0.87),但稻草組中尿囊素顯著低于苜蓿草、燕麥草和羊草組(P=0.01),造成總嘌呤衍生物(PD)含量顯著降低(P=0.01),稻草組微生物蛋白(MCP)產(chǎn)量比苜蓿草組降低124 g/d。綜上可知,在日糧NDF和NFC含量相同的條件下,不同牧草來(lái)源日糧對(duì)奶牛瘤胃發(fā)酵無(wú)顯著影響,且苜蓿草、燕麥草和稻草組微生物蛋白合成無(wú)顯著差異。
粗飼料;瘤胃發(fā)酵;微生物蛋白合成;奶牛
日糧纖維對(duì)于維持奶牛瘤胃健康和微生物氮利用效率至關(guān)重要,牧草是奶牛纖維的主要來(lái)源,尤其是青貯玉米,豆科牧草和禾本科干草(Eastridge等,2009),纖維在瘤胃微生物作用下降解為揮發(fā)性脂肪酸供能,促進(jìn)瘤胃微生物對(duì)日糧中氮的利用,可減少氮排放對(duì)環(huán)境造成的污染。
不同牧草蛋白、纖維和非纖維性碳水化合物(NFC)含量及消化率各不相同,它們會(huì)影響奶牛瘤胃發(fā)酵和微生物蛋白(MCP)合成(Lascano等,2010;Ramos等,2009),因此,通過(guò)改變?nèi)占Z組成提高瘤胃微生物對(duì)飼料降解率和生產(chǎn)性能的研究具有重要意義(Jones等,2009)。日糧中不同牧草來(lái)源和纖維水平對(duì)瘤胃發(fā)酵和微生物氮代謝至關(guān)重要(Weiss等,2009;Nousiainen等,2009),前人研究了日糧精粗比 (Lechartier和Peyraud,2010;Santra和Karim,2009),NDF水平 (Qiu等,2003)和牧草間替代 (Zhu等,2013;Official Methods of Analysis,1980)對(duì)奶牛瘤胃發(fā)酵、營(yíng)養(yǎng)物質(zhì)消化和泌乳性能的影響,但很少有研究不同牧草來(lái)源日糧中蛋白質(zhì)、能量和纖維等營(yíng)養(yǎng)組分對(duì)奶牛瘤胃發(fā)酵和MCP合成的影響。
因此,本研究選用我國(guó)牧場(chǎng)常用的四種牧草(苜蓿草、燕麥草、羊草和稻草)為粗飼料來(lái)源,以玉米青貯為基礎(chǔ)配制了四組等能等氮且NDF和NFC含量相同的日糧,研究不同牧草來(lái)源日糧對(duì)泌乳奶牛瘤胃發(fā)酵和MCP合成的影響。
1.1 試驗(yàn)動(dòng)物、日糧及飼養(yǎng)管理 選用8頭體重為(632±12)kg,泌乳天數(shù)為(135±16)d的泌乳中期荷斯坦奶牛。粗飼料以玉米青貯為基礎(chǔ),另一粗飼料分別來(lái)源于苜蓿草、燕麥草、羊草和稻草,牧草均由鍘草機(jī)鍘成3~5 cm,采用全混合日糧(TMR)方式進(jìn)行飼喂。精料主要為玉米、豆粕、棉籽粕、玉米干酒糟和預(yù)混料等,配制四組等能等氮且NDF和NFC含量相同的日糧。奶牛日喂3次 (06∶00,14∶30,22∶30),日擠奶3次(07∶00,15∶00,23∶00),單欄栓系式飼養(yǎng),采食后供以充足飲水,日糧組成及營(yíng)養(yǎng)成分如表1所示。
1.2 試驗(yàn)設(shè)計(jì) 8頭奶牛隨機(jī)分為四組,采用4× 4重復(fù)拉丁方設(shè)計(jì),進(jìn)行4期動(dòng)物試驗(yàn),每期21 d,前14 d預(yù)飼期,后7 d采樣期,準(zhǔn)確記錄每天干物質(zhì)采食量(DMI)。
1.3 樣品采集與測(cè)定
1.3.1 飼料及剩料樣品采集與分析 每期試驗(yàn)第15~17天采集TMR飼料樣和剩料樣各1 kg于-20℃保存,3 d采樣結(jié)束后,解凍并混合均勻,制備分析樣品。將樣品放入65℃烘箱中烘48 h,測(cè)定初水分,然后過(guò)40目篩,測(cè)定樣品粗蛋白質(zhì)(CP),粗脂肪(EE),有機(jī)物(OM),NDF和酸性洗滌纖維 (ADF)含量 (Van Soest等,1991),NFC= 100-(CP%+NDF%+EE%+Ash%)。飼料中鈣(Ca)和磷(P)采用電感耦合合等離子體原子發(fā)射光譜法測(cè)定(Official Methods of Analysis,1980)。
表1 TMR日糧組成及營(yíng)養(yǎng)成分
1.3.2 尿樣采集和嘌呤衍生物的測(cè)定 每期試驗(yàn)第15~17天通過(guò)點(diǎn)尿法采集晨飼后6 h和12 h尿樣100 mL,按1∶4的比例加入0.036 mol H2SO4,立即放入-20℃冷凍保存。每期采樣結(jié)束后,將每頭奶牛的尿液混合均勻,移取40 mL尿液并稀釋至200 mL制成次級(jí)尿樣,采用比色法測(cè)定尿中尿囊素和尿酸含量(Chen和Gomes,1995),肌酸苷含量利用試劑盒測(cè)定(BioVisione,K625-100)。
1.3.3 微生物蛋白產(chǎn)量的計(jì)算 本文根據(jù)尿中嘌呤衍生物(PD)排泄量估測(cè)MCP產(chǎn)量,其推算關(guān)系為:
式中:X為尿中PD數(shù)量,mmol/d;0.85表示牛腸道吸收的嘌呤轉(zhuǎn)化為尿中 PD的回收率;0.385表示吸收的嘌呤經(jīng)尿中排出的比率;BW0.75是奶牛代謝體重;70代表每mmol嘌呤中的氮含量,mg/mmol;0.83代表微生物嘌呤的小腸吸收率;0.116代表瘤胃微生物總氮中的嘌呤氮比例。
1.3.4 瘤胃液樣品采集及分析 每期試驗(yàn)的第19~20天采集瘤胃液樣品,通過(guò)口腔采集法采集晨飼后4 h瘤胃液150 mL(之前的唾液舍棄)。四層紗布過(guò)濾后立即測(cè)定pH;同時(shí)取過(guò)濾后的瘤胃液8 mL,加入2 mL新配制的25%偏磷酸,封蓋、倒置搖勻,11000 g離心20 min,上清液通過(guò)高效液相色譜法測(cè)定揮發(fā)性脂肪酸(VFA)濃度(Samue等,1997);另取2 mL濾液,加入0.5 moL HCl用于NH3-N含量的測(cè)定(Chaney和Marbach,1962)。
1.4 統(tǒng)計(jì)分析 數(shù)據(jù)采用Excel 2007進(jìn)行整理,結(jié)果采用SAS統(tǒng)計(jì)軟件的PDIFF模塊進(jìn)行方差分析和顯著性檢驗(yàn),以P<0.05作為差異顯著性判斷標(biāo)準(zhǔn)。
2.1 不同牧草來(lái)源日糧對(duì)瘤胃發(fā)酵的影響 由表2可知,四處理組中奶牛DMI分別為19.20、18.95、18.83和18.98 kg/d,各組間無(wú)顯著差異(P>0.05)。四組日糧中瘤胃液pH、NH3-N、TVFA和支鏈揮發(fā)性脂肪酸濃度也無(wú)顯著差異(P>0.05),雖然稻草組乙酸含量偏低,丙酸含量偏高,但與其他三組并無(wú)顯著差異(P>0.05),且從乙/丙比可知,四組日糧均為乙酸型發(fā)酵。
2.2 不同牧草來(lái)源日糧對(duì)微生物蛋白合成的影響 尿中PD和MCP估測(cè)量如表3所示,稻草組奶牛每日尿排泄量有增加的趨勢(shì)(P=0.08),牧草來(lái)源對(duì)每日尿酸排泄量無(wú)顯著影響(P=0.87),但稻草組中尿囊素顯著低于苜蓿、燕麥草和羊草組(P=0.01),造成總PD含量顯著降低(P=0.01),稻草組MCP產(chǎn)量比苜蓿組降低124 g/d。
3.1 不同牧草來(lái)源日糧對(duì)瘤胃發(fā)酵的影響 日糧中 NDF含量是限制奶牛 DMI的關(guān)鍵因素(Adin等,2009),當(dāng)粗飼料為NDF主要來(lái)源時(shí),DMI和NDF呈顯著的負(fù)相關(guān) (Ranathunga等,2010)。未鍘短牧草會(huì)影響DMI,但鍘短和粉碎過(guò)的牧草對(duì)奶牛的DMI無(wú)影響(Rode等,1985)。本研究中四組處理的DMI差異不顯著,這可能是因?yàn)樵撛囼?yàn)?zāi)敛菥彦幎虨?~5 cm長(zhǎng)且日糧中NDF含量相似。
表2 牧草來(lái)源對(duì)奶牛采食量和瘤胃發(fā)酵的影響
表3 牧草來(lái)源對(duì)尿排泄量、尿中嘌呤衍生物排泄量和微生物蛋白產(chǎn)量的影響
日糧纖維對(duì)瘤胃發(fā)酵至關(guān)重要,它們可以調(diào)控瘤胃 pH促進(jìn)瘤胃內(nèi)環(huán)境的穩(wěn)態(tài) (Haddad和Grant,2000),NRC建議日糧NDF中75%應(yīng)由粗飼料提供。本試驗(yàn)中NDF和NFC含量相近是造成瘤胃pH和TVFA含量無(wú)差異的重要原因,該結(jié)果與Eastridge等(2009)結(jié)果一致,粗飼料來(lái)源并不影響瘤胃發(fā)酵,而NDF和淀粉含量相近是造成乙酸和丙酸無(wú)差異的重要原因(Owens等,2009)。日糧中蛋白的降解是支鏈脂肪酸的主要來(lái)源,該試驗(yàn)中各處理組蛋白水平相似,使得瘤胃中支鏈脂肪酸未出現(xiàn)顯著差異(Berthiaume等,2010)。
3.2 不同牧草來(lái)源日糧對(duì)微生物蛋白合成的影響 MCP可為奶牛提供蛋白需要量的 40%~60%,MCP合成受日糧碳水化合物和蛋白含量的影響,日糧中能氮同步釋放有利于促進(jìn)瘤胃中MCP的合成(Moscardini等,1998)。稻草組小腸的MCP含量低于其他三組的原因可能是能量不夠引起的,盡管稻草組中NFC含量與其他三組類似。本試驗(yàn)稻草組中尿排放量及尿素氮含量均高于其他三組,降低尿氮排放量和尿素氮水平可以減少氮損失,提高NH3-N利用率,進(jìn)而促進(jìn)瘤胃MCP的合成 (Zhu等,2013),因此造成稻草組MCP合成量顯著低于其他牧草組。然而,大量研究發(fā)現(xiàn),奶牛瘤胃的日平均MCP合成量為1656 g,故稻草組MCP合成量(1699 g/d)可以滿足奶牛乳蛋白合成的需要(Clark等,1992)。盡管豆科牧草CP和NFC含量高于禾本科牧草,它們可以提供更多能量和可降解蛋白以合成MCP,但本試驗(yàn)各組日糧中蛋白、纖維和能量水平相同,這也許是造成MCP合成量差異不顯著的主要原因。
本研究結(jié)果表明,在日糧NDF和NFC含量相同的條件下,不同牧草來(lái)源日糧對(duì)奶牛瘤胃發(fā)酵無(wú)顯著影響,且苜蓿草、燕麥草和稻草組微生物蛋白合成也無(wú)顯著差異。
[1]Association of Official Analytical Chemists.Official Methods of Analysis[M]. Washington.DC:1980.
[2]Adin G.Solomon R.Nikbachat M.roughage-neutral detergent fiber content on intake behavior,rumination.and milk production[J].Journal of Dairy Science,2009,92(7):3364~3373.
[3]Berthiaume R.Benchaar C.Chaves A.et al.Effects of nonstructural carbohydrate concentration in alfalfa on fermentation and microbial protein synthesis in continuous culture[J].Journal of Dairy Science,2010,93(2):693~700.
[4]Chen X B.Gomes M.Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivatives-an overview of the technical details[M].International Feed Resources Unit:1995.
[5]Chaney AL.Marbach EP.Modified reagents for determination of urea and ammonia[J].Clinical Chemistry,1962,8:130~132.
[6]Clark J.Klusmeyer T.Cameron M.Microbial protein synthesis and flows of nitrogen fractions to the duodenum of dairy cows[J].Journal of Dairy Science,1992,75(8):2304~2323.
[7]Eastridge M,Bucci P,Ribeiro C.Feeding equivalent concentrations of forage neutral detergent fiber from alfalfa hay,grass hay,wheat straw.and whole cottonseed in corn silage based diets to lactating cows[J].Animal Feed Science and Technology,2009,150(1):86~94.
[8]Eastridge M.Bucci P.Ribeiro C.Feeding equivalent concentrations of forage neutral detergent fiber from alfalfa hay.grass hay.wheat straw.and whole cottonseed in corn silage based diets to lactating cows[J].Animal Feed Science and Technology,2009,150(1):86~94.
[9]Haddad S.Grant R.Influence of nonfiber carbohydrate concentration on forage fiber digestion in vitro [J].Animal Feed Science and Technology,2000,86(1):107~115.
[10]Jones R T.Robeson M S.Lauber C L.et alA comprehensive survey of soil acidobacterial diversity using pyrosequencing and clone library analyses[J].The ISME Journal,2009,3(4):442~453.
[11]Lascano G.Zanton G.Heinrichs A.et al.Technical note:A noninvasive urine collection device for female cattle:Modification of the urine cup collection method[J].Journal of Dairy Science,2010,93(6):2691~2694.
[12]Lechartier C.Peyraud J L.The effects of forage proportion and rapidly degradable dry matter from concentrate on ruminal digestion in dairy cows fed corn silage-based diets with fixed neutral detergent fiber and starch contents [J].Journal of Dairy Science,2010,93(2):666~681.
[13]Moscardini S.Wright T.Luimes P.et al.Effects of rumen-undegradable protein and feed intake on purine derivative and urea nitrogen:comparison with predictions from the Cornell Net Carbohydrate and Protein System[J]. Journal of Dairy Science,1998,81(9):2421~2429.
[14]Nousiainen J.Rinne M.Huhtanen P.A meta-analysis of feed digestion in dairy cows.1.The effects of forage and concentrate factors on total diet digestibility[J].Journal of Dairy Science,2009,92(10):5019.
[15]Owens D.McGee M.Boland T.et al.Rumen fermentation.microbial protein synthesis.and nutrient flow to the omasum in cattle offered corn silage. grass silage.or whole-crop wheat[J].Journal of Animal Science,2009,87(2):658~668.
[16]Qiu X.Eastridge M.Wang Z.Effects of corn silage hybrid and dietary concentration of forage NDF on digestibility and performance by dairy cows[J]. Journal of Dairy Science,2003,86(11):3667~3674.
[17]Ramos S.Tejido M.Martínez M.et al.Microbial protein synthesis.ruminal digestion.microbial populations.and nitrogen balance in sheep fed diets varying in forage-to-concentrate ratio and type of forage[J].Journal of Animal Science,2009,87(9):2924~2934.
[18]Rode L M.Weakley D C.Satter L D.Effect of forage amount and particle size in diets of lactating dairy cows on site of digestion and microbial protein synthesis[J].Canadian Journal of Animal Science,1985,65:101~111.
[19]Ranathunga S.Kalscheur K.Hippen A.et al.Replacement of starch from corn with nonforage fiber from distillers grains and soyhulls in diets of lactating dairy cows[J].Journal of Dairy Science,2010,9(3):1086~1097.
[20]Santra A.Karim S.Effect of dietary roughage and concentrate ratio on nutrient utilization and performance of ruminant animals[J].Animal Nutrition and Feed Technology,2009,9(2):113~135.
[21]Samuel M.Sagathewan S.Thomas J.et al.An HPLC method for estimation of volatile fatty acids of ruminal fluid[J].Indian Journal of Animal Sciences,1997,69:805~807.
[22]Van Soest.Van P J.Robertson J B.et al.Methods for dietary fiber.neutral detergent fiber and nonstarch polysaccharides in relation to animal nutrition[J]. Journal of Dairy Science,1991,74:3583~3597.
[23]Weiss W.St-Pierre N.Willett L.Varying type of forage.concentration of metabolizable protein.and source of carbohydrate affects nutrient digestibility and production by dairy cows[J].Journal of Dairy Science,2009,92(11):5595~5606.
[24]Zhu W.Fu Y.Wang B.et al.Effects of dietary forage sources on rumen microbial protein synthesis and milk performance in early lactating dairy cows [J].Journal of Dairy Science,2013,96(3):1727~1734.
A total of 8 Holstein dairy cows with average weight(632±12)kg and middle lactation[(135±16)DIM]were selected,and a replicated 4×4 latin square design was used to evaluate the effects of forage sources on rumen fermentation characteristics and microbial protein(MCP)synthesis.Alfalfa hay(AH),oat hay(OH),leymus chinensis(LC)and rice straw(RS)were primary sources of fiber,diets were isonitrogenous and isocaloric,and based on corn silages,total mixed rations with equivalent neutral detergent fiber (NDF)and nonfiber carbohydrate (NFC).The results showed that:(1)The dry matter intake(DMI),the concentrations of pH,ammonia nitrogen,TVFA and branched volatile fatty acids were not affected by the source of dietary forages (P>0.05).The acetate content of rice straw was much lower,and the content of propionate was much higher than other groups.(2)The urine excretion of cows had the trend of increasing in rice straw group(P=0.08),the source of dietary forages had no effect on uric acid excretion,but allantoin output of rice straw was lower than alfalfa hay,oat hay and leymus chinensis(P=0.01),so the total purine derivatives(PD)excretion significantly decreased.Microbial protein of rice straw lower than alfalfa hay by 124 g/d.According to the results,the cows were fed with AH,OH,LC,and RS with equivalent NDF and NFC contents had no unfavourable effect on ruminal fermentation and MCP synthesis.
forage sources;rumen fermentation;microbial protein synthesis;dairy cows
10.15906/j.cnki.cn11-2975/s.20170806
S816.5
A
1004-3314(2017)08-0021-04
國(guó)家自然基金“SARA影響錦江黃牛胃腸道微生物和宿主代謝的關(guān)聯(lián)研究”(31560647)
*通訊作者