反刍动物小肠氨基酸调控

<正>反刍动物蛋白质营养研究,由传统的粗蛋白质或可消化蛋白质体系,转向降解和非降解蛋白质体系及小肠可消化蛋白质体系,迄今已将研究重点,转移到小肠氨基酸来源、数量、组成及蛋白质周转方面。反刍动物氨基酸需要是反刍动物小肠氨基酸调控的基础,是通过对饲料以及消化系统的调控,使进入小肠的氨基酸达到动物的生产需要。反刍动物小肠中吸收的氨基酸包括3个来源蛋白质的降解:①瘤胃微生物蛋白;②饲料非降解蛋白;③内源蛋白质。饲料非降解蛋白质和瘤胃微生物蛋白质在小肠内被消化吸收,微生物蛋白质是小肠氨基酸的主要来源,空肠回肠是氨基酸的主要吸收部位,因此瘤胃微生物蛋白质产量及氨基酸组成,对反刍动物氨基酸营养及其氨基酸模式有重要影响。     

过瘤胃氨基酸的作用与应用

反刍动物蛋白质营养的实质和核心是氨基酸营养,由于瘤胃微生物的作用,反刍动物日粮中直接添加氨基酸,会在瘤胃中部分或完全降解,最终到达小肠可被吸收利用的氨基酸量减少。因此氨基酸过瘤胃保护非常重要。许多研究表明,在日粮中添加过瘤胃氨基酸（Rumen—Protected Amino Acids,RPAA）是为反刍动物提供理想小肠氨基酸简便、直接而又有效的调控方法,对提高饲料利用率、减少蛋白质和氨基酸浪费、降低生产成本、提高高产反刍动物生产性能具有重要意义。     

过瘤胃保护氨基酸研究进展

随着反刍动物蛋白质和氨基酸消化代谢研究的不断深入，计算机预测模型的发展，通过日粮配合来调控小肠氨基酸供应以满足反刍动物氨基酸需求成为可能。许多研究表明，在日粮中添加瘤胃保护性氨基酸（rumen protected amino acid）是为反刍动物提供理想小肠氨基酸简便、直接而又有效的调控方法，对提高饲料利用率、减少蛋白质和氨基酸浪费、降低生产成本、     

过瘤胃蛋白和氨基酸对奶牛、绵羊干物质采食量、消化率和生长性能的影响

数量充足和配比合理的营养对家畜生产性能起着决定性作用,其中蛋白质是动物生长发育、繁殖性能的主要限制因素之一。蛋白质的种类和水平决定着动物机体组成及日粮中必需氨基酸的供应。对反刍动物来说,蛋白质的作用是双方面,既要满足瘤胃厌氧微生物发酵的需要,又要满足动物成长的营养需要。然而,由于瘤胃的发酵作用,日粮中绝大多数蛋白质在瘤胃内被降解(称为瘤胃降解蛋白,RDP),只有小部分能通过瘤胃在小肠内吸收(称为非瘤胃降解蛋白,RUP),因此用于厌氧合成微生物蛋白的RDP以及RUP的种类决定了反刍动物日粮和机体必需氨基酸的利用率。微生物蛋白和过瘤胃蛋白决定了高产动物日粮中必需氨基酸的供应。因此,饲喂过瘤胃蛋白和氨基酸被认为是满足反刍动物生理以及生产需要的有效方法。文章综述了过瘤胃蛋白、过瘤胃赖氨酸和过瘤胃蛋氨酸在反刍动物上的应用,以及对奶牛、绵羊干物质采食量、消化率、生产性能影响的研究。蛋白质是反刍动物重要的限制性营养,由RDP和RUP组成。瘤胃微生物通过将RDP降解成小肽、氨基酸和氨等来合成微生物蛋白,其数量主要受日粮中瘤胃发酵率的制约。因此,RDP和RUP或氨基酸的供应对于满足反刍动物营养需要非常重要,尤其是对于饲喂低水平日粮的反刍动物。添加瘤胃保护蛋白和瘤胃保护氨基酸(特别是赖氨酸和蛋氨酸)能提高奶牛、绵羊的干物质采食量和消化率。同时,还能够提高生长性能、繁殖效率和产奶量。不管是单独添加,还是与赖氨酸同时添加,如果蛋氨酸的添加量大于肠道的可消化吸收量时,则有可能会产生负面影响。在奶牛泌乳早期的低蛋白水平日粮中添加蛋氨酸,能避免奶牛长期的不良反应。总而言之,反刍动物在低营养水平下添加瘤胃保护蛋白质和氨基酸,能提高饲料采食量、消化率以及生长性能。     

反刍动物蛋白质的营养及研究进展(续)

4　反刍动物氨基酸的营养与研究进展4 .1　反刍动物氨基酸的代谢氨基酸是组成蛋白质的基本单位 ,从很大程度上说 ,蛋白质的营养就是氨基酸的营养 ,对于反刍动物来说也不例外。反刍动物体内氮的来源有 4个途径 ,即通过瘤胃壁吸收的氮、小肠吸收的瘤胃微生物氮、瘤胃非降解蛋白质     

粗饲料氨基酸在瘤胃内降解规律研究

由于粗饲料在反刍动物日粮中占有相当大的比例 ,因此对粗饲料营养价值的评定具有十分重要的意义。现代反刍动物营养理论认为 ,饲料蛋白质进入瘤胃后 ,约有 70 %被瘤胃微生物降解用于合成菌体蛋白质 ,同时也会造成饲料氨基酸氮的损失 (李建国等 ,1 999)。小肠蛋白质 (氨基酸 )营养调控的主要目标是提高进入小肠的氨基酸数量 ,改进其平衡 ,而饲料小肠氨基酸量取决于瘤胃降解率及其氨基酸量。目前对粗饲料降解后残渣中的氨基酸含量研究较少 ,现有的一些研究表明 ,精饲料在瘤胃降解后残渣中的氨基酸含量可采用未降解前的氨基酸含量参数 ,而粗饲…     

反刍动物过瘤胃蛋白保护技术

反刍动物所需营养中蛋白质来源有两个,一是通过微生物降解合成的菌体蛋白,一是过瘤胃蛋白,而日粮中绝大多数蛋白质在瘤胃内被降解浪费掉了,只有过瘤胃蛋白能够在小肠内被充分地消化吸收。因此,为了增加过瘤胃蛋白比例,提高饲料的利用率,就目前饲料蛋白的各种保护技术和效果进行了阐述。     

饲料蛋白质在反刍动物瘤胃的降解及其影响因素

由于瘤胃细菌和原虫的作用,反刍动物利用蛋白质明显不同于单胃动物。饲料蛋白质进入瘤胃后,一部分被微生物降解为非蛋白氮,与饲料中原有的以及唾液中的非蛋白氮最终一起转变为氨。瘤胃微生物利用发酵生成的挥发性脂肪酸等作为碳架,并利用瘤胃发酵释放的能量(ATP)将氨合成微生物蛋白。微生物蛋白连同饲料蛋白质中的未降解部分(过瘤胃蛋白质),随着食糜流动进入真胃和小肠,被动物分泌的消化液(酶)分解为氨基酸,为动物体吸收和利用。大量研究表明,优质饲料蛋白质经过保护后,就能够满足高产反刍动物对过瘤胃蛋白质的需要,提高优质植物性蛋白质利用效率,动物的氮沉积及生产性能得到明显改善,同时根据瘤胃能氮平衡理论为在日粮中利用更多的非蛋白氮提供了可能。了解饲料蛋白质在反刍动物瘤胃的降解及其影响因素,可为制定过瘤胃蛋白质、氨基酸的技术措施提供依据。     

反刍动物蛋白质营养调控新技术

反刍动物蛋白质营养研究已有100多年的历史,随着反刍动物蛋白质营养领域应用研究方面的不断深入与发展,反刍动物日粮中蛋白质的营养调控技术也日趋成熟。本文将从消化道和组织两个层次就反刍动物日粮中的蛋白质营养调控新技术进行阐述。1　反刍动物蛋白质代谢特点反刍动物的蛋白质代谢,因受瘤胃发酵的影响,其蛋白质消化代谢与单胃动物明显不同。一般认为,当饲料蛋白质被采食进入瘤胃后,一部分被微生物降解为寡肽、氨基酸和氨,瘤胃微生物可以利用发酵生成的挥发性脂肪酸作碳架,并利用发酵释放的能量(ＡＴＰ),将部分寡肽、氨基酸和氨又重新合…     

日粮蛋白水平和过瘤胃蛋氨酸对奶牛泌乳性能及采食量的影响

正目前,世界各国在发展反刍动物生产中,普遍受到蛋白质饲料资源紧缺的限制,同时也存在反刍动物对含氮资源利用率偏低的问题。蛋白质是影响奶牛生产性能的主要营养物质之一,蛋白质对反刍动物的生物学效价取决于小肠可消化蛋白,虽然瘤胃微生物能合成一定数量的菌体蛋白来满足奶牛正常生理需要,但难以满足高产奶牛对蛋白质和氨基酸的需要量。通过高蛋白水平日粮来补充蛋白质的做法一直以来是多数中小规模奶牛场的常规日粮调整办法。     

Site and extent of digestion and amino acid flow to the small intestine in beef cattle consuming limited amounts of forage

Eight Angus x Gelbvieh heifers (445 +/- 74.5 kg) fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square double double-crossover designed experiment to assess the effect of restricted forage intake on site and extent of digestion and flow of essential AA amino acids to the small intestine. Heifers were fed chopped (2.54 cm) bromegrass hay (9.2% CP, 64% NDF on an OM basis) at one of four percentages of maintenance (30, 60, 90, and 120%). Experimental periods were 21 d in length, with 17 d of adaptation followed by 4 d of intensive sample collection, after which maintenance requirements and subsequent level of intake were adjusted for BW change. True ruminal OM, NDF, and N digestion (g/d) decreased linearly (P < 0.001) with decreasing forage intake. When expressed as a percentage of OM intake, true ruminal OM and N digestibility were not affected (P = 0.23 to 0.87), whereas ruminal NDF digestibility tended to increase (P = 0.09) as forage intake decreased. Total and microbial essential amino acid flow to the duodenum decreased linearly (P = 0.001) from 496.1 to 132.1 g/d and 329.1 to 96.0 g/d, as intake decreased from 120 to 30% of maintenance intake, respectively. Although the profile of individual essential amino acids in duodenal digesta (P = 0.001 to 0.07) and isolated ruminal microbes differed (P = 0.001 to 0.09) across treatment, the greatest difference noted for total and microbial essential amino acid profile was only 0.3 percentage units. Because total and microbial flow of essential amino acids to the small intestine decreased as OM intake decreased, but true ruminal degradability of individual essential amino acids (P = 0.17 to 0.99) and digesta essential amino acid profile were comparable across treatments, total essential amino acid supply to the small intestine was predicted using OM intake as the independent variable. The resulting simple linear regression equation was: total essential amino acid flow = (0.055 x OM intake) + 1.546 (r2 = 0.91). The model developed in this experiment accounted for more of the variation in the data set than the current beef cattle NRC model, which under-predicted total flow of essential amino acids to the duodenum. The prediction equation developed herein can be used to estimate the supply of essential amino acids reaching the small intestine when formulating supplements to compensate for potential amino acid deficiencies resulting from restricted forage intake.     

瘤胃能氮同步释放对瘤胃微生物蛋白质合成的影响

瘤胃微生物蛋白质（microbial protein,MCP）是反刍动物小肠可吸收蛋白质（Pro）的主要来源,而优化瘤胃发酵调控,促进瘤胃微生物蛋白质的合成一直是反刍动物营养研究的热点问题。近年来,关于瘤胃能氮同步释放优化瘤胃微生物蛋白质合成方面的研究引起了关注,因此,作者主要从瘤胃能氮同步释放的概念、瘤胃能氮同步释放的评价方法和瘤胃能氮同步释放对瘤胃微生物蛋白质合成影响方面的研究作一简要评述。     

Effects of dietary energy level and protein source on nutrient digestion and ruminal nitrogen metabolism in steers.

Four Simmental steers with ruminal, duodenal, and ileal cannulas were used to examine effects of dietary forage: concentrate ratio and supply of ruminally degradable true protein on site of nutrient digestion and net ruminal microbial protein synthesis. Steers (345 kg) were fed ammoniated corn cob (high forage; HF)- or corn cob/ground corn/cornstarch (low forage; LF)-based diets supplemented with soybean meal (SBM) or a combination of corn gluten meal and blood meal (CB). Diets were fed at 2-h intervals with average DM intake equal to 2.2% of BW. Feeding LF vs HF increased (P less than .05) OM digestion (percentage of intake) in the stomach, small intestine, and total tract. Efficiency of microbial CP synthesis (EMCP; g of N/kg of OM truly fermented) decreased (P less than .05) for LF vs HF (24.1 vs 26.8), but microbial N and total N flows to the small intestine were similar (P greater than .05) between energy levels (average 112 and 209 g/d, respectively). Total N flows to the small intestine were 13.1% greater (P less than .05) for CB than for SBM because of increased (P less than .05) passage of nonmicrobial N. Feeding SBM vs CB increased (P less than .05) EMCP (27.3 vs 23.3) and microbial N flow to the small intestine (127.5 vs 112.5 g/d), but these increases were not likely due to increased ruminal concentrations of ammonia N (NH3 N). Decreased (P less than .05) incorporation of NH3 N into bacterial N and slower turnover rates of ruminal NH3 N for SBM vs CB suggest that direct incorporation of preformed diet components into cell mass increased when SBM was fed. Results of this study suggest that the inclusion of ruminally degradable protein in the diet may increase the supply of products from proteolysis and that this can increase EMCP and microbial protein flow to the small intestine.     

过瘤胃保护氨基酸提高奶牛乳蛋白转化效率的研究

为提高奶牛乳蛋白含量和饲料蛋白质用于产奶的转化效率,选择体况、胎次、泌乳期相近的中国荷斯坦奶牛27头,采用L9（34）正交试验设计,研究奶牛不同小肠可消化蛋白（IDCP）供应水平日粮添加过瘤胃保护氨基酸（RPAA）对乳蛋白率含量和IDCP转化为乳蛋白效率的影响。结果表明,IDCP按《中国奶牛饲养标准》（2004）推荐需要量92%水平供应,组合添加过瘤胃保护赖氨酸（RPlys）32 g/d＋过瘤胃保护蛋氨酸（RPmet）8 g/d,日粮干物质中NDF水平控制在37%～41%,可有效提高泌乳前期奶牛乳蛋白含量与IDCP用于泌乳的转化效率。     

Site of protein digestion in steers: predictability

The nature and predictability of protein digestion in steers were examined in a series of experiments. Bypass and intestinal digestion of supplemental proteins were measured with Angus steers (203 to 254 kg) fitted with dual reentrant intestinal cannulas. Daily feed intakes were 1.8 to 1.9% of body weight. Two trials were conducted with soybean meal, cottonseed meal, a hardened casein, meat meal and two different sources of dehydrated alfalfa meal fed with an 80% concentrate diet. In the third trial, digestion of soybean meal and cottonseed meal were measured with a 60% prairie hay diet. Estimates of ruminal escape or bypass were 43, 50, 36, 76, 57, 62, 24 and 43%, respectively. Results suggest that roughage level alters bypass. A standard reference system for predicting bypass based on measurements of N solubility and in situ disappearance rates was compared with measured bypass. The correlation between observed bypass to the small intestine and bypass predicted by this system was high (r = .91, P less than .01). Combining pepsin solubility, an indicator of true intestinal digestibility, with bypass estimated by the standard reference system, allowed us to predict N disappearance from the small intestine. Predicted and measured N disappearance of fed N from the small intestine were very close.     

赖氨酸席夫碱对到达绵羊小肠游离氨基酸和蛋白质流量的影响

选用4只体重在40 kg左右,安装永久性十二指肠瘘管的中国美利奴（新疆型）细毛羊,采用拉丁方设计,分别添加3.42和6.84 g赖氨酸席夫碱（分别含赖氨酸2、4 g）、2.56和5.12 g赖氨酸盐酸盐作为对照（分别含赖氨酸2、4 g）,以研究对进入绵羊小肠游离氨基酸和蛋白质流量的影响。结果表明,在赖氨酸实际添加水平都为4 g/d时,赖氨酸席夫碱使绵羊小肠液中游离Lys、Glu和Tyr的流量分别提高了25.17%、38.35%和33.88%（P<0.05）,对其他游离氨基酸流量的影响不明显。添加赖氨酸席夫碱对到达绵羊小肠的微生物蛋白质流量、过瘤胃蛋白质（瘤胃非降解蛋白）流量没有影响。添加赖氨酸席夫碱可提高到达绵羊小肠的游离赖氨酸量,且与添加量有关。     

饲粮能量和蛋白质水平对滩羊小肠中小肽和氨基酸转运载体mRNA表达量的影响

本试验旨在研究饲粮能量和蛋白质水平对滩羊小肠中小肽和氨基酸转运载体mRNA表达量的影响。选取112只健康、体重相近的滩羊,随机分成4组,每组4个重复,每个重复7只羊。标准水平的饲粮能量和蛋白质水平参考《肉羊饲养标准》(NY/T 816—2004),各组试验滩羊分别饲喂不同能量和蛋白质水平饲粮:0.84×标准水平(Ⅰ组)、0.96×标准水平(Ⅱ组)、1.08×标准水平(Ⅲ组)和1.20×标准水平(Ⅳ组)。试验根据羊体重分2个阶段:29~35 kg和36~40 kg。于每个阶段末,每个重复屠宰1只试验羊,取其小肠组织样,运用实时荧光定量PCR技术,研究小肽转运载体1(Pep T1)、y+型氨基酸转运载体1(CAT1)、兴奋性氨基酸转运载体3(EAAT3)mRNA表达量的变化。结果表明:1)在29~35 kg阶段末,小肠中Pep T1 mRNA的表达量随着饲粮能量和蛋白质水平的提高呈先下降再上升的趋势,Ⅱ组显著低于其他3组(P0.05);Ⅳ组小肠中CAT1 mRNA的表达量显著高于其他3组(P0.05);Ⅲ组小肠中EAAT3mRNA的表达量显著高于其他3组(P0.05)。2)在36~40 kg阶段末,Ⅱ组小肠中Pep T1mRNA的表达量显著高于其他3组(P0.05);Ⅱ组小肠中CAT1 mRNA的表达量显著高于Ⅲ组(P0.05);小肠中EAAT3 mRNA的表达量随着饲粮能量和蛋白质水平的提高呈上升趋势,Ⅲ组和Ⅳ组小肠中EAAT3 mRNA的表达量显著高于Ⅰ组和Ⅱ组(P0.05)。由此可见,饲粮能量和蛋白质水平会影响滩羊小肠中Pep T1、CAT1、EAAT3 mRNA的表达量,使机体对小肽和氨基酸的吸收利用率随之改变,以适应滩羊的生长发育。     

Evaluation of dairy food processing wash water solids as a protein source: III. Nitrogen utilization by heifers fed medium-concentrate diets

Eight multicannulated heifers (average BW 415 +/- 34 kg) were used in a replicated 4 x 4 Latin square to evaluate fluid milk processing wash water solids (WWS) as a dietary N source. Heifers were fed corn/cottonseed hull-based diets containing soybean meal (control, 0% WWS N) or WWS replacing soybean meal at 33, 67, or 100% of supplemental dietary N. Total tract and ruminal DM and OM digestibilities decreased linearly or cubically (P less than .05) as dietary WWS N increased. Total ruminal VFA concentration (P less than .05) and propionic acid molar proportion (P less than .10) were greater in heifers fed 0 vs 100% WWS N. Heifers fed 0% WWS N had the greatest (P less than .05) ruminal ammonia concentration at all sampling times. Dietary WWS did not affect (P greater than .10) ruminal pH, fluid dilution rate, fluid flow, fluid volume, or turnover time. Total tract N digestibility decreased quadratically (P less than .10) with increasing WWS N in the diet. Supplemental WWS N did not affect (P greater than .10) flow of duodenal ammonia N or bacterial N, or efficiency of microbial N synthesis. Diets containing WWS N resulted in a cubic increase (P less than .10) in duodenal flow of essential amino acids compared with 0% WWS N; however, there were no differences in small intestinal amino acid disappearance. Data indicate that WWS can replace 33% of the soybean meal N in a corn/cottonseed hull-based diet without decreasing ruminal fermentation, fluid digesta kinetics, microbial efficiency, or small intestinal amino acid utilization.     

Effect of Fusarium toxin-contaminated triticale and forage-to-concentrate ratio on fermentation and microbial protein synthesis in the rumen

In this study, the effect of Fusarium toxin-contaminated triticale (FUS) at high (60%) and low (30%) concentrate proportion in ruminant rations on ruminal fermentation, microbial protein synthesis and digestibility was investigated, using in vivo and in vitro methods. Significant effects of the forage-to-concentrate ratio on ruminal degradation and digestibility of crude nutrients and detergent fibre fractions as well as on the pH value and the concentration of short chain fatty acids (SCFA) in rumen fluid were found. The production of SCFA was affected, and the degradation of crude fibre and neutral detergent fibre in the rumen was reduced by the inclusion of FUS at high concentrate proportion. The efficiency of microbial crude protein synthesis was higher in diets with 60% than in diets with 30% concentrates, but was impaired in the presence of FUS in vitro at the high concentrate level. Marginal effects of FUS on the amino acid pattern of microbial protein were detected. It was concluded that the use of FUS in high concentrate diets can influence ruminal fermentation and microbial protein synthesis at a dietary deoxynivalenol concentration below 5 mg/kg dry matter.     

奶牛小肠蛋白质体系的局限性与氨基酸平衡

现在国内外已将奶牛的可消化粗蛋白体系改进为小肠可消化蛋白质体系,但由于小肠蛋白质的氨基酸组成变异性很大,其CV高达5.6%~19.2%,因而导致可代谢蛋白质的转化效率不稳定,表观效率便会掩盖实际需要。奶牛的第一和第二限制性氨基酸分别为赖氨酸和蛋氨酸,较多研究认为组氨酸为第三限制性氨基酸,但当肝后部提供的组氨酸不能满足产奶需要时,组氨酸可来自体储存的分解,因此尚不能完全确定。据对87个试验结果的统计分析表明,在瘤胃后供给额外的赖氨酸和蛋氨酸,则奶牛的产奶量、乳蛋白量、乳蛋白率均明显增加;对48个试验结果的统计分析结果表明,在可代谢蛋白质被满足供应的基础上,当赖氨酸和蛋氨酸分别达到7.08%和2.35%时,乳蛋白质产量达到最高点。法国INRA在其试验的基础上,确定小肠可消化真蛋白质中的赖氨酸和蛋氨酸的适宜含量为7.3%和2.5%,由于我国现行的是小肠可消化粗蛋白质体系,故建议其赖氨酸和蛋氨酸的含量为6.0%和1.9%,但须评定瘤胃微生物蛋白质和饲料非降解蛋白质的赖氨酸和蛋氨酸含量,并调整日粮使其达到平衡。