反刍动物瘤胃上皮的结构特点

反刍动物的胃是复胃,与单胃动物的胃不同。反刍动物主要以瘤胃中发酵产生的短链脂肪酸(SCFA)作为机体的能量物质,而绝大部分的SCFA又通过瘤胃上皮直接吸收,为宿主供能。因此,深入了解瘤胃上皮结构特点有助于对其吸收功能进行深入的研究。笔者主要对瘤胃上皮的解剖学特点、细胞学特点及超微结构进行了综述。     

瘤胃上皮机械屏障的评定方法简

瘤胃上皮不仅是瘤胃微生物附着、生长并进行消化和代谢的主要部位，也是营养物质吸收、转运、代谢的主要场所，同时也是瘤胃内环境与血液循环系统之间的一道重要生理屏障。因此，维持瘤胃上皮结构和功能的完整性对保持反刍动物健康和生产性能具有重要意义。作者对循环式尤斯灌流系统的基本构造、注意事项及反刍动物瘤胃上皮机械屏障的评定方法进行了综述，旨在为维持瘤胃上皮屏障功能提供参考。     

MCT1在犊牛消化道的分布以及SCFA对MCT1表达的影响

短链脂肪酸(SCFAs)是由纤维素性饮食在瘤胃内发酵产生的乙酸、丙酸、丁酸以及戊酸等组成的混合物。SCFA对维持反刍动物的能量平衡至关重要,目前对SCFA的吸收机制和影响因素至今尚不清楚,本试验主要研究一元羧酸转运蛋白(monocarboxylate/proton cotransporter isoform 1,MCT1)在犊牛消化道内的分布及SCFA对MCT1表达的影响。运用免疫印迹Western blot和实时荧光定量PCR检测MCT1在犊牛消化道内的分布和表达;在体外试验中,体外添加一定比例的SCFA(乙酸、丙酸和丁酸的混合物)处理犊牛原代瘤胃上皮细胞,检测SCFA对MCT1表达水平的影响。结果显示:MCT1在整个消化道内均有分布,并且在瘤胃内的表达水平显著高于其他部位(P<0.01);体外处理的瘤胃上皮细胞,正常组MCT1的表达水平显著高于(P<0.05)SARA组。结果表明:正常水平的SCFA能够促进MCT1的表达和转运能力,而过量的SCFA抑制MCT1的表达和转运能力。     

反刍动物瘤胃上皮的生长发育及其调节

瘤胃是反刍动物消化代谢和营养吸收最重要的场所之一.瘤胃内分解产生的小分子营养物质大部分通过瘤胃上皮直接吸收,因而瘤胃上皮的生长发育和功能完善直接影响到反刍动物的生产性能.伴随着反刍动物机体的发育,从胎儿期到出生期直至成年,瘤胃上皮的形态结构及生理功能都在持续不断的发展和完善.其生长发育受到日粮营养水平(如日粮营养水平、饲料的精粗料比例、物理性质、代谢产物和饲喂制度等)、瘤胃内代谢产物(如短链脂肪酸、葡萄糖、多胺等)、神经内分泌(如胰岛素、胰岛素样生长因子-1、表皮生长因子、转化生长因子-α、胰高血糖素、生长激素、生长抑素等)等多重因素的影响.笔者主要对瘤胃上皮的生长发育过程及其调节因素进行了综述.     

动物瘤胃运动的影响因素及其调控措施

瘤胃是反刍动物对饲料进行消化吸收的重要器官,瘤胃通过和微生物相互结合,使反刍动物能够对高纤维的植物进行消化吸收。反刍动物的生理活动状态、饲料吸收程度以及对于瘤胃疾病的诊断都与瘤胃运动相联系。基于此,本文以反刍动物瘤胃运动为出发点,以其影响因素以及调控措施为主要内容,探究反刍动物瘤胃真菌特点以及反刍动物瘤胃运动的影响因素,并针对其反刍动物瘤胃特点,提出相应的运动的调控措施,以期为反刍动物瘤胃调控提供借鉴。     

高精料饲粮条件下反刍动物瘤胃适应机制的解析

饲喂高能、高淀粉饲粮是集约化生产中提高反刍动物生产性能的常用策略,但高精料饲粮易引起一系列的营养代谢疾病,其中以瘤胃酸中毒最为常见。反刍动物瘤胃不仅具有消化、吸收营养物质的功能,瘤胃上皮亦是重要的免疫屏障,故瘤胃健康对反刍动物至关重要。本文主要从反刍动物采食高精料饲粮时其瘤胃组织形态、瘤胃上皮适应分子机制和瘤胃微生物区系3个方面的变化进行阐述,以期为高精料饲粮条件下瘤胃适应机制的研究提供参考。     

反刍动物磷代谢动态分析

1 磷在反刍动物消化道中的消化和吸收 1.1 反刍动物前胃磷的消化和吸收 从消化道的起始端至十二指肠,磷酸盐的主要吸收部位存在着争论。Scott和Buchan(1987)在绵羊中用~(32)P标记法测定磷酸盐的吸收部位时,没有得到确切的结果。Edrise和Smith(1986)使用双重标记技术发现牛的瓣胃磷酸盐净吸收量是进入瓣胃量的10％～40％,绵羊胃磷酸盐的净吸收量大约是60mg/kg·d。BreBeard-Sworth等人(1989)利用隔离瘤胃上皮的方法,进行体内和体外法的研究也表明,瘤胃上皮有吸收无机磷酸盐的能力。另外,体内瓣胃上皮试验表明,磷酸盐的吸收是被动过程且需要依赖于电化学梯度的存在(Hotle等,1988)。而用未施手术的动物和在瘤胃施以“巴甫洛夫”胃动物的对比试验表明:瘤胃上皮对磷几乎是不可渗透的。由此可见,磷酸根离子在反刍动物的前胃存在着吸收,但吸收率较低。     

蛋氨酸羟基类似物(MHA)在反刍动物饲养中的应用

综述了蛋氨酸羟基类似物的主要特性和在反刍动物前胃的吸收、过瘤胃率和奶牛吸收情况，及对奶牛生产性能和在奶牛日粮中应用的优点。     

瘤胃发育研究进展

瘤胃是反刍家畜进行消化、吸收以及代谢的主要器官,瘤胃发育主要表现为瘤胃上皮和瘤胃乳头解剖结构以及生理功能的变化,而饲料组成和营养水平可在不同程度上影响其形态和功能,文章从影响瘤胃发育的要素、瘤胃上皮和乳头等方面对瘤胃发育进行概述。     

反刍动物瘤胃上皮发育规律及影响因素

瘤胃作为反刍动物特有的消化器官,在消化代谢中发挥着极其重要的作用,瘤胃上皮的发育和功能完善直接影响到反刍动物的生产性能,是提高生产效益的关键所在。文章旨在通过探讨反刍动物瘤胃上皮生长发育规律及其影响因素,为反刍动物营养生理研究积累资料。     

Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Highly fermentable diets are rapidly converted to organic acids [i.e., short-chain fatty acids (SCFA) and lactic acid] within the rumen. The resulting release of protons can constitute a challenge to the ruminal ecosystem and animal health. Health disturbances, resulting from acidogenic diets, are classified as subacute and acute acidosis based on the degree of ruminal pH depression. Although increased acid production is a nutritionally desired effect of increased concentrate feeding, the accumulation of protons in the rumen is not. Consequently, mechanisms of proton removal and their quantitative importance are of major interest. Saliva buffers (i.e., bicarbonate, phosphate) have long been identified as important mechanisms for ruminal proton removal. An even larger proportion of protons appears to be removed from the rumen by SCFA absorption across the ruminal epithelium, making efficiency of SCFA absorption a key determinant for the individual susceptibility to subacute ruminal acidosis. Proceeding initially from a model of exclusively diffusional absorption of fermentation acids, several protein-dependent mechanisms have been discovered over the last 2 decades. Although the molecular identity of these proteins is mostly uncertain, apical acetate absorption is mediated, to a major degree, via acetate-bicarbonate exchange in addition to another nitrate-sensitive, bicarbonate-independent transport mechanism and lipophilic diffusion. Propionate and butyrate also show partially bicarbonate-dependent transport modes. Basolateral efflux of SCFA and their metabolites has to be mediated primarily by proteins and probably involves the monocarboxylate transporter (MCT1) and anion channels. Although the ruminal epithelium removes a large fraction of protons from the rumen, it also recycles protons to the rumen via apical sodium-proton exchanger, NHE. The latter is stimulated by ruminal SCFA absorption and salivary Na(+) secretion and protects epithelial integrity. Finally, SCFA absorption also accelerates urea transport into the rumen, which via ammonium recycling, may remove protons from rumen to the blood. Ammonium absorption into the blood is also stimulated by luminal SCFA. It is suggested that the interacting transport processes for SCFA, urea, and ammonia represent evolutionary adaptations of ruminants to actively coordinate energy fermentation, protein assimilation, and pH regulation in the rumen.     

反刍动物体内尿素循环及其转运蛋白的分子调控机制研究进展

虽然在哺乳动物体内都存在尿素循环利用机制,但是反刍动物由于瘤胃的存在而使得尿素循环在维系机体氮平衡和提高氮素利用效率等方面发挥着更加重要的生物学意义。通过瘤胃壁扩散或转运,血液中的尿素可进入胃肠道,在脲酶的作用下转化为氨态氮,从而为瘤胃微生物蛋白合成提供氮源。研究表明,尿素在瘤胃上皮的自由扩散速度较慢,而尿素转运蛋白可以介导尿素分子高效地进行跨膜转运,其也被认为是反刍动物尿素循环最重要的调控因子。然而,相关报道已经证实,尿素转运蛋白的表达和功能发挥受到日粮营养水平与结构组成、瘤胃内环境、动物年龄等因素的影响。本文以尿素循环为出发点,重点阐述了反刍动物体内尿素循环的特点、影响因素以及尿素转运蛋白的表达特征及其分子调控过程,以期从分子生物学角度解析反刍动物尿素循环的作用机制,从而为生产实践中动物氮素的精准营养提供理论依据和技术支撑。     

日粮添加尿素对瘤胃上皮细胞增殖、凋亡以及吸收转运能力的影响

本研究探讨了在日粮中添加尿素替代部分豆粕对山羊瘤胃发酵、上皮细胞增殖、凋亡和吸收转运能力的影响。将18 只波杂山羊随机分为3 组（n=6）,分别饲喂3 种日粮：LC组（纯粗料）、MC组（30%精料）以及Urea组（1%DM缓释尿素替代部分豆粕+30%精料）。饲喂Urea组和MC组的山羊瘤胃中短链脂肪酸（SCFA）浓度、pH值均显著高于LC组,而该两组之间无显著差异;但Urea组在MC组的基础上进一步显著提高了瘤胃NH₃和血浆尿素氮（BUN）浓度。因此日粮添加尿素对于瘤胃上皮中受瘤胃SCFA浓度、pH值调节的上皮生长、细胞周期、增殖凋亡相关基因和SCFA转运载体mRNA表达的影响与MC组相似,但对受瘤胃NH₃调节的尿素转运、细胞内pH（pHi）调节相关蛋白mRNA表达则有显著的抑制效果,即显著高于LC组,但低于MC组。     

The effect of short chain fatty acids on calcium flux rates across isolated rumen epithelium of hay-fed and concentrate-fed sheep

The present in vitro experiment was conducted to study the effect of two concentrations of short chain fatty acids [SCFA: 0 (control), 40 and 100 mmol/l in the buffer solution on mucosal side] on calcium ion (Ca2+) transport across the isolated rumen epithelium of two groups of sheep. One group was subjected to hay ad libitum, whereas the other to concentrate feed (800 g per day in equal portion at 7.00 and 15.00 hours and hay ad lib). The conventional Ussing chamber method was used for measuring the Ca2+ transport rates (45Ca), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. The SCFA significantly increased Isc of the epithelia of concentrate-fed sheep. In both hay- and concentrate-fed animals, 45Ca flux rates showed an almost linear increase in net flux rate () with rising concentrations of SCFA, as a result of a combined effect of a large increase in mucosal-to-serosal flux rates () and an almost linear, but small, decrease in serosal-to-mucosal flux rate (). In concentrate-fed sheep and were significantly higher in tissues incubated with SCFA compared with hay-fed animals. The well-known adaptable morphological and functional changes in the rumen epithelium attributable to concentrate feeding obviously include Ca2+ transport; such feeding therefore may be considered as a possible prophylactic measure in the prevention of milk fever.     

反刍动物瘤胃发育规律及其调控机制研究进展

瘤胃是反刍动物至关重要的消化吸收器官，部分降解的营养物质可直接通过瘤胃上皮被机体吸收和利用。因此，瘤胃的发育程度与反刍动物的生产性能密切相关，而瘤胃发育充分且功能健全是反刍动物最佳生产性能得以发挥的前提条件。然而，幼龄反刍动物瘤胃的生理结构及其功能均发育不完善，需在固体饲料、断母乳等外界刺激下完成经由非反刍阶段向反刍阶段转变的复杂过程，进而才可发挥其重要功能。目前，如何掌握并遵循瘤胃的发育规律，在保证瘤胃充分发育且功能完善的情况下，对幼龄反刍动物实施早期断奶技术，已成为现代反刍动物养殖生产中亟需解决的问题之一。作者就反刍动物瘤胃发育进程中瘤胃微生物菌群的时空演变、瘤胃组织形态学发育和代谢改变及瘤胃发育调控机制进行综述，由生理结构至功能逐层对反刍动物瘤胃的发育规律进行全面总结，阐明影响反刍动物瘤胃发育的相关因素及其可能的调控机制。本文旨在进一步丰富与瘤胃发育相关的理论基础，以期为利用瘤胃发育规律开发促进反刍动物瘤胃发育的营养调控策略提供科学支撑，为挖掘幼龄反刍动物的生产潜力提供新思路。     

反刍动物瘤胃微生物酶类膜消化（触壁消化）的研究

本试验旨在探明反刍动物前胃内是否存在由微生物酶类参与的膜消化。在初生牛犊的前胃上皮,未发现蛋白酶和脲酶的活力。但在成年水牛和湖羊的前胃三室上皮,都不同程度地存在着这些消化酶。成年牛瘤胃还有上皮和腔之间尿素分解的正协同效应及纯化蛋白酶的上皮吸附效应,用15000倍扫描电镜观察,发现前胃上皮乳头表面有许多微突起,它们由可吸附酶分子的多糖层履盖,且成年动物的糖层较厚。由此推断,有活力的消化酶能借助于前胃的特殊结构,和与之接触的食糜发生膜消化。     

Modulation of Na+ transport across isolated rumen epithelium by short-chain fatty acids in hay- and concentrate-fed sheep

The effect of increasing concentrations of short-chain fatty acids [SCFA; mixture of the Na+ salts of acetic acid (62.5%), propionic acid (25.0%) and of butyric acid (12.5%)] on Na+ transport of sheep rumen epithelium was studied in vitro. The conventional Ussing chamber method was used for measuring Na+ transport rates (22Na+), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. SCFA in the buffer solution on the mucosal side caused a linear increase of Jnet Na+ from 1.14, to 1.22, 1.78 and 2.50 microeq/cm2/h in hay-fed sheep at 0, 15, 40 and 80 mmol/l SCFA, respectively. In a second study, the effect of higher SCFA concentrations [0 (control), 80, 100 and 120 mmol/l] was investigated with epithelia from two groups of sheep. One group was subjected to hay ad libitum, whereas the other received concentrate feed (800 g/day in equal portions at 7.00 am and 3.00 pm) and hay ad libitum. Epithelia from concentrate-fed sheep again showed a significant (p < 0.05) and linear increase in Jnet Na+ at 80, 100 and 120 mmol/l. However, in hay-fed sheep, the difference in increase among 80, 100 and 120 mmol/l SCFA was not significant, indicating that, above 80 mmol/l SCFA Jms and Jnet exhibit saturation. Moreover, Na+ fluxes (Jms and Jnet) were generally higher in concentrate-fed than in hay-fed sheep at all SCFA concentrations and significant differences were observed at 100 and 120 mmol/l SCFA. The obtained results confirm the effect of SCFA on Na+ transport and are in agreement with studies regarding feeding regimes and electrolyte transport in the rumen. The important new observation is the increase of Na+ transport in concentrate-fed sheep even at high concentrations of SCFA (100 and 120 mmol/l). The enhanced activity of the Na+/H+ exchanger at these SCFA concentrations supports the assumption that the capacity for regulating the intracellular pH by extrusion of protons is increased, suggesting an adaptation in concentrate-fed sheep. This adaptation could prevent possible disturbances of epithelial functions (transport and barrier) under conditions of increased SCFA absorption.     

Post‐natal changes in MCT1 expression in the forestomach of calves

The monocarboxylate transporter 1 (MCT1) has been demonstrated to be involved in the transfer of short‐chain fatty acids (SCFA) and/or their intraepithelial metabolites from the rumen to the blood. As MCT1 plays a role in SCFA transfer, it is assumed that SCFA are the main substrates influencing its expression. However, there are hints that MCT1 may also be expressed during the early life of the animal when SCFA are not released in the forestomach. To figure out whether MCT1 expression in the forestomach is influenced independently of SCFA during that period, we studied post‐natal MCT1 expression immunohistochemically in the epithelia of omasum, atrium ruminis, saccus dorsalis ruminis, saccus ventralis ruminis and reticulum of calves born preterm and at term. The calves were nourished by colostrum or by milk‐based formula diet. MCT1 could be found in all the forestomach compartments tested, even in preterm calves. The protein was mainly oriented to the luminal side in the immature epithelium 24 h after birth. Orientation to the blood side of the cells developed during the first 4 days after birth. In the rumen epithelia (but not in the other forestomach compartments tested), orientation of MCT1 to the blood side of the cells was paralleled by an increase in the overall expression rate during the first 4 days after birth. As lactate levels were very high directly after birth, a lactate‐dependent substrate induction may have been the underlying mechanism. However, non‐specific changes due to general differential processes might also be the cause. Both early upregulation of MCT1 and high blood lactate levels may provide the epithelia with lactate as energy source.