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.     

Sodium transport across the isolated epithelium of sheep omasum is influenced by luminal ammonia

Ammonia is a physiological fermentation product in the forestomachs and is absorbed from the rumen and omasum. Cellular uptake of ammonia affects the intracellular pH of polar and non-polar cells. The effect of the uptake on the pH of the cytosol depends on the predominant form of ammonia. NH(3) uptake and its intracellular protonation tend to alkalinize the cytoplasm, whereas the uptake of NH(4)(+) acidifies the cytoplasm by reversing this reaction. Consequently, the absorption of ammonia across the omasal epithelium could cause a change of the intracellular pH and pH-dependent transport mechanisms like Na/H exchange. Because no information is available about the form of ammonia absorbed in the omasum and, hence, possible modulation of Na transport by ammonia, the effect of increasing luminal ammonia concentrations (0, 5, 15 and 30 mmol/l) on Na transport were studied. In epithelia of hay-fed animals, ammonia linearly inhibited Na transport in a dose-dependent manner, at a luminal pH of 7.40, but not at a pH of 6.40. Ammonia did not influence Na transport in epithelia of concentrate-fed animals. Because luminal ammonia did not consistently change the short circuit current or tissue conductance absorption of ammonia as NH(4)(+) appears to be unlikely. The predominant form of ammonia absorbed in the omasum is probably NH(3), which is protonated in the cytosol. The reduced availability of protons may be the cause of inhibition of Na transport via Na/H exchange.     

高谷物日粮促进山羊瘤胃上皮单羧酸转运蛋白1及钠钾ATP酶mRNA的表达

本试验旨在研究高谷物日粮对山羊瘤胃上皮形态结构及单羧酸转运蛋白(monocarboxylate transporter, MCT)和钠钾ATP酶mRNA表达的影响。将10头装有永久性瘤胃瘘管的健康阉割公山羊随机分为饲喂全粗料日粮的对照组(Hay,0%谷物,n=5)和饲喂高谷物日粮的处理组(HG,65%谷物,n=5),试验期为7周。试验开始后,于每周晨饲后的0、2、3、4、6、8和12 h连续采集瘤胃液监测瘤胃pH值的变化,收集其中第0、3、6和12 h的瘤胃液待测挥发性脂肪酸(volatile fatty acid, VFA)浓度。试验的第50天,屠宰采集瘤胃上皮用于形态学及基因定量分析。研究结果显示:与全粗料组山羊相比,高谷物组山羊瘤胃pH值、乙酸浓度及乙丙比都显著下降(P<0.001),而瘤胃丙酸浓度、丁酸浓度及其他VFA浓度都显著升高(P<0.001);高谷物日粮组的瘤胃乳头长度显著高于对照组(P=0.001),瘤胃乳头宽度显著低于对照组(P<0.001),但是两组间的瘤胃乳头表面积并无显著差异;透射电镜结果显示,长期饲喂高谷物日粮导致瘤胃上皮细胞线粒体发生降解;实时定量PCR结果表明,与对照组相比,高谷物日粮显著升高了MCT1(P<0.001)和钠钾ATP酶(P=0.001)的mRNA表达量,显著降低了MCT4的mRNA表达量(P=0.041),但对MCT2的表达没有显著影响(P=0.305);进一步分析这些基因的mRNA表达量与pH值和VFA浓度之间的相关性,结果显示,MCT1和钠钾ATP酶的mRNA表达量与瘤胃pH值和乙酸浓度呈显著负相关,与总VFA、丙酸、丁酸的含量呈显著正相关,而MCT4的mRNA表达量与pH值呈显著正相关,与总VFA、丙酸、丁酸的含量呈显著负相关。以上结果提示:高精料引起的瘤胃pH值下降和VFA的变化可能与瘤胃上皮MCT和钠钾ATP酶表达量的变化相关。研究结果对深入认识高谷物饲喂引发的瘤胃功能紊乱具有重要意义。     

Effect of a hay and a grain diet on the rate of hydrolysis of ochratoxin A in the rumen of sheep

The hydrolysis of ochratoxin A (OA) and the corresponding formation of its hydrolysis product, alpha ochratoxin (O alpha), by ruminal digesta and in the rumen of hay-fed and grain-fed sheep were compared. Ruminal contents from sheep fed diets with hay or with grain hydrolyzed OA in vitro; the majority of the activity was associated with the particulate fraction of the ruminal contents. The rate of hydrolysis of OA by ruminal fluid that was adjusted to different pH values was not influenced (P greater than .6) by the pH of the samples (pH was from 5.5 to 7.0). Ruminal fluid obtained from hay-fed animals (pH 7.0) was able to hydrolyze OA in vitro and to produce the hydrolyzed product, O alpha, at a much greater rate (fivefold) than ruminal fluid obtained from grain-fed animals (pH 5.5) (P less than .01). Ochratoxin A was administered intraruminally at a concentration of .5 mg/kg of BW to hay-fed and grain-fed sheep. The half-lives for disappearance of OA from the rumen of sheep fed grain (normal feed intake, rumen pH 5.7), fed grain at a low level (30% of normal feed intake, pH 6.5), and fed hay (pH 7.1) were 3.6, 1.3, and .6 h, respectively. The results suggest that OA is hydrolyzed much faster in the rumen of sheep fed hay than in sheep fed grain, presumably because of the different ruminal microbial population, which in turn influenced the rate of hydrolysis of OA.     

Water absorption in relation to fermentation in the colon of the ostrich (Struthio camelus)

The colon is a major site for fermentation and water absorption in the ostrich. Water absorption along the colon was evaluated and its relationship to osmolality, Na+ concentration, short chain fatty acid (SCFA) concentration and carbohydrate content of digesta analysed. Mean water content decreased from 5.30 +/- 0.99 to 2.51 +/- 0.13 mf/g dry mass in the first 5 m of the colon. Correspondingly, mean carbohydrate content fell from 529.85 +/- 46.61 to 434.99 +/- 29.89 mg/g dry mass. A significant correlation was shown between the decreases in mean carbohydrate and water content along the colon (r2 = 0.997, P < 0.05). Changes in mean osmolality (+/- 10 mOsm/kg) and SCFA concentration (+/- 7 mmol/l) were minimal in comparison to the change in Na+ concentration (-54 mmol/l). These findings reflect a close coupling between SCFA production and absorption on the one hand and water absorption on the other.     

Influence of food deprivation on the transport of 3-O-methyl-alpha-D-glucose across the isolated ruminal epithelium of sheep

Recent studies provided evidence that the ruminal epithelium is able to absorb D-glucose even at physiologically low intraruminal concentrations. To elucidate whether ruminal D-glucose transport shows adaptive responses during food deprivation, transport of 3-0-methyl-alpha-D-glucose (3-OMG), a hardly metabolizable D-glucose analogue, was measured in isolated ruminal epithelia obtained from hay-fed or food-deprived adult sheep. In both groups, a significant net absorption of 3-OMG to the serosal side (in vivo: blood side oriented) could be detected at 3-OMG concentrations between 0.25 mM and 5 mM. Net absorption of 3-OMG was abolished by mucosal (in vivo: lumen side oriented) addition of phlorizin, an inhibitor of the sodium glucose-linked transporter 1 (SGLT-1). Net absorption of 3-OMG followed Michaelis-Menten kinetics, but apparent affinity and maximal transport capacity were lower in epithelia obtained from food-deprived sheep. In contrast to the decrease of the (secondary) active 3-OMG transport, serosal-to-mucosal permeation of 3-OMG increased after food deprivation, suggesting an elevated passive 3-OMG transfer. It is concluded that the altered transport characteristics are either part of a global energy-sparing process during food deprivation (i.e., a lowered activity of the Na+/K+-ATPase) or result from specific down-regulation of SGLT-1.     

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.     

Effect of supplementation of rice bran and fumarate alone or in combination on in vitro rumen fermentation,methanogenesis and methanogens

This study investigated the effect of fumarate (FUM) and rice bran (RB), alone and together, on in vitro rumen fermentation, methanogenesis and methanogens. In vitro incubation was performed with six media that were either unsupplemented (control) or supplemented with 10% RB, 5 mmol/L FUM, 10% RB + 5 mmol/L FUM, 10 mmol/L FUM, or 10% RB + 10 mmol/L FUM. Methane (CH₄) production, dry matter digestibility, CH₄ per digested dry matter, total short‐chain fatty acid (SCFA) production, proportion of SCFA, acetate : proprionate ratio, production of NH₃‐N, and population density of rumen microbes were determined. Supplementation with 10% RB + 10 mmol/L FUM yielded a 36% decrease in CH₄ production compared to the control. Supplementation of FUM, in the presence or absence of RB, provided increases in total SCFA production and propionate proportion up to 61% and 31%, respectively. Total bacteria, methanogens and protozoa populations were significantly (P < 0.05) decreased with the 10% RB + 10 mmol/L FUM supplementation. The effect of anti‐methanogenesis of FUM was enhanced by the addition of RB. Notably, the CH₄ production attenuation was achieved by 10% RB + 10 mmol/L FUM without reduction of digestibility or of ruminal fermentation.     

Development of rumen fermentation in calves during milk feeding]

The concentration of total volatile fatty acids (VFA) in the rumen fluid were increasing with the age of the animals (Fig. 1). A significant increase in the concentrations of total VFA (P less than 0.01) from 70.93 to 90.71 mmol/l was observed in the age period of 5-7 weeks and a highly significant increase (P less than 0.001) in the age period of 9-11 age. At the average age of seven weeks the lower boundary of the reference value range (80-120 mmol) of the total VFA concentrations in the rumen fluid as mentioned for adult animals was exceeded in the experimental calves. As to this parameter in individual calves, the level of the total VFA concentrations in the rumen fluid of adult animals was not reached in 50% of calves at the age of three weeks, in 80% of calves at the age of five weeks, in 20% of calves at the age of seven weeks and in 10% calves at the age of nine weeks. At the age of 11 weeks the concentrations of total VFA reached the level of adult animals in all experimental animals (Fig. 2). The molar proportion of acetate (Fig 3) decreased from 74.04 mol% at the age of three weeks to 67.54 mol% at the age of 11 weeks, and the propionate proportion increased from 16.73 to 19.53 mol% within the same interval.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipogenesis and adipose tissue cellularity in steers switched from alfalfa hay to high concentrate diets

An experiment was conducted to 1) evaluate the effects of diet (alfalfa hay vs high concentrate) on adipose tissue cellularity and rates of in vitro lipogenesis and 2) determine if there was a relationship between in vitro lipogenic rates from acetate and lactate and rates of L- or D-lactate disappearance from plasma. Number of adipose cells/g of tissue decreased with time on experiment; however, hay-fed steers had fewer, but larger cells/g of subcutaneous adipose tissue compared with concentrate-fed steers (.78 +/- .04 vs 1.20 +/- .13 X 10(-6)/g, respectively). These results, however, are likely due to a higher (approximately 25%) intake of dry matter and metabolizable energy by the hay-fed steers. Carcass data obtained at slaughter (460 kg) indicated that the concentrate-fed steers had as much or more adipose tissue compared with the hay-fed steers. Characteristics describing D- or L-lactate disappearance from plasma were not highly correlated with lactate utilization for fatty acid synthesis. Utilization of acetate as a substrate for fatty acid synthesis in vitro was correlated (r = .64) with the rate of lactate utilization for fatty acid synthesis.     

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。     

藏绵羊暖、冷季瘤胃微生物菌群密度与其短链脂肪酸浓度互作分析

针对藏绵羊暖、冷季营养供给严重不均衡的生产实际,本试验旨在解析藏绵羊应对冷季营养严重匮乏的适应机制。试验选择1周岁(±1月龄)健康的放牧藏绵羊母羊12只,采用气相色谱仪和荧光定量PCR仪分别测定藏绵羊暖(7月)、冷(12月)季瘤胃短链脂肪酸(SCFA)浓度和微生物菌群密度,分析藏绵羊暖、冷季瘤胃SCFA浓度与微生物菌群密度间的互作关系。结果表明:藏绵羊冷季瘤胃中乙酸与丙酸浓度及比值(A/P)显著高于暖季(P<0.05),其他SCFA浓度在暖、冷季间差异不显著(P>0.05);各种SCFA所占比例分析发现,乙酸比例在冷季显著高于暖季(P<0.05),丁酸比例在暖季显著高于冷季(P<0.05),异丁酸比例在暖、冷季间差异不显著(P>0.05)。随着季节的变化,藏绵羊瘤胃微生物中黄色瘤胃球菌(Ruminococcus flavefaciens)、白色瘤胃球菌(Ruminococcus albus)、产琥珀酸丝状杆菌(Fibrobacter succinogenes)、溶纤维丁酸弧菌(Butyrivibrio fibrisolvens)、嗜淀粉瘤胃杆菌(Ruminobacter amylophilus)与产甲烷菌(Methanogenic bacteria)的相对密度在暖季显著高于冷季(P<0.05)。相关性分析表明,乙酸浓度与黄色瘤胃球菌相对密度,丙酸浓度与白色瘤胃球菌相对密度呈极显著正相关(P<0.01),乙酸浓度与白色瘤胃球菌、嗜淀粉瘤胃杆菌、溶纤维丁酸弧菌、产甲烷菌相对密度,丙酸浓度与产琥珀酸丝状杆菌相对密度呈显著负相关(P<0.05),丁酸浓度与6种微生物菌种相对密度无显著相关性(P>0.05)。由此可见,藏绵羊瘤胃微生物菌群密度与SCFA浓度间的互作存在明显差异,这种互作机制可能在藏绵羊应对暖、冷季的适应性方面发挥着重要作用,研究结果将为藏绵羊产业发展及种质资源保护利用提供参考。     

Suppressing effects of short-chain fatty acids on growth hormone (GH)-releasing hormone-induced GH release in isolated anterior pituitary cells of goats.

The involvement of tetrodotoxin-sensitive Na+ channels and receptor-operated nonspecific Ca2+ channels, and the effects of short-chain fatty acids, on growth hormone (GH) release induced by GH-releasing hormone (GHRH) were investigated in cultured and freshly isolated caprine anterior pituitary cells. In 3-d cultured cells in Dulbecco's modified Eagle's medium, an increase in GH release induced by GHRH (10 nmol/l) was moderately, but significantly, reduced by a voltage-sensitive Na+ channel antagonist tetrodotoxin (1 micromol). The GHRH-induced GH increase, which was not affected by a simultaneous addition of a receptor-operated nonspecific Ca2+ channel antagonist tetramethrine (0.1 mmol/l), was significantly reduced by a voltage-sensitive L-type Ca2+ channel antagonist nifedipine (1 micromol/l). Propionate and butyrate at 10 mmol/l, however, not only suppressed basal GH release but also significantly reduced the GH increase induced by 10 nmol/l of GHRH. The inhibitory action of these acids was also reproduced by an addition of beta-hydroxy butyrate (10 mmol/l) and octanoate (10 mmol/l). In freshly isolated and perifused cells, butyrate (10 mmol/l) as well as somatostatin (100 nmol/l) significantly reduced the GH increase induced by GHRH. From these findings we conclude that tetrodotoxin-sensitive Na+ channels and voltage-dependent L-type Ca2+ channels are involved in the cellular mechanism for GHRH-induced GH release, and that short-chain fatty acids such as propionate and butyrate have a direct action on somatotrophs to reduce basal and GHRH-induced GH release, in caprine somatotrophs.     

The effect of the early feeding of solid and bulk foods on the dynamic development of the digestive processes in calves ina large-scale breeding facility

Digestive activities were studied in test calves (n = 12) in relation to age and feed intake. The calves were isolated after birth from adult cows. Since the 14th day of age, milk replacers were fed with concentrate feed mixture TG and alfalfa hay, i.e. the calves were in the period of plant feeding. The investigation lasted from the end of milk feeding (50th day) to the age of six months. Overall health condition was studied clinically. The characteristics of digestive activities studied in rumen fluid at weekly--monthly intervals were pH, ammonia content, total content of volatile fatty acids, content of particular volatile fatty acids, incidence and number of infusoria. At the age of 50 days, actual pH of rumen fluid was on the average 6.07 and it ranged from 5.84 to 6.76 in the next period. Ammonia content was the highest at the age of 50 days (21.49 mmol/l rumen fluid), then it dropped to 9.83 mmol/l rumen fluid at the age of 180 days. The average total concentration of volatile fatty acids (C2-C5) made 117.00 mmol/l during the first examination, it increased to 132.98 mmol/l at the age of 84 days, and it dropped to 94.16 mmol/l rumen fluid at the age of six months. A similar tendency was found in the volatile fatty acids. The infusoria were found out only at the age of 120 days--their numbers were 155 000 per ml; at the age of 180 days their numbers rose to 368 000 per ml rumen fluid. No disorders of health condition were recorded during the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

采食后奶牛瘤胃短链脂肪酸及其吸收相关蛋白表达的研究

本试验旨在研究奶牛采食前后瘤胃中短链脂肪酸(SCFA)浓度的变化及其吸收相关蛋白表达量的差异。试验选用3头体重(720±30)kg且装有瘘管的健康荷斯坦牛(动物伦理审查编号为SXAU-EAW-2019-C002013),采食精粗比为40:60的日粮(10kg),试验预试期10d,于第11天饲喂前开始取样,采用气相色谱法检测奶牛采食前(0 h)和采食后(1、2、3、4、5、6、7、8 h)瘤胃液中SCFA浓度;并采用荧光定量PCR方法检测瘤胃上皮组织中与SCFA吸收相关的蛋白表达量。结果表明:在采食后1 h奶牛瘤胃中SCFA浓度最高(P<0.05);在采食后一段时间内(2~5h)与SCFA吸收相关蛋白表达量上调(P<0.05),AE2、MCT1基因表达量均在5 h最高,PAT1、NHE3基因表达量均在4 h最高,MCT4基因表达量在4、5、6h均较高,NHE1基因表达量在2h达到最高;AE2、MCT1、MCT4、NHE1基因表达量与SCFA浓度负相关或正相关(P<0.05),AE2、MCT1、MCT4基因表达量与瘤胃内pH正相关(P<0.05)。以上结果初步揭示,在采食后一定时间内,瘤胃中与SCFA吸收相关蛋白表达受SCFA浓度和pH的调节。     

Diurnal Patterns of Ruminal Concentrations and Portal Appearance Rates of Short-chain Fatty Acids in Sheep Fed a Hay or a Concentrate/Straw Diet in Two Meals Daily

Abstract

Three rumen fistulated and catheterized sheep were meal-fed and used to study ruminal and arterial concentrations of short-chain fatty acids (SCFA) as well as portal appearance rates of SCFA and irreversible loss rate (ILR) of acetate in 24 h periods on a hay and a concentrate/straw diet, respectively.

Ruminal and arterial concentrations as well as portal appearance rates of SCFA and ILR of acetate were significantly affected by the intake of feed. Generally, the highest concentrations and appearance rates were obtained 2 h after feeding. The portal recovery of arterial acetate was not affected by feeding or diet. The 24 h means were 0.68 ± 0.01 and 0.67 ± 0.01 on the hay and the concentrate/straw diet, respectively. Partial correlation coefficients corrected for the effects of time, sheep, and diet were calculated for the relationships evaluated. The portal appearance rate of acetate (r = 0.52, P <0.001) and the portal net appearance rate of propionate (r = 0.68, P <0.001) were linearly related to the ruminal concentrations of the two SCFA. The logarithm of the portal net appearance rate of butyrate seemed to be linearly related to the logarithm of the ruminal concentration of undissociated butyric acid (r = 0.70, P <0.001) when the effect of time was omitted from the model. The portal appearance rate of acetate (r = 0.22, P <0.05) and the portal net appearance rate of propionate (r = 0.63, P <0.001) as well as butyrate (r = 0.55, P <0.001) were linearly related to the arterial concentration of the respective SCFA. The results show that within animal and diet the ruminal as well as arterial concentrations are good predictors of SCFA portal appearance rates in sheep fed roughage at maintenance. Ruminal and arterial concentrations of SCFA seem less reliable predictors of portal appearance rates of SCFA between diets and sheep. The portal appearance of SCFA, 5.6 ± 0.5 and 7.0 ± 0.3 mol d^?1, accounted for 44 ± 4 and 43 ± 2% of the calculated metabolizable energy intake on the hay and the concentrate/straw diets, respectively.     

Rumen fermentation and histology in light lambs as affected by forage supply and lactation length

This study determined whether the rumen fermentation and histology traits may reflect the feeding strategy in light lambs (22-24 kg). Thirty-two single Rasa Aragonesa lambs were assigned to one of four treatments in a 2×2 factorial design. The factors were the inclusion of forage in the diet (alfalfa grazing vs. concentrate-fed indoors) and lactation length (weaning at 13 kg vs. suckling until slaughter). A multivariate canonical analysis discriminated individuals among feeding strategies. The main function differentiated weaned concentrate-fed lambs from the rest according to dorsal sac papillae height, ventral sac muscular layer thickness and the proportion of rumen valerate. The second function differentiated suckling concentrate-fed lambs from the rest according to plasma urea levels. Lactation length played an important role on rumen histology and protein utilization, especially in concentrate-fed lambs. Alfalfa grazing light lambs had similar rumen morphometric measures and fermentation characteristics, regardless of milk access.     

盐胁迫下外源Si对甘草种子萌发及幼苗K~+、Na~+含量的影响

以乌拉尔甘草(Glycyrrhiza uralensis)种子为试验材料,研究在NaCl(100和200mmol/L)胁迫下,不同浓度Si(0、0.4、0.8、1.2、1.6和2.0mmol/L)对种子萌发及幼苗根冠比和K~+、Na~+含量的影响。结果表明:外源Si对盐胁迫下种子的发芽率、发芽势和发芽指数均具有显著的促进作用,且Si浓度在0.4和2.0mmol/L下作用最佳;Si可显著增加幼苗的根冠比,幼苗可通过增加K~+吸收,减少Na~+吸收来维持根系内K~+、Na~+的平衡。     

Sulphur availability and microbial fermentation in the fauna-free rumen.

The concentration of H2S and rate of feed digestion, VFA and methane production in the rumen were measured in sulphur deficient (-S) and S supplemented (+S) sheep while fauna-free (-P) and after refaunation (+P). The concentration of rumen H2S was increased by S supplementation but was not affected by the presence of protozoa. When fauna-free, -S sheep had reduced rates of feed digestion (30 v 48%/d), acetate synthesis (35 v 115 g/d) and methane synthesis (0.4 v 7.4 g C/d) compared to +S sheep and up to 36% (v/v) of total rumen gas was H2. When these sheep were given a single dose of 8.8 g Na2SO4, the proportion of methane increased and the proportion of H2 in rumen gas decreased. After refaunation of sheep, their rates of feed digestion, VFA production and methane production were higher and were not affected by the level of S. From this differential response to S deficiency by -P and +P sheep, it is concluded rumen protozoa increase the availability of S to other rumen microbes. This is probably because they degrade protein through to peptides and amino acids.     

盐碱胁迫下黑麦草生长及离子微区分布特征

盐碱生境通过离子毒害和渗透胁迫等抑制植物的生长发育。离子微区分布调控主要通过调整盐分在不同部位的分布来减轻Na⁺等高浓度离子对重要组织器官的毒害作用,是盐碱胁迫下植物生存的重要策略之一。为探究黑麦草在盐碱胁迫下的离子微区分布特征,本研究通过水培法,采用不同盐碱浓度(0、50、100、200 mmol·L^-1)培养液处理黑麦草植株,考察其生长、离子吸收、运输选择性和微区分布变化,揭示黑麦草对盐碱胁迫的适应机制。结果表明:1) 盐碱胁迫下,植株的相对含水率、叶绿素含量逐渐降低,电解质外渗率显著升高;当盐碱浓度大于100 mmol·L^-1时,根长、株高和生物量均显著降低,即黑麦草的耐盐阈值是100~200 mmol·L^-1;2) 盐碱浓度为50 mmol·L^-1时,植株根中K⁺/Na⁺较空白升高了48.3%,Ca²⁺/Na⁺升高了54.1%,说明黑麦草根部可通过增强K⁺、Ca²⁺的吸收来维持细胞渗透压并缓解高浓度Na⁺的毒性;3) 在50~200 mmol·L^-1的盐碱浓度下,黑麦草叶片中可溶性组分及细胞壁中Na⁺的相对含量较对照显著增加,但细胞器内Na⁺的相对含量降低,说明叶部将Na⁺富集在液泡和细胞壁中,以减少Na⁺对细胞器的毒害作用;4) 叶片微观结构的SEM电镜图片显示,盐碱胁迫下叶片表皮增厚、导管数量减少和孔径缩小。综上所述,盐碱胁迫下黑麦草不同器官的适应机理不同,根部主要通过强化K⁺、Ca²⁺的吸收,降低对Na⁺的吸收,并将Na⁺区隔化在液泡中以降低离子毒害和维持渗透调节,而叶片主要通过将Na⁺区隔在液泡及细胞壁中,以及微观结构的变化来保护细胞器免受离子毒害。本研究可为黑麦草的耐盐碱适应机制及其在盐碱土上的种植提供理论依据。