Forestomach epithelial receptor activation by rumen fluids from sheep given intraruminal infusions of volatile fatty acids

Forty-four reticuloruminal epithelial receptors were tested with rumen fluids obtained from 12 sheep before they were intraruminally infused with 4.0M acetic acid (8 sheep) or 4.0M butyric acid (4 sheep; preinfusion rumen fluid) and with rumen fluids obtained at the onset of ruminal stasis (abolition rumen fluid). The preinfusion rumen fluids from the 8 acetic acid-infused sheep (mean pH, 6.55) contained 1.7 mM nondissociated volatile fatty acids (VFA)/L and excited none of the 25 receptors tested. Preinfusion rumen fluids from the 4 butyric acid-infused sheep (mean pH, 6.98) contained 0.3 mM nondissociated VFA/L and also did not evoke responses in any of the 19 receptors tested. Abolition rumen fluids from sheep treated with acetic acid excited 17 of the 25 receptors tested and contained 89.4 mM nondissociated VFA/L, of which nondissociated acetic acid comprised 85.0 mM/L. Abolition rumen fluids from sheep treated with butyric acid activated 14 of the 19 receptors tested and contained 61.1 mM nondissociated VFA/L, of which 38.7 mM/L was nondissociated butyric acid. Preinfusion rumen fluids whose pH values were adjusted to that of abolition rumen fluids with HCl contained nondissociated VFA levels ranging from 16.3 mM/L (acetic acid-treated sheep) to 20.6 mM/L (butyric acid-treated sheep) and elicited responses in 4 of 30 receptors tested. Preinfusion rumen fluids whose pH values were adjusted to the pH value of abolition rumen fluid with acetic acid contained 29.5 mM nondissociated VFA/L and excited 7 of 13 tested receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Splanchnic metabolism of volatile fatty acids absorbed from the washed reticulorumen of steers

Six steers fitted with a ruminal cannula and chronic indwelling catheters in the mesenteric artery, mesenteric vein, hepatic portal vein, hepatic vein, as well as in the right ruminal vein were used to study metabolism of VFA absorbed from buffers in the emptied and washed reticulorumen. [2-(13)C]Acetate was infused into a jugular vein to study portal-drained visceral (PDV) uptake of arterial acetate, hepatic unidirectional uptake of acetate, and whole-body irreversible loss rate (ILR). Isobutyrate was infused into the right ruminal vein to calibrate VFA fluxes measured in the portal vein. On sampling days, the rumen was emptied and incubated in sequence with a 0-buffer (bicarbonate buffer without VFA), a VFA-buffer plus continuous intraruminal infusion of VFA, and finally another 0-buffer. Ruminal VFA absorption was determined as VFA uptake from the VFA-buffer and metabolic effects determined as the difference between metabolite fluxes with VFA-buffer and 0-buffers. Steady absorption rates of VFA were maintained during VFA-buffer incubations (4 h; 592+/-16, 257+/-5, 127+/-2, 17+/-<1, 20+/-<1 mmol/h, respectively, of acetate, propionate, butyrate, isovalerate, and valerate). The portal flux of acetate corrected for PDV uptake of arterial acetate accounted for 105+/-3% of the acetate absorption from the rumen, and the net portal flux of propionate accounted for 91+/-2% of propionate absorption. Considerably less butyrate (27+/-3%) and valerate (30+/-3%) could be accounted for in the portal vein. The sum of portal VFA and 3-hydroxybutyrate as well as lactate represented 99+/-3% of total VFA acetyl units and 103+/-2% of VFA propionyl units. Estimates are maximum because no accounting was made for lactate derived from glycolysis in the PDV. The net splanchnic flux of VFA, lactate, 3-hydroxybutyrate, and glucose accounted for 64+/-2% of VFA acetyl units and 34+/-5% of VFA propionyl units. Results indicate that there is a low "first-pass" uptake of acetate and propionate in the ruminal epithelium of cattle, whereas butyrate and valerate are extensively metabolized, though seemingly not oxidized to carbon dioxide in the epithelium but repackaged into acetate, 3-hydroxybutyrate, and perhaps other metabolites. When PDV "second-pass" uptake of arterial nutrients is accounted for, PDV fluxes of VFA, lactate, and 3-hydroxybutyrate represent VFA production in the gastrointestinal tract and thereby VFA availability to the ruminant animal.     

Effect of wood waste on the digestibility of glycides and level of volatile fatty acids in sheep]

Sheep were subject to an experiment concerning the effect of treated beech sawdust and thickened aqueous hydrolyzate of beech wood (xylocel) on the digestibility of glycides and on the level of volatile fatty acids (VFA) in the rumen content. The results prove that the use of treated beech sawdust as a replacer for ground barley straw favourably influenced the digestibility of monosaccharides, cellulose, lignin and total dry matter of the diet. Sawdust reduced the concentration of total VFA in the rumen content but the ratio of acetic acid to propionic acid (A:P) was lower and the energetic efficiency of the VFA produced was higher in the diet containing sawdust. The addition of urea to the diet with beech sawdust conditioned less effectively, as distinct from the case mentioned above, did not give a clear effect. Urea encouraged the digestibility of pentosanes, glucose and cellulose, but reduced the energetic efficiency of the VFA produced. Xylocel had no clear effect on the digestibility of sugars either. The higher A:P ratio and the lower energetic efficiency of the VFA produced testify to the fact that xylocel in combination with beet molasses was not a sufficient replacer of sugar-beet glycides.     

Effect of feeding pelleted feed on the level of volatile fatty acids in the digestive tract of sheep]

In an experiment with wethers we investigated the effect of complete pelleted feed ration on the concentration of volatile fatty acids in the rumen and intestinal tract. The animals consumed daily 1,300 g of dry matter of a diet which contained 41.81% of meadow hay, 25.28% of barley, 15.37% of sawdust, 14.98% of molasses, 1.32% of urea and 1.24% of a vitamin-mineral supplement for a period of six months. The pelleted diet increased the total amount of volatile fatty acids, the content of propionic acid and especially the content of butyric acid. There appeared a decrease in the ratio of acetate: propionate. On the basis of the greater energy efficiency of the volatile fatty acid production the animals fed pelleted feed showed a better energy balance. A higher VFA concentration was determined also in the large intestine and the cecum, which proves the importance of fermentation porcesses in these organs.     

Effect of ruminal infusion of glucose, volatile fatty acids and hydrochloric acid on mineral metabolism in sheep

Two experiments were conducted to study the effects of alterations in ruminal pH and volatile fatty acid (VFA) concentrations on utilization of Mg and other minerals. In Exp. 1, two metabolism trials were conducted with 12 ruminally cannulated crossbred wethers fed 800 g/d of orchard-grass (Dactylis glomerata, L.) hay. After each feeding, wethers were ruminally infused with 500 ml (4.2 ml/min) or either 1) deionized water, 2) 40% (w/v) glucose solution, 3) .26 M propionic and .17 M butyric acid solution or 4) .35 M HCl. The pH of the VFA solution was adjusted to 6.8 with 10N NaOH. In Exp. 2, a metabolism trial was conducted with 12 ruminally cannulated crossbred wethers fed 600 g of orchard-grass hay and infused with a buffered VFA solution prepared as in Exp. 1 or with an unbuffered solution. In both experiments each trial consisted of a 5-d adaption period followed by four 5-d collections of feed, feces and urine. Compared with the glucose treatment, infusion of the buffered VFA solution produced similar acetic and propionic and higher (P less than .05) butyric acid concentrations (Exp. 1). The HCl solution produced changes in ruminal and pH values similar to those of the glucose infusion. In Exp. 1, apparent absorption of Mg was increased over twofold by the glucose infusion (P less than .05), but the other infusions had no effect. Apparent absorption of P was decreased (P less than .05) by HCl infusion, and K absorption was decreased by HCl and glucose infusions. In Exp. 2, infusion of the unbuffered VFA solution decreased apparent Mg absorption by 15.7%, compared with infusion of the buffered solution. These experiments suggest that the increased Mg absorption observed with carbohydrate supplementation is not due to alterations in ruminal pH or VFA levels.     

Effects of ruminal infusion of volatile fatty acids on plasma concentration of growth hormone and insulin in sheep.

In an initial experiment we observed postprandial changes in plasma concentrations of growth hormone (GH), insulin, glucagon, and somatostatin (SRIF) in sheep. We then examined whether increasing the rumen concentration of volatile fatty acids (VFA) by infusing a VFA mixture at three rates (53.5, 107, and 214 micromol/kg/min for 4 hr) mimicked the postprandial changes in hormone secretion. Feeding significantly (P < 0.05) suppressed the plasma GH concentration for 6 hr, whereas it significantly (P < 0.05) increased plasma concentrations of insulin, glucagon, and SRIF. Plasma glucose levels tended to decrease after feeding but then gradually increased over the prefeeding level (P < 0.05). Intraruminal infusion of the VFA mixture at 107 micromol/kg/min caused similar changes in ruminal VFA concentrations to those seen after feeding. The infusion significantly (P < 0.05) suppressed GH secretion in a dose-dependent manner, whereas it caused a significant (P < 0.05) increase in insulin and glucose concentrations without changing glucagon concentrations. From these results, we conclude that the postprandial change in ruminal VFA concentration may be a physiological signal which modifies GH and insulin secretion in sheep.     

Measurement of volatile fatty acid production rates in sheep given roughage

Measurement of the irreversible loss rate (ILR) of acetate, propionate and butyrate by radioisotope dilution of the respective tracers in sheep offered chopped dried grass from continuous belt type feeders gave 'plateau samples', the specific radioactivity of which had unacceptably high variance (coefficient of variation [cv] of the five or six samples taken from any one animal over the last four hours of 10 hours infusion ranged from 16 to 57 per cent). In an experiment which attempted to identify the source of this variability the distribution of the liquid phase marker 51Cr EDTA into different areas of the rumen was examined during its administration either in liquid form or impregnated on paper. The paper provided better mixing but incurred considerable spillage problems which would be unacceptable where calculations of ILR were required. Radiographic observations were made to examine the mixing of radio-opaque liquid and solid phase markers in the rumen. A better mixing of both was achieved with intermittent than continuous feeding. When 1-14C- and 2-14C-labelled acetate were each infused into the rumen of four sheep given two levels of chopped dried grass by means of hourly feeders, samples of rumen liquor gave much lower variability of the mean plateau specific radioactivity values than was obtained in experiment 1 (cv less than 15 per cent in all but one sheep). The ILRs of acetate and the transfer quotients of carbon from acetate to butyrate obtained using 1-14C- and 2-14C-labelled acetate were similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

挥发性腊肪酸和乳酸的测定方法研究

乙酸、丙酸、丁酸、戊酸、异戊酸等广泛地存在于自然界中．它们的共同特点是具有较强的挥发性．生物学上一般称之为挥发性脂肪酸（Volatile Fatty Acids，VFA）。VFA在动物科学和食品科学上具有十分重要的意义，其代谢和含量是这些研究领域中常遇到的问题。因此，一个好的测定方法是研究中十分必要的．     

挥发性脂肪酸和乳酸的测定方法研究

乙酸、丙酸、丁酸、戊酸、异戊酸等广泛地存在于自然界中,它们的共同特点是具有较强的挥发性,生物学上一般称之为挥发性脂肪酸(Volatile FattyAcids,VFA)。VFA在动物科学和食品科学上具有十分重要的意义,其代谢和含量是这些研究领域中常遇到的问题。因此,一个好的测定方法是研究中十分必要的。挥发性脂肪酸的测定方法有比色法、滴定法、色谱法等。相比之下,气相色谱法以快速、准确、简便,能分别测定各个组分而适用于多种样品(如:青贮饲料、瘤胃液、血液、饮料等)。但是,气相色谱法也受多种条件的影响,如色谱条件、样品的处理方法等。利…     

脂肪酸添加剂对奶牛瘤胃挥发性脂肪酸和甲烷的影响

21头安装瘤胃瘘管的荷斯坦产奶牛随机分为对照组和试验Ⅰ~Ⅵ组,每组3头,对照组饲喂全混日粮(TMR),试验Ⅰ~Ⅵ组每天饲喂TMR加50.0 g、100.0 g、150.0 g、200.0 g、250.0 g、300.0 g/头复合脂肪酸日粮,主要探讨复合脂肪酸对奶牛瘤胃甲烷(CH4)产量、挥发性脂肪酸(VFA)、氨氮(NH3-N)浓度和pH值及产奶性能的影响。结果,TMR中每天添加150.0~200.0 g/头复合脂肪酸,明显(P<0.05)提高奶牛乳脂率和瘤胃乙酸浓度,显著(P<0.05)降低奶牛的CH4释放量、CH4能/GE值和瘤胃NH3-N浓度,对奶牛的标准乳(FCM)、乳干物质、乳蛋白和乳糖均有提高趋势,能有效地提高奶牛的经济效益和生态效益。     

Secretion of endogenous urea into the cecum in sheep

In one-hour intervals before feeding and 1, 2, 3, 4 and 5 hours after feeding, three wethers were studied for the quantitative secretion of urea N and ammonia N into the caecum pouch (volume 80 ml). The amount of ammonia N secreted into the caecum ranged from 10.0 +/- 2.8 to 20.0 +/- 3.5 microM/h. The concentration of ammonia N was 271.2 +/- 60.6 microM/l, on the average. The passage of urea N showed no statistically significant differences before and after feeding (37.8 +/- 4.2 - 41.4 +/- 5.0 microM/h). The concentration of urea N in the caecum pouch was from 617.8 +/- 67.8 microM/l to 710.7 +/- 82.1 microM/l. Urea penetrates through the caecum wall into the caecum mostly in the form of a whole molecule, only its small proportion has the form of ammonia, its hydrolysis product.     

The role of intestinal volatile fatty acids in the Salmonella shedding of pigs

Factors affecting colonization of the intestinal tract by salmonellas were studied in two pig herds. In herd H 18% of the faecal samples taken from live pigs and 30% of the colon content samples collected at slaughter contained salmonellas. In contrast, the 50 faecal samples taken from pigs of herd L were negative and only 2% of the colon contents collected at the yielded salmonellas. An antibacterial effect inhibiting salmonella multiplication was demonstrable in vitro in colon contents from pigs of herd L. No such effect was found to exist in samples taken from pigs of herd H. The antibacterial effect is due to the non-dissociated volatile fatty acid (VFA) molecules present in the colon content. As the degree of VFA dissociation depends on the pH of the environment, at lower pH values (pH 6.1 +/- 0.2) of the colon contents from herd L the ratio of non-dissociated VFA molecules is higher and the resulting antibacterial effect is stronger than in samples from herd H (pH 7.1 +/- 0.3).     

放牧前后肉用羊体脂脂肪酸组成变化的研究

选用100日龄、1岁以及5岁年龄段的杂种肉用羊为实验用羊，采用冷式提取脂肪技术以及气相色谱（GC）技术测定了肉用羊不同阶段体脂脂肪酸的变化。研究结果表明，放牧前与放牧后羊体脂脂肪酸表现出显著的变化。在肌肉中，放牧前羔羊、放牧1岁羊及5岁成年羊之间在单链不饱和脂肪酸含量上有显著的差异（P＜0．05）分别为45．22％、27．46％和24．83％。羔羊和1岁羊及成年羊在多聚不饱和脂肪酸的含量上也有着显著的差异，分别为8．45％、5．78％和5．1％（P＜0．05），奇数碳脂肪酸在5岁成年羊肉中为最高，达到6．09％，其次是1岁羊，为5．74％，羔羊最低，仅为2．89％，三个年龄组之间的差异显著（P＜0．05）。肌肉中短链脂肪酸的含量以羔羊为最低，其含量为0．14％，其次是1岁羊，为0．34％，5岁成年羊的含量最高，达于0．41％。皮下脂肪酸在年龄组之间也表现出变化，三个年龄组之间比较，单链不饱和脂肪酸的含量以羔羊为最高46．35％，其次为1岁羊31．55％，最低是5岁成年羊28．45％，三个年龄组之间差异显著（P＜0．05）。多聚不饱和脂肪酸的含量，1岁羊最高为5．69％，羔羊次之5．47％，5岁成年羊最低4．86％，羔羊和1岁羊该脂肪酸的含量显著高于5岁成年羊（P＜0．0），但是，羔羊和1岁羊之间没有显著差异（P＞0．05）。三个年龄组皮下脂肪中奇数碳肪酸的含量表现出显著的差异（P＜0．05），其含量分别为5．46％、5．84％和5．99％。羔羊皮下脂肪短链脂肪酸的含量为0．1％，显著低于5岁成年羊（0．2％）。1岁羊短链脂肪酸的含量居中为0．14％，与其他两个年龄组没有显著性差异（P＞0．05）。     

Volatile fatty acids in the rumen of sheep fed a synthetic diet

A trial was conducted with wethers to study the effect of the administration of a synthetic diet (composition: 30.125% starch, 30.125% sucrose, 25% cellulose, 5.25% urea, 8.125% mineral supplement, 1.25% maize oil and 0.125% cholinechloride) upon rumen fermentation. The adaptation to the synthetic diet lasted three months, the proportion of the synthetic diet increasing every week (by 10%) to the detriment of a traditional diet (composition: 0.5 kg meadow hay, 0.3 kg barley, 0.2 kg wheat bran, salt and straw ad libitum). In the 10th week the animals consumed 0.5 kg granular synthetic diet, 0.2 kg cellulose flakes and 0.01 kg polystyrene. After three weeks of the administration of the fully synthetic diet, the rumen fluid was sampled after morning feeding in intervals of 0, 1, 3, 5 and 7 hours. In the dynamics of fermentation, statistically significant differences were found only in isobutyric and isovaleric acid between the 0th and 1st and between the 5th and 7th hours (P less than 0.05--P less than 0.001). The data for all the time intervals were recalculated to average values. These were as follows: total volatile fatty acids 63.03 mmol/l, acetic acid 51.00 mol%, propionic acid 26.75 mol%, butyric acid 19.43 mol%, isobutyric acid 0.91 mol%, isovaleric 1.27 mol%, valeric acid 0.62 mol%, energy efficiency of VFA production 78.23%. The obtained data are confronted with literary data on synthetic diets which contained urea and various energy sources.