Plasma Volatile Fatty Acids Research Articles

Effects of steam-treated rice straw feeding on growth, digestibility, and plasma volatile fatty acids of goats under different housing systems.

In order to use rice straw as forage in livestock feeding, the effects of steam-treated rice straw (at 15.5 kgf/cm(2) for 120 s) feeding on growth performance, plasma volatile fatty acid profile, and nutrient digestibility of goats were determined. Twenty male goats (18.69 ± 0.34 kg) were used in an 84-day trial. The goats were divided into four groups of five goats each to receive steam-treated (STRS) or untreated (UTRS) rice straw diet under closed house (CH) and open house (OH) systems. The results revealed that the goats fed with STRS had significantly higher dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) digestibility; similarly, the average daily weight gain and feed conversion ratio were higher for STRS groups under both CH and OH systems than those for UTRS. The plasma protein and insulin in STRS and cholesterol in UTRS groups was higher (P < 0.05) at 60 days but found not different (P > 0.05) at 30 days. The plasma amylase, lipase, T3, T4 and glucagon at 30 and 60 days were not different (P > 0.05) among the groups. The plasma acetate, propionate, butyrate, and total volatile fatty acid were higher (P < 0.05) in STRS groups at 30 and 60 days. The housing conditions had no effects (P > 0.05) on these parameters. It could be concluded that steam treatment of rice straw at 15.5 kgf/cm(2) for 120 s increased apparent nutrient digestibility, hence increased the growth and feed efficiency of growing goats.

Fibre digestibility, abundance of faecal bacteria and plasma acetate concentrations in overweight adult mares.

The purpose of the present study was to compare digestibility of grass hay, faecal and plasma volatile fatty acid (VFA) concentrations, and faecal bacterial abundance in overweight and moderate-condition mares. Five overweight adult mixed-breed mares and five adult mixed-breed mares in moderate condition were housed individually and limit-fed orchard grass (Dactylis glomerata) hay at 20g/kg body weight (as fed) daily for 14 d. Forage DM and fibre digestibility were determined using AOAC methods; digestible energy was measured using bomb calorimetry; plasma and faecal VFA concentrations were determined by use of GC and MS; faecal Firmicutes, Bacteroidetes, Fibrobacter succinogenes, Ruminococcus flavefaciens and total bacteria abundance was determined by quantitative real-time PCR using previously designed phylum-specific 16S ribosomal RNA gene primers. No differences in hay digestibility, faecal VFA concentrations or faecal bacterial abundance were detected between overweight and moderate-condition mares. Mean plasma acetate concentrations were higher (P=0·03) in overweight (1·55 (range 1·43-1·65) mmol/l) v. moderate-condition (1·39 (range 1·22-1·47) mmol/l) mares. We conclude that the higher plasma acetate in overweight mares should be further investigated as a potential link between gut microbes and obesity in horses.

Effect of Milk Allowance on Concentrate Intake, Ruminal Environment, and Ruminal Development in Milk-Fed Holstein Calves

The aim of the present experiment was to test the hypothesis that a barley-based concentrate would induce an acidic ruminal environment in young calves and that increased milk allowance would alleviate this condition. Eight Holstein calves ruminally cannulated at d 7±1 of age were used to study the effect of variation in barley-based starter concentrate intake induced by 4 different milk allowances (3.10, 4.84, 6.60, and 8.34kg of milk replacer/d; 123g of dry matter/kg of milk) on the ruminal environment, blood variables, and fore-stomach development from wk 2 to 5 of age. Twelve ruminal fluid samples were collected during a weekly 24-h sampling in 4 consecutive weeks. Blood samples were collected by venipuncture between 1200 and 1300h on ruminal sampling days. Rumen papillae development and visceral organ mass were recorded at slaughter. A linear treatment×week effect was observed for concentrate intake, with the calves fed the lowest milk allowance having the fastest increase in concentrate intake whereby these calves reached the same ME intake in wk 5 compared with calves with the highest milk allowance. Effects on ruminal variables were dominated by week of sampling, with minor differences among treatments. Ruminal pH was below 5.5 for 5 to 13 h/d and all calves with concentrate intake above 20g of dry matter/d were observed to have a daily ruminal pH minimum at pH 5.5 or lower. The ruminal concentration of total volatile fatty acids (VFA) increased from 71 to 133±9 mmol/L in wk 2 to 5 and was characterized by a relatively high molar proportion of propionate, increasing from 34 to 40 mol/100mol of VFA in wk 2 to 5. In addition, the presence of ethanol and propanol as well as numerous VFA esters points to a ruminal environment with a relatively high hydrogen pressure. Plasma glucose and insulin responded to the highest milk allowance in wk 2 to 4. Plasma VFA and ketone bodies increased with the lowest milk allowance in wk 4 to 5. At slaughter, empty wet weights of the rumen + reticulum and omasum as well as mass of digesta in these compartments were found to decrease linearly and perirenal fat was found to increase linearly with milk allowance, indicating that the milk allowance changed the body composition of the calves. Lengths of ruminal papillae in the atrium and ventral ruminal sac were not affected by treatment. We concluded that the ruminal environment of young calves fed a barley-based starter concentrate was characterized by a low ruminal pH and high VFA concentration regardless of the milk allowance.

Effects of solvent extraction on the hypocholesterolaemic action of oat bran in the rat.

In adult male rats fed on a cholesterol-free synthetic diet, plasma cholesterol concentrations were lowest with oat bran, intermediate with cellulose and highest with wheat bran. Plasma triacylglycerols (TAG) were similar with wheat bran and cellulose but higher with oat bran. The concentrations and pools of caecal volatile fatty acids (VFA) were lowest with cellulose and equally higher with oat bran and wheat bran. Plasma VFA concentrations in the hepatic portal vein reflected those in caecal digesta and were unrelated to plasma cholesterol. Feeding oat bran after extraction with n-pentane gave plasma cholesterol concentrations similar to that found with wheat bran. Reconstitution of oat bran with extracted lipids did not restore the cholesterol-lowering effect. Addition of the extracted material to a wheat-bran diet had no effect on plasma cholesterol. Plasma TAG were higher with the oat bran and reconstituted-oat-bran diets than with wheat-bran or cellulose diets. However, extracted oat bran + safflower oil gave similar TAG concentrations to that with wheat bran. These extractions and additions did not change caecal bile acid or neutral sterol concentrations. Effects of these diets on plasma cholesterol were unrelated to their tocotrienol or tocopherol content. Addition of n-pentane to oat bran followed by evaporation of solvent gave plasma cholesterol concentrations that were significantly higher than untreated oat bran but lower than similarly treated wheat bran. It is concluded that oat bran affects cholesterol metabolism through a pentane-soluble component as well as non-starch polysaccharides. It appears that the activity of this lipid is not transferable by simple addition of the solvent extract to the whole diet.

Changes in Plasma Volatile Fatty Acids in Response to Weaning and Feed Intake in Young Calves

Effects of weaning age on plasma VFA were examined using 16 Holstein heifer calves. Animals entered the study at 6±3.5 d of age and were fed 1.8kg milk twice daily to 28 (early weaning) or 56 d (late weaning) and a commercial pelleted calf starter from 0 (early) or 28 (late) d. Blood was sampled once weekly for 14 wk Total blood concentrations of VFA, acetate, propionate, and butyrate were higher in calves weaned early. Difference between treatments was greatest during wk 5 to 8, after early calves had been weaned. Total VFA and acetate were both highly correlated with grain intake (r = .77), whereas propionate (r = .47) and butyrate (r = .56) were less highly correlated. Data indicate that blood VFA responded rapidly to dry feed intake, and adaptation to high grain diets was complete by 1 to 2wk postweaning.

Effects of Food Restriction and Starvation-Refeeding on Volatile Fatty Acid Concentrations in the Rat

Adult male rats were fed either ad libitum or at levels of 19 or 15 g of nonpurified diet per rat daily or subjected to 48 h of starvation followed by 24 h of refeeding. Concentrations of total and individual volatile fatty acids (VFA) in cecal contents were higher in rats fed ad libitum than in those restricted to 19 or 15 g/d. Only butyrate concentration was lower in rats given 15 g/d than in those given 19 g/d. In starved animals all cecal VFA declined within 24 h of food removal, but the greatest change was in butyrate, which fell to less than 12% of the initial value. Acetate and propionate fell further after 48 h, but their concentrations were restored to control values within 24 h of refeeding while butyrate remained depressed by 50%. Cecal pH was closely related to total VFA concentration, although the highest degree of correlation was with butyrate. Hepatic portal venous plasma VFA concentrations generally reflected those in cecal digesta except that the proportion of butyrate was relatively lower in this blood vessel than in cecal contents. Under all conditions acetate was the only VFA found in arterial plasma and in the fully fed state was lower than in hepatic portal venous plasma. Food restriction and starvation did not alter arterial concentrations, indicating abolition of net uptake. We conclude that all VFA are affected by availability of fermentable material to the large bowel microflora but that the disproportionate changes in butyrate may reflect preferential use of this acid by cells of the large bowel wall.

Effects of dietary oat bran on faecal steroid excretion, plasma volatile fatty acids and lipid synthesis in rats

Two mechanisms have been proposed for the hypocholesterolaemic effects of dietary oat bran, i.e. acceleration of cholesterol catabolism or inhibition of cholesterol biosynthesis. The latter is proposed to occur via propionate formed through large bowel microbial fermentation of fibre. We have examined both of these mechanisms in rats fed dietary oat bran and have found that faecal bile acid and neutral sterol excretion was enhanced compared with animals fed cellulose. In contrast, concentrations of propionate in the hepatic portal vein, although raised by dietary oat bran, were less than 2% of those at which inhibition of hepatic cholesterogenesis has been observed in vitro. When hepatic cholesterol synthesis was measured with 3H 2O, it was increased in oat branfed rats. Therefore, it appears most likely that the hypocholesterolaemic effects of this cereal fibre preparation can be explained by increased faecal steroid excretion and not through inhibition of cholesterogenesis by volatile fatty acids of large bowel origin.

Effects of wheat bran and porridge oats on hepatic portal venous volatile fatty acids in the pig.

Adult male pigs (40-60 kg of body weight) of the Kangaroo Island strain were surgically implanted with chronic indwelling hepatic portal venous cannulae. After a 24-hour fast the animals were given meals containing 500 g of either wheat bran or porridge oats and 200 g of sucrose and 2 litres of milk. With both cereal preparations plasma volatile fatty acids rose in the hepatic portal vein but the increase was significantly greater with wheat bran. Omission of sucrose and milk did not alter the response to porridge oats but diminished the response to wheat bran. These changes in plasma volatile fatty acids were unaffected by prior cooking of the cereals with hot water. With all test meals acetate and propionate were the major acids found, with butyrate contributing less than 8% of the total. This compositional profile was also found when the pigs were fed a commercial ration. The absence of butyrate differed from observations in the rat and reflected low concentrations of this acid in large bowel digesta. The difference in the response of the concentration of volatile fatty acids to feeding porridge oats and wheat bran in the pig was also the reverse of that found in the rat. These species differences may be of significance in relation to the choice of animal models for human fibre metabolism.

Plasma and caecal volatile fatty acids in male and female rats: Effects of dietary gum arabic and cellulose

Adult male and female rats were fed synthetic diets containing 10% gum arabic or cellulose. Concentrations of total volatile fatty acids in caecal fluid and hepatic portal venous plasma of both sexes were higher on the gum arabic diet. Total and individual acids in caecal fluid did not differ between male and female rats fed gum arabic, but with cellulose concentrations of acetate and propionate were significantly lower in females than in males. Caecal pH correlated negatively with volatile fatty acid concentration in both sexes, but with gum arabic, pH was significantly lower in males than in females with the same caecal volatile fatty acid concentration. The concentration and distribution of plasma volatile fatty acids in the hepatic portal vein generally reflected that of caecal fluid although acetate concentrations were lower in male than in female rats fed gum arabic. Blood glucose and plasma triacylglycerols were unrelated to hepatic portal venous plasma volatile fatty acids but in males liver glycogen in each dietary group was positively correlated with volatile fatty acid concentration. This relationship was absent in females. It is concluded that there are differences in the production and absorption of volatile fatty acids between male and female rats and that these are affected by the source of dietary fibre.

Comportement alimentaire, rumination, fermentations réticulo-ruminales et acides gras volatils plasmatiques, comparés chez la chèvre et le mouton ; influence du régime

Two-year old Alpine she-goats (n = 3) and Texel ewes (n = 3) were compared as to eating behaviour, rumination and volatile fatty acids (VFA) in rumen and blood. The animals were fed once daily with two different proportions (20 and 80%) of barley and hay. Dry matter intake was fixed at 48 g D.M/kg P0.75 per day. In similar feeding and environmental conditions, eating behaviour and rumination of goats and sheep did not differ much: the goats tended to eat faster and there were more rumination periods in the sheep. Latency time, mean duration of rumination periods, daily rumination time and circadian pattern of rumination did not differ significantly between the two species (fig. 1). With both diets we observed a higher VFA concentration and a lower acetate/propionate ratio in the rumen of the ewes; however, rumen pH was lower only in those eating the 80% barley ration (fig. 2). Blood VFA in the jugular vein did not differ between sheep and goats (fig. 3). The proportion of cereals and hay in the diets affected rumen fermentation and rumination pattern in both species. With a higher concentrate/roughage ratio, rumen and plasma VFA increased, while the pH and acetate/propionate ratio in the lumen juice, the number of rumination periods and daily rumination time decreased. When the animals were fed the 80% barley ration, there was practically no rumination in the first 9 h after the single meal. During this time, rumen pH was minimal and VFA levels in the rumen and blood were maximal.

The effects of acute cold exposure and feeding on volatile fatty acid metabolism in the hind leg of the young ox.

1. Young steers were fed either 20 or 4 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (total VO2), respiratory quotient (RQ) and hind-leg blood flow (leg Q) and oxygen uptake (leg VO2). The arteriovenous difference in plasma concentrations of individual volatile fatty acids (VFA) across the leg was also measured. Net exchange and fractional uptake of VFA by the leg were calculated from these results.2. Cold exposure doubled total VO2, significantly decreased the RQ and caused 3-fold and 10-fold increases in leg Q and leg VO2 respectively in both 4 h- and 20 h-fed steers. Arterial plasma concentrations of total VFA (which was more than 95 % acetate) and net leg uptake of VFA also significantly increased in both groups. Cold had no effect on the fractional uptake of VFA by the leg.3. Feeding shortly before the experiment caused a significant increase in total VO2 in thermoneutrality only, and in RQ, arterial plasma VFA and net VFA uptake by the leg in both environments. There was a significant decrease in the fractional uptake of VFA by the leg.4. Calculations suggest that although circulating acetate could, in theory, supply over 60 % of the energy required by the hind leg in the resting, fed animal, less than 30 % of the increased requirement of the shivering leg could be supplied by acetate during acute cold exposure, even shortly after feeding.

Determination of volatile fatty acids in plasma after ethanolic extraction.

1. A new rapid micro-method for measuring plasma volatile fatty acids is described. The volatile fatty acids are extracted from plasma with ethanol in the presence of a known quantity of internal standard (sodium isobutyrate). After evaporation of the ethanolic solution of the sodium salts, the residue is dissolved in a dilute solution of orthophosphoric acid to permit analysis by g.l.c. 2. A technique of g.l.c. analysis is described which permits the separation of all the volatile fatty acids from the other plasma constituents at temperatures below 100 degrees C in 5 min. 3. Steam-distillation techniques are unsatisfactory when the acetic acid concentrations in the plasma are below 0.2mm. Heating of a number of plasma constituents in acid conditions gives rise to acetic acid. 4. The binding of volatile fatty acids to plasma proteins was studied; this binding is negligible for acetic acid, but increases with the length of the fatty acid carbon chain. 5. The limits of use of the method and the physiological implications are discussed.

Relationship between Postprandial Plasma Volatile Fatty Acids, Glucose and Insulin Levels in Sheep Fed Different Feeds

Relationship between Postprandial Plasma Volatile Fatty Acids, Glucose and Insulin Levels in Sheep Fed Different Feeds

Improved Method for the Determination of Volatile Fatty Acids in Ruminant Blood Plasma

A method is described for blood plasma volatile fatty acids using direct steam distillation with an anti-foaming agent. Free fatty acids are collected on a microcondenser prior to gas liquid chromatographic analysis. The method is accurate through a wide range for acetate (.05 to 2.50 μmoles per liter), propionate, isobutyrate, butyrate, and valerate (5.0 to 220.0μmoles per liter). However, with increasing concentration there is decreasing precision. The low precision at high concentrations is not serious, since precision is good within the physiologic range. Volatile fatty acids from aqueous solutions and those added to sheep and cattle blood plasma were quantitatively recovered. A comparison was made of the volatile fatty acid in the jugular blood of sheep under conditions of fasting and refeeding.

Rumen development in the calf. 2. The effect of diets containing different proportions of concentrates to hay on digestive efficiency.

1. Twenty-four Ayrshire bull calves were reared on either high-concentrate or high-roughage diets to study the effect of diet on the subsequent ability of the calf to digest either concentrates or hay when given alone. The rearing diets were known to produce different types of rumen development. 2. Although there were significant differences between the apparent digestibility coefficients of the high-concentrate and high-roughage rearing diets and between concentrates and hay when given alone, the subsequent ability of the calf to digest either concentrates or hay was unaffected by the type of diet given during the rearing period to 13 weeks of age. 3. The amount of nitrogen retained was significantly greater in calves reared on the high-concentrate diet than in those given the high-roughage diet, but similar amounts of N were retained/100 g gain in body-weight in both groups. After the change in diet, the amount of N retained was significantly greater in calves given concentrates after a rearing diet high in concentrates than in those given concentrates after a rearing diet high in roughage, although in both groups 32% of the N intake was retained. Four of the six calves given hay after a rearing diet high in concentrates were in negative N balance, but only one calf lost weight. Only 19% of the N intake was retained in calves given hay after being reared on a high-roughage diet. 4. The concentration of total volatile fatty acids (VFA) in the rumen contents rose to reach peak levels at about 3 h after food was offered; the concentration then declined. VFA concentrations tended to be higher in calves given the rearing diet high in concentrates than in those given the one high in roughage, and differences reached significance when the diet was changed to one of all concentrates or all hay, with no obvious carry-over effect of the rearing diet. The proportion of propionic, butyric and higher acids tended to be greater in calves given high levels of concentrates than in those given high levels of hay and also tended to rise, irrespective of diet, as the concentration of total VFA rose. 5. A change of diet at 14 weeks from one high in concentrates to one consisting entirely of hay resulted in a significant decline in the viable counts of streptococci, lactobacilli and coliform organisms in the rumen liquor at 16 weeks. The numbers of bacteria were unaffected by the other dietary changes. 6. The concentration of total VFA in plasma of peripheral blood tended to be higher in calves given the high-roughage or all-hay diets. A fall in the concentration of plasma VFA occurred when calves were changed from a high-roughage diet to an all-concentrate diet and a rise in concentration was observed when an all-hay diet replaced one containing a high proportion of concentrates. 7. During the initial rearing period the mean blood plasma glucose concentration was 92.8 mg/100 ml in calves given the high-concentrate diet, a value significantly higher than the mean value of 64.5 mg/100 ml found in calves given the high-roughage diet. The concentra- tion of plasma glucose rose to 89.8 mg/100 ml in calves changed from the high-roughage diet to concentrates and declined to 81.7 mg/100 ml in calves that were given hay in place of the high-concentrate diet. 8. The weight of contents of the reticulo-nunen and omasum and the volume displacement of these organs were significantly greater in calves given hay as the sole diet during the last 3 weeks of life than in those given concentrates during this period. The weight of tissue forming the reticulo-rumen was significantly greater in calves given the all- concentrate diet during the last 3 weeks of life than in those given only hay during this period. It was apparent that the rumen papillas developed rapidly in those calves given concentrates as the sole diet for a period of 3 weeks after a rearing diet high in roughage, whereas there was a marked retrogression of papillas when concentrates were withdrawn from the diet. 9. It is concluded that the ruminant calf adapts readily to marked dietary changes, with the result that differences in the size and structure of the ruminant stomach, which have been shown to occur when different types of diet are given, have no permanent effect on the ability of the calf to digest diets of concentrates or hay.