Urinary aromatic acid excretion by fed and fasted sheep in relation to protein metabolism in the rumen

Metabolisable energy of grass and red clover silages fed to sheep at maintenance level

This study investigated the effect of forage type (grass or red clover) and harvesting time (primary growth or regrowth) of silage on energy and N utilisation by sheep fed at maintenance level. Specifically, the assumption of constant loss of energy of digestible organic matter from energy losses in urine and CH4 applied in evaluation of silage metabolisable energy (ME) was investigated. Urinary excretion of high-energy phenolic compounds related to solubilisation of lignin was assumed to affect urinary energy (UE) losses from sheep fed highly digestible grass silage (GS). A total of 25 primary growth and regrowth silages of timothy (Phleum pratense) and meadow fescue (Festuca pratensis) grass mixtures and red clover (Trifolium pratense) samples collected in digestibility trials with sheep, including faecal and urine samples, were used for energy and N determinations. Urinary concentration of monophenolic compounds and CH4 emissions in vitro were also analysed. Daily faecal N output, CH4 yield (MJ/kg DM intake), proportion of CH4 energy in digestible energy (DE) and proportion of UE in DE were greater (P ≤ 0.03) in sheep fed red clover silage (RCS) than GS. Furthermore, less (P = 0.01) energy was lost as UE of DE in sheep fed primary growth GS compared with the other treatments. The relationship between UE and silage N intake or urinary N output for both silage types (i.e. grass v. red clover) was strong, but the fit of the regressions was better for GS than RCS. The CH4/DE ratio decreased (P < 0.05) and the UE/DE ratio increased (P < 0.05) with increasing organic matter digestibility in RCS. These relationships were not significant (P < 0.05) for the GS diets. The regression coefficient was higher (P < 0.05) for GS than RCS when regressing ME concentration on digestible organic matter. The results of this study imply that ME/DE ratio is not constant across first-cut GS of different maturities. The ME production response may be smaller from highly digestible first-cut GS but could not be clearly related to urinary excretion of monophenols derived from solubilisation of lignin. Furthermore, energy lost in urine was not clearly defined for RCS and was much more predictable for GS from silage N concentration.

Production of tyrosine and other aromatic compounds from phenylalanine by rumen microorganisms

Rumen contents from three fistulated Japanese native goats fed Lucerne hay cubes (Medicago sativa) and concentrate mixture were collected to prepare the suspensions of mixed rumen bacteria (B), mixed protozoa (P) and a combination of the two (BP). Microbial suspensions were anaerobically incubated at 39 degrees C for 12 h with or without 1 mM of L-phenylalanine (Phe). Phe, tyrosine (Tyr) and other related compounds in both supernatant and microbial hydrolysates of the incubations were analyzed by HPLC. Tyr can be produced from Phe not only by rumen bacteria but also by rumen protozoa. The production of Tyr during 12 h incubation in B (183.6 mumol/g MN) was 4.3 times higher than that in P. One of the intermediate products between Phe and Tyr seems to be p-hydroxyphenylacetic acid. The rate of the net degradation of Phe incubation in B (76.0 mumol/g MN/h) was 2.4 times higher than in P. In the case of all rumen microorganisms, degraded Phe was mainly (> 53%) converted into phenylacetic acid. The production of benzoic acid was higher in P than in B suspensions. Small amount of phenylpyruvic acid was produced from Phe by both rumen bacteria and protozoa, but phenylpropionic acid and phenyllactic acid were produced only by rumen bacteria.

Quantitative determination of aromatic amino acids and related compounds in rumen fluid by high-performance liquid chromatography

A rapid method for the quantitative determination of tyrosine (Tyr), phenylalanine (Phe), p-hydroxybenzoic acid (HBA), p-hydroxyphenylacetic acid (HPA), benzoic acid (BZA), p-hydroxyphenylpyruvic acid (HPY), phenylacetic acid (PAA), phenyllactic acid (PLA), tryptophan (Trp), indoleacetic acid (IAA), phenylpyruvic acid (PPY), phenylpropionic acid (PPA) and cinnamic acid (CNA) in goat rumen fluid was established by high-performance liquid chromatography (HPLC). The mobile phase used for isocratic elution was 50 mM sodium phosphate buffer (pH 6.5)-methanol (97:3, v/v). The flow-rate was 1.0 ml/min; column temperature 40 degrees C and compounds were monitored at 215 nm with a UV absorbance detector after injection of 10 microl of filtered rumen fluid. Analysis was completed within 40 min. The minimum detectable limits of quantification (microM) of these compounds were Tyr, 2; Phe, 3; HBA, 1; HPA, 2; BZA, 2; HPY, 8; PAA, 3; PLA, 4; Trp, 2; IAA, 2; PPY, 15; PPA, 8 and CNA, 4. Detectable levels of Tyr, Phe, HPA, BZA, HPY, PAA, PLA, Trp and PPA were found in the deproteinized rumen fluid of goat fed a haycube and concentrate mixture. PAA was the predominant compound before and after feeding. The concentrations of HPA, BZA, PAA, PLA and PPA in the goat rumen fluid increased after feeding, while the concentration of Tyr decreased. Phe, HPY and Trp were minor components at all times. PPY, IAA and CNA were not detected and HBA was not completely resolved in the goat rumen fluid.

Excretion of benzoic acid derivatives in urine of sheep given intraruminal infusions of 3-phenylpropionic and cyclohexanecarboxylic acids

The quantitative relationship between the urinary excretion of benzoic acid (BA) and the uptake of 3-phenylpropionic (PPA) and cyclohexanecarboxylic (CHCA) acids was assessed. PPA and CHCA are produced in the rumen by microbial fermentation of lignocellulosic feeds and metabolized, after absorption, to BA which is excreted in the urine mainly as its glycine conjugate hippuric acid (HA). Four sheep nourished by intragastric infusions of all nutrients were given continuous ruminal infusions of PPA (8, 16 or 24 mmol/d) either alone or with CHCA (8 or 16 mmol/d) in a factorial experiment. The treatments were allocated to ten consecutive 6 d periods, with a control being repeated at periods 1, 5 and 10. PPA and CHCA ruminal absorption rates, estimated using the liquid-phase marker Cr-EDTA, were 0.78 (SD 0.29)/h and 0.88 (SD 0.28)/h respectively. For the control, HA excretion was only 0.22 (SD 0.33) mmol/d and free BA was absent. For the other treatments, both HA and free BA were present and HA accounted for 0.85 (SD 0.05) of total BA: The urinary excretion of total BA showed a significant linear correlation (r = 0.997, P < 0.001) with the amounts of PPA and CHCA infused. The urinary recovery of infused PPA and CHCA as total BA was 0.79 (SE 0.01). Faecal excretion of BA and its precursors was negligible. Results of this study show that urinary total BA is a potential estimator of the absorption of PPA + CHCA produced in the rumen.

Determination of aromatic metabolites in ruminant urine by high-performance liquid chromatography

A method based on reversed-phase HPLC is reported for the separation and quantification of various urinary aromatic metabolites: hippuric, phenylaceturic, salicyluric, benzoic, phenylacetic, salicylic, 3-phenylpropionic and cinnamic acids and several phenols in ruminant urine. In this method, a Nova-Pak C18 (4 microns) 150 x 3.9 mm I.D. column, two solvents [A: 15% methanol in 20 mM acetic acid (pH 3.3); B: methanol) in a gradient mode at a flow-rate of 0.8 ml/min, and UV detection at 210 nm were used. Quantification of the total (free and conjugated) benzoic, phenylacetic and salicylic acids present in urine was achieved by hydrolysis of the samples in 3 M HCl at 100 degrees C for 24 h prior to HPLC analysis. The lowest detection concentration was 50 mumol/l. This method is useful for scanning the profile of aromatic metabolites in urine of ruminants, which provides information on the diets the animals receive.

Rapid determination of phenylalanine and its related compounds in rumen fluid by high-performance liquid chromatography

A rapid method for the determination of phenylalanine (Phe), tyrosine (Tyr), benzoic acid (BZA), phenylacetic acid (PAA), phenyllactic acid (PLA), phenylpyruvic acid (PPY), phenylpropionic acid (PPR), and cinnamic acid (CNM) in goat rumen fluid was established by high-performance liquid chromatography (HPLC). The mobile phase used for isocratic elution was methanol-sodium acetate buffer (pH 6.5) (8:92, v/v). The compounds were monitored at 220 nm with a UV detector. A 5-microliters portion of the filtrated rumen fluid was analyzed and the analysis was completed within 20 min. The minimum detectable limits (microM) of these compounds were: 12 for Phe, 3 for Tyr, 3 for BZA, 9 for PAA, 12 for PLA, 15 for PPY, 20 for PPR, and 8 for CNM. The average contents of Phe, BZA, PAA, PLA, and PPR in the rumen fluid of three goats were 15.4, 73.7, 615.9, 51.1, and 39.9 microM before morning feeding, 17.0, 123.7, 650.4, 208.2, and 502.4 microM at 3 h after feeding, and 18.4, 124.2, 510.0, 129.9, and 178.5 microM at 6 h after feeding, respectively. Of these compounds PAA was present at the highest concentration both before and after feeding. The content of PPR extremely increased especially at 3 h after feeding. The other three compounds, i.e. Tyr, PPY, and CNM, were not detected in goat rumen fluid.

Lignocellulose degradation and subsequent metabolism of lignin fermentation products by the desert black Bedouin goat fed on wheat straw as a single-component diet

Bedouin goats were fed on wheat straw as a single-component diet under two watering regimens, drinking once daily or once every 4 d, in order to clarify whether lignin-degradation products were absorbed, metabolized and excreted in urine. Acid-soluble lignin accounted for 220 g/kg total lignin, its digestibility was the highest (0.87) and was unaffected by water deprivation. Acid-insoluble lignin accounted for 780 g/kg total lignin and its digestibility increased during water deprivation from 0.21 to 0.41. Alkali-soluble lignin accounted for 320 g/kg total lignin and its digestibility increased during water deprivation from 0.44 to 0.53. Digestibility of structural carbohydrate was considerably higher than that observed in other domesticated ruminants fed on wheat straw. It responded positively to water deprivation, increasing from 0.63 to 0.73 with cellulose and from 0.61 to 0.68 with hemicellulose. The amount of urinary aromatic acids, mainly in the form of hippuric acid, considerably exceeded the potential contribution of any non-lignin component which might affect the excretion of aromatic acids. A considerable percentage (71-76) of the apparently digested lignin was not accounted for as soluble phenolic compounds in faeces or as aromatic acids in urine, and hence was apparently completely metabolized. Lignin is a key substrate which is extensively digested in goats fed on low-quality forage, with subsequent absorption of endproducts. This enhanced the availability of structural carbohydrates for fermentation and was associated with excretion of high-energy metabolites in the form of benzoic and hippuric acids.

The origin of urinary aromatic compounds excreted by ruminants. 4. The potential use of urine aromatic acid and phenol outputs as a measure of voluntary food intake

1. Studies were made of the extent to which p-cresol, catechol, quinol and orcinol infused through rumen or abomasal cannulas to sheep were recovered in their urine. 2. Rumen fermentation of dietary phenolic compounds caused the excretion of simple phenols in the urine. In decreasing order of magnitude these were: p-cresol, catechol, phenol and 4-methylcatechol with only traces of quinol and orcinol. 3. The percentages of rumen-infused p-cresol or orcinol recovered as increments in the urinary phenol outputs of sheep (94 and 99% respectively) following infusion showed that rumen degradation of these phenols was negligible. 4. After rumen infusion of catechol and quinol, mean recoveries of these phenols in urine were only 55 and 77% respectively. Possible reasons for these incomplete recoveries are discussed. 5. Studies were also made of the use of the urinary phenol output of phenols characteristics of particular forages as indices of their voluntary intake by sheep. Calluna vulgaris L. (Hull) (heather) may contain 1300-3600 mg/kg dry matter (DM) of orcinol and 200-800 mg/kg DM of quinol as beta-glycosides. When heather was offered ad lib. to sheep given one of five levels of grass, linear relationships were found between heather intake and urinary quinol and orcinol outputs. 6. The urinary output of aromatic acids was also determined when sheep ate grass and heather. Urinary phenylacetic acid output was linearly related to grass but not to heather intake. The relationship between urinary phenylacetic acid output and grass intake could vary with different forages but that between orcinol output and heather intake was considered a useful index of heather intake. 7. Methods for the assay of urine phenols are discussed.

The origin of urinary aromatic compounds excreted by ruminants. 3. The metabolism of phenolic compounds to simple phenols

Dietary phenolic cinnamic acids are hydrogenated in the side-chain, demethylated and dehydroxylated in the rumen and are responsible for the large urinary output of benzoic acid by ruminants. 2. Decarboxylation of phenolic acids to simple phenols is another reaction of the intestinal microflora and experiments were made to determine the extent of this reaction in the rumen of sheep. 3. In five experiments phenolic compounds, quinic acid or casein were infused into the rumen or abomasum of sheep and increments in urinary outputs of phenolic acids and phenols determined by thin-layer and gas-liquid chromatography. 4. Production of phenols was almost exclusively confined to reactions in the rumen. 5. Rumen administration of phenolic benzoic or phenylacetic acids which contained a 4-hydroxy substituent yielded large increments in urinary phenol outputs. Other phenolic benzoic and phenylacetic acids were not decarboxylated. Rumen decarboxylation of 4-hydroxy-3-phenylpropionic acid did not occur and decarboxylation of 4-hydroxycinnamic acids was slight. 6. Nearly half the tyrosine content of rumen-administered casein was excreted as p-cresol, a decarboxylation product of 4-hydroxyphenylacetic acid, p-Cresol was the principal phenol found in sheep urine. 7. Catechol and phenol were consistently found in sheep urine samples and p-ethylphenol, resorcinol, quinol, 4-methylcatechol, orcinol and pyrogallol were also found when suitable precursors were infused to the rumen. 8. It is concluded that p-cresol is a rumen metabolite of tyrosine. The other phenols found are microbial metabolites of phenolic precursors which are either widely distributed in plants such as 4-hydroxybenzoic, protocatechuic and vanillic acids or of more limited distribution such as the orcinol glycosides of some Ericaceous plants.

The origin of urinary aromatic compounds excreted by ruminants. 1. The metabolism of quinic, cyclohexanecarboxylic and non-phenolic aromatic acids to benzoic acid

1. The contribution of dietary constituents to the large urinary output of benzoic acid characteristic of ruminants and some herbivores is not well understood. 2. Methods for the analysis of quinic, cyclohexanecarboxylic, benzoic, phenylacetic, 3-phenylpropionic and cinnamic acids in urine and in rumen fluids were developed. 3. The urinary output of aromatic acids by sheep given seven-rations was determined: benzoic acid output varied between 2.8 and 7.8 g/d; phenylacetic acid output between 0.16 and 1.3 g/d; cinnamic acid between 0.08 and 0.25 g/d and small amounts of 3-phenylpropionic acid were found in some samples. 4. Increments in urinary aromatic acid excretion were determined when the acids listed in paragraph 2 were infused via rumen or abomasal cannulas. 5. When cyclohexanecarboxylic acid was infused 40% of the dose was excreted as urinary benzoic acid after either route of infusion. Quinic acid was completely metabolized in the rumen; following rumen infusion between 16 and 53% of the infused acid was recovered as urinary benzoic acid; none was so recovered after abomasal infusion. 6. Urinary recoveries of rumen- and abomasally-infused aromatic acids were: benzoic acid 90 and 88% respectively as benzoic acid, phenylacetic acid 78 and 83% respectively as phenylacetic acid, 3-phenylpropionic acid 96 and 105% respectively as benzoic acid and cinnamic acid, 70 and 70% respectively as benzoic acid. 7. The concentration of aromatic acids in rumen fluid varied with time after feeding: cyclohexanecarboxylic acid was maximal (7 mg/l) 1 h after feeding, benzoic acid was always a minor component (0.5 +/- 0.5 mg/l), phenylacetic acid varied between 0 and 35 mg/l and 3-phenylpropionic acid between 25 and 47 mg/l. Cinnamic acid was not found in rumen fluid but on rumen infusion of this acid the concentration of 3-phenylpropionic acid in rumen fluid increased by 10 mg/l rumen fluid per g infused per d. 8. The incomplete metabolism of quinic and cyclohexanecarboxylic acids to urinary benzoic acid is discussed. It is concluded that the principal dietary precursors of urinary benzoic acid in ruminants are compounds yielding 3-phenylpropionic acid on microbial fermentation in the rumen. The small amount of cinnamic acid characteristic of ruminant urine arises as an intermediate in the beta-oxidation of 3-phenylpropionic acid in the body tissues.

The origin of urinary aromatic compounds excreted by ruminants. 2. The metabolism of phenolic cinnamic acids to benzoic acid

1. The extent to which phenolic derivatives of benzoic acid (seven); of phenylacetic acid (one); of 3-phenylpropionic acid (one) and of cinnamic acid (six) served as precursors of the urinary benzoic acid excreted by sheep was determined after administration as continuous drips via rumen or abomasal cannulas. 2. Phenolic derivatives of benzoic or of phenylacetic acid were not dehydroxylated to yield aromatic acids following administration via either route. 3. Rumen infusion of phenolic derivatives of both 3-phenylpropionic and cinnamic acids gave enhanced rumen concentrations of 3-phenylpropionic acid with negligible amounts of benzoic acid. Between 63 and 106% of the 2-, 3- or 4-hydroxy acids, of the 3,4-dihydroxy acids or of the 3-methoxy, 4-hydroxy acids infused were excreted in the urine as benzoic acid and a variable proportion, characteristic of the individual animal, of up to 20% of the dose as cinnamic acid. 4. Abomasal infusion of monohydroxy 3-phenylpropionic and cinnamic acids did not yield urinary benzoic acid increments. However, between 11 and 34% of abomasally-infused disubstituted phenolic cinnamic acids infused were excreted in the urine as benzoic acid due, it is postulated, to entero-hepatic circulation and microbial metabolism of the infused acids in the large intestine. 5. It is concluded that rumen microbial metabolism of dietary phenolic cinnamic acids to 3-phenylpropionic acid followed by its absorption and oxidation in the body tissues is responsible for the greater part of the benzoic and cinnamic acids found in ruminant urine.