The simultaneous use of ribonucleic acid, 35S, 2,6-diaminopimelic acid and 2-aminoethylphosphonic acid as markers of microbial nitrogen entering the duodenum of sheep

Amino acid pattern of rumen microorganisms in cattle fed mixed diets-An update

Rumen microorganisms turn small N-containing compounds into amino acids (AA) and contribute considerably to the supply of AA absorbed from the small intestine. Previous studies summarized the literature on microbial AA patterns, most recently in 2017 (Sok et al. Journal of Dairy Science, 100, 5241-5249). The present study intended to identify the microbial AA pattern typical when feeding Central European diets and a maximum proportion of concentrate (PCO; dry matter (DM) basis) of 0.60. Data sets were created from the literature for liquid (LAB)- and particle (PAB)-associated bacteria, total bacteria and protozoa, including 16, 9, 27 and 8 studies and 36, 21, 60 and 18 diets respectively. Because the only differences detected between LAB and PAB were slightly higher Phe and lower Thr percentages in PAB (p < 0.05), results for bacteria were pooled. A further data set evaluated AA-N (AAN) as a proportion of total N in microbial fractions and a final data set estimated protozoal contributions to total microbial N (TMN) flow to the duodenum, which were used to calculate weighted TMN AA patterns. Protozoa showed higher Lys, Asp, Glu, Ile and Phe and lower Ala, Arg, Gly, Met, Ser, Thr and Val proportions than bacteria (p < 0.05). The AAN percentage of total N in bacteria and protozoa showed large, unexplained variations, averaging 79.0% and 70.6% (p > 0.05) respectively. Estimation of protozoal contribution to TMN resulted in a cattle-specific mixed model including PCO and DM intake (DMI) per unit of metabolic body size (kg^0.75 ) as fixed effects (RMSE = 3.77). With moderate PCO and DMI between 80 and 180 g/kg^0.75 , which corresponds to a DMI of approximately 10 to 25 kg in a cow with 650 kg body weight, protozoal contribution ranged between 9% and 26% of TMN. Within this range, the estimated protozoal contribution to TMN resulted in minor effects on the total microbial AA pattern.

1.1 Nitrogen Metabolism in the Rumen

The concept that the protein reaching the duodenum of a ruminant comprises of two major components, feed and microbial, has been accepted for many years but recently there has been considerable interest in attempts to define and quantify those processes which have an influence on the quantity and quality of this protein. The main reason for this is the desire to predict accurately the total flow of protein to the duodenum when a particular diet is fed. The ability to do this, coupled with a refinement of knowledge on the needs of the animal, are essential steps in improving the efficiency with which ruminants are fed. This review examines some of the factors which control the breakdown of dietary protein and the synthesis of microbial protein in the rumen. The lack of space has prevented discussion of many important topics, for example, the contribution of endogenous proteins to the total protein entering the duodenum. Many reviews have been published in this area (see Egan, 1980; Demeyer and Van Nevel, 1980; others are referred to in the text).

Microbial contribution to duodenal purine flow in fattening cattle given concentrate diets, estimated by purine N labelling (15N) of different microbial fractions

The origin of duodenal purine bases (PB) was studied in a digestion experiment with four heifers, cannulated in the rumen and duodenum, which received a basal concentrate (152 g crude protein (CP) per kg dry matter (DM)) together with barley straw (85: 15 fresh weight basis) or the same concentrate supplemented with soya-bean meal, carbohydrate-treated soya-bean meal, maize gluten meal or fish meal to increase its protein content to 192 g/kg DM. Tr eatments were assigned to the four animals in five experimental periods according to an incomplete Latin-square design. Each 30-day period included 20 days of change-over adaptation and 10 days of experimental measurements. The flow of digesta entering the duodenum was estimated using Yb and acid-detergent insoluble ash as indigestible markers according to a double-marker system and microbial nitrogen (N) and PB were labelled with15N infused into the rumen. The proportion of duodenal PB of microbial origin estimated from15N enrichment of PB-N averaged 0·66 (s.e. 0·029) and did not differ between treatments nor when protozoa or bacteria associated with liquid (LAB) and solid (SAB) fractions were used as a reference sample. On average microbial contribution to duodenal non-ammonia N was higher when estimated from the PB/N ratio than from15N (0·67 v. 0·55 (s.e. 0·015)) although differences were small and not significant when LAB was the reference sample (0·58 v. 0·52 (s.e. 0·018)) reflecting the higher PB/N ratio of this fraction compared with SAB and protozoa (2·04 v. 1·65 and 1·60 (s.e. 0·04) mmol/g). Considering only the duodenal PB of microbial origin resulted in estimates of microbial N synthesis from the PB/N ratio of SAB similar to those derived from15N enrichment of both bacterial fractions (12·9 v. 13·5 and 13·3 (s.e. 0·83) g/kg of organic matter apparently digested in the rumen OMADR)) but underestimated the values derived from LAB (9·9 g/kg OMADR). Regardless of the estimation method, neither the duodenal flow of microbial N nor the efficiency of microbial synthesis differed between treatments. These results suggest that a significant proportion of duodenal PB have a non-microbial origin which may lead to overestimation of microbial yield when PB are used as a marker. Differences in PB/N ratio between microbial fractions is another important factor to be considered.

The Role of Ciliate Protozoa in the Rumen

First described in 1843, Rumen protozoa with their striking appearance were assumed to be important for the welfare of their host. However, despite contributing up to 50% of the bio-mass in the rumen, the role of protozoa in rumen microbial ecosystem remains unclear. Phylogenetic analysis of 18S rDNA libraries generated from the rumen of cattle, sheep, and goats has revealed an unexpected diversity of ciliated protozoa although variation in gene copy number between species makes it difficult to obtain absolute quantification. Despite repeated attempts it has proven impossible to maintain rumen protozoa in axenic culture. Thus it has been difficult to establish conclusively a role of ciliate protozoa in rumen fiber degradation. The development of techniques to clone and express ciliate genes in λ phage, together with bioinformatic indices to confirm the ciliate origin of the genes has allowed the isolation and characterization of fibrolytic genes from rumen protozoa. Elimination of the ciliate protozoa increases microbial protein supply by up to 30% and reduces methane production by up to 11%. Our recent findings suggest that holotrich protozoa play a disproportionate role in supporting methanogenesis whilst the small Entodinium are responsible for much of the bacterial protein turnover. As yet no method to control protozoa in the rumen that is safe and practically applicable has been developed, however a range of plant extract capable of controlling if not completely eliminating rumen protozoa have been described.

Metabolism of microbial nitrogen in ruminants with special reference to nucleic acids

Characteristically the metabolism of microbial nitrogen (N) compounds in ruminants involves the degradation of dietary N and synthesis of microbial protein (MP), compounds including a small amount of peptides and free amino acids, which may account for 75-85% of total N and the remainder are nucleic acids (NA: DNA and RNA). Generally rumen microbes contain 10-25% NA-N of the total N while 70-80% is in the form of RNA. This paper describes the degradation and synthesis of NA in the rumen and their fate in the lower digestive tracts. Their physiological and nutritional significance in different types of ruminant animals is also discussed. The research works on NA metabolism in ruminants has been mainly on metabolism of purines after rumen microbial digestion and absorption in the lower gut. Subsequently, the fate of absorbed purines has been intensively investigated to assess the extent of MP synthesis in the rumen. The method for predicting ruminal synthesized MP and subsequently digested MP has been proposed using urinary purine derivative (PD) excretion in sheep and cattle fed on ordinary feed. The latter approach has now been adopted for calculation of protein supply in some feeding standards, although there are still difficulties in predicting representative samples of rumen microbes, and also uncertainties in variations of non-renal and endogenous purine losses.

Quantitative analysis of cellulose degradation and growth of cellulolytic bacteria in the rumen

Ruminant animals digest cellulose via a symbiotic relationship with ruminal microorganisms. Because feedstuffs only remain in the rumen for a short time, the rate of cellulose digestion must be very rapid. This speed is facilitated by rumination, a process that returns food to the mouth to be rechewed. By decreasing particle size, the cellulose surface area can be increased by up to 10(6)-fold. The amount of cellulose digested is then a function of two competing rates, namely the digestion rate (K(d)) and the rate of passage of solids from the rumen (K(p)). Estimation of bacterial growth on cellulose is complicated by several factors: (1) energy must be expended for maintenance and growth of the cells, (2) only adherent cells are capable of degrading cellulose and (3) adherent cells can provide nonadherent cells with cellodextrins. Additionally, when ruminants are fed large amounts of cereal grain along with fiber, ruminal pH can decrease to a point where cellulolytic bacteria no longer grow. A dynamic model based on STELLA software is presented. This model evaluates all of the major aspects of ruminal cellulose degradation: (1) ingestion, digestion and passage of feed particles, (2) maintenance and growth of cellulolytic bacteria and (3) pH effects.

Comparison of bacterial pellets and microbial markers for the estimation of the microbial nitrogen and amino acids flows from single flow continuous culture fermenters fed diets containing two-stage olive cake

The effects of using effluent bacteria (EB) and solid- (SAB) and liquid- (LAB) associated bacteria and diaminopimelic acid (DAPA) or purine bases (PB) and partially substituting alfalfa hay (AH) by a concentrate including olive cake on the microbial N flow (MNF) and amino acids (AA) flow were investigated with continuous culture fermenters fed AH and a mixture of AH and a concentrate containing barley grains and two-stage olive cake (2:1 ratio) without (AHCO) or with polyethylene glycol (PEG) (AHCOP). The MNF was not different among diets with SAB or LAB (p = 0.302 and 0.203, respectively) and DAPA, but differed with PB (p = 0.021 and 0.014, respectively). With EB both markers detected similar differences, AHCOP showing a higher value (p < 0.05) than AH and AHCO. The MNF was higher (p < 0.001) with PB than DAPA. Daily flow of non-essential AA was not different (p = 0.356) among diets but essential AA flow was higher (p < 0.05) for AH and AHCOP than for AHCO. The SAB presented lower (p < 0.05) total AA than LAB and higher total AA (p < 0.05) for diet AH than AHCO. The AA profile of EB was similar to that of LAB, but alanine and leucine were higher (p < 0.05) in EB than in LAB. Microbial contribution to AA flow was 45.4%, 55.6% and 58.1% for diets AH, AHCO and AHCOP respectively. With both markers, microbial AA flow was higher (p < 0.05) for diet AHCOP compared with AH (451 and 355 mg/day, respectively), but not different (p > 0.05) for AHCOP and AHCO (389 mg/day). The results would indicate that olive cake could be used in the practical feeding of small ruminants without negatively affecting microbial AA N supply.

Ruminal degradability of15N labelled ribonucleic acid in grass

The ruminal degradation of RNA in rye grass (Lolium perenne) was studied using the bag method. A non-lactating cow (BW 550 kg) fitted with a rumen cannula was used and fed twice daily at maintenance level with a chopped grass hay-based ration containing 30% ground barley. Rye grass, labelled during growth by fertilization with 15N2-urea (9.5 atom% 15N, 20 g N/m2), was cut at seven stages of growth and maturity and freeze-dried. RNA-N represented 6 to 17% of total N. Labelled grass samples (milled to 5.0 mm screen, 5.0+/-0.1 g DM) were incubated in polyester bags (100 x 200 mm, pore size 50 microm) in the rumen for periods of 1, 3, 6, 9, 12, 24, and 48 h. Data of N and RNA disappearances from the bags were fitted to an exponential equation to estimate parameters of degradation. The effective degradability of RNA in the rumen averaged 90+/-4%, for N it was 11% units lower (P < 0.001). Degradability of RNA was correlated to that of N (R2 = 0.92). Degradability of RNA (R2 = 0.96) and N (R2 = 0.93) decreased with increasing fibre content of grass. Increasing the fibre content by 1% diminished the degradability of RNA and N by 1.1% units and 2.4% units, respectively (P < 0.001). Assuming a microbial protein synthesis in the rumen of 150 g/kg DOM, a N: RNA ratio of 1:1.35 in rumen microbes and a rumen outflow rate of 0.06 h(-1), a model calculation indicates that about 9 to 19% of duodenal RNA are of dietary origin in animals fed grass. This should be taken into account for the calculation of microbial N on the basis of RNA as marker.

Determination of diaminopimelic acid in rat feces by high-performance liquid chromatography using the Pico Tag method

The purpose of the study was to develop a method for the determination of diaminopimelic acid (DAPA) concentrations in rat feces by reversed-phase high-performance liquid chromatography (HPLC) using the Pico Tag method. Precolumn derivatization with phenylisothyocyanate (PITC) and UV (254 nm filter) detection were used. Samples were hydrolysed in 6 M HCl at 110 degrees C for 24 h. Hydrolysates were then diluted, dried and derivatized, and samples (10 microliter injected onto a 300x3.9 mm NovaPak C(18) (Waters) HPLC column. Under the conditions used, DAPA eluted as one single peak between those of tyrosine and valine. On-column DAPA concentrations in standards were 41.5-83 pmol, which were in the range of the amounts present in fecal samples of rats fed semisynthetic diets. Amounts of DAPA determined in fecal samples of rats fed broad bean- or chickpea-based diets were, respectively, 2.56 and 2.98 mg g(-1). The advantages of the method and the relevance of the results for nutritional studies in monogastric animals are discussed.

GC-MS analysis of diaminopimelic acid stereoisomers and amino acid enantiomers in rumen bacteria

The amounts and the configuration of the stereoisomers of 2,6-diaminopimelic acid (Dap) and the enantiomeric content of other amino acids were determined in five individual species (Fibrobacter succinogenes, Streptococcus bovis, Selenomonas ruminantium, Prevotella ruminicola and Anaerovibrio lipolytica) of rumen bacteria, and in samples of mixed rumen bacteria isolated from sheep. The separation and quantification of the Dap stereoisomers was achieved by gas chromatography (GC) of trifluoroacetyl 2-propyl esters on a Chirasil-L-Val fused silica column, and detection was achieved by selected ion monitoring mass spectrometry (SIM-MS). No isomers of Dap were detected in S. bovis and P. ruminicola, two of the bacterial isolates. LL- and DD-Dap were not detected in any of the bacterial samples. As only the meso-isomer of Dap was detected in these microorganisms, it was quantified by adding LL-Dap as an internal standard before the bacteria were acid-hydrolyzed. Amounts of between 4.8 and 12.0 mg meso-Dap per gram of bacterial dry matter (DM) were determined. The presence in the rumen bacteria of free amino acid enantiomers, extractable with 70% aqueous ethanol, were determined by GC-SIM-MS; the D-amino acids were predominantly Ala, Asp and Glu, but there was considerable variation between the species.

Determination of rumen microbial-nitrogen production in sheep: a comparison of urinary purine excretion with methods using 15N and purine bases as markers of microbial-nitrogen entering the duodenum

The present study compares estimates of rumen microbial-N production derived from duodenal flow measurements (15N and purine bases) with those from measurements of the urinary excretion of purine derivatives. Four Rasa Aragonesa ewes fitted with simple cannulas in the rumen and proximal duodenum were used. Four diets consisting of 550 g lucerne (Medicago sativa) hay/d as sole feed or supplemented with 220, 400 and 550 g rolled barley grain/d were given in a 4 x 4 random factorial arrangement. Duodenal digesta flows were determined by the dual-phase marker technique during continuous intraruminal infusions of Co-EDTA and Yb-acetate. Microbial contribution to the non-NH3 N (NAN) flow was estimated from 15N enrichment and purines: N ratio in duodenal digesta and bacterial fractions isolated from the rumen content. Whole tract organic matter (OM) digestibility and duodenal flow of OM and NAN increased (P < 0.001) with the level of barley supplementation. Digestible OM intake ranged from 19.0 to 42.7 g/kg metabolic weight (W0.75) and the duodenal flow of purine bases and the urinary excretion of allantoin increased linearly (P < 0.001) from minimum values of 7.47 (SD 1.524) and 4.65 (SD 0.705) mmol/d respectively on the basal diet to 18.20 (SD 1.751) and 11.62 (SD 0.214) mmol/d on the 400 g barley diet; a further increase in barley supplementation decreased both variables (13.50 (SD 2.334) and 8.77 (SD 0.617) mmol/d respectively). Urinary excretion of uric acid and hypoxanthine showed a slight but significant increase (P < 0.05) over all levels of barley. Molar recoveries of duodenal purine bases as purine derivatives or allantoin in the urine were 0.78 (SD 0.156) and 0.65 (SD 0.130) respectively. The increase on barley supplementation significantly augmented microbial-N, but large differences between microbial markers employed were observed. Mean values of microbial-N estimated from the duodenal purine bases or urinary allantoin excretion were on average 18 and 29% lower than those measured by 15N.

The in vitro uptake and metabolism of peptides and amino acids by five species of rumen bacteria

Streptococcus bovis JB1, Prevotella ruminicola B(1)4, Selenomonas ruminantium Z108, Fibrobacter succinogenes S85 and Anaerovibrio lipolytica 5S were incubated with either 14C-peptides (mol. wt, 200-1000) or 14C-amino acids to compare their rates of uptake and metabolism. In experiment 1, the bacteria were grown and incubated in a complex medium, but no uptake of 14C-labelled substrates occurred. When casein digest was omitted, uptake rates of 14C-peptides were different (P < 0.01) with each species, but nil for 14C-amino acids. In experiment 2, to minimize the effects of non-radiolabelled peptides and amino acids, defined and semi-defined media were used. Patterns of 14C-peptide uptake resembled those of experiment 1. The 5-min rate for Strep. bovis JB1 was almost twice that of P. ruminicola B(1)4, though by 15 min they were similar and threefold greater than other species; that of A. lipolytica 5S was especially low. Incubations with 14C-amino acids resulted in a wide range (P < 0.01) of uptake rates; after 5 min P. ruminicola B(1)4 possessed the lowest and Strep. bovis JB1 the highest, but after 15 min, that of Sel. ruminantium Z108 was even higher. All bacteria, with the exception of P. ruminicola B(1)4, assimilated 14C-amino acids faster (P < 0.01) than 14C-peptides. Only Strep. bovis JB1 and P. ruminicola B(1)4 were capable of extensively metabolizing 14C-peptides, but all five species metabolized 14C-amino acids; there was evidence of substantial degradation and some synthesis. Calculations suggest that peptides could supply up to 43%, and amino acids 62% of the N requirements of rumen bacteria.

[Evaluation of different markers for the determination of microbial nitrogen flow into the duodenum of dairy cows]

2,6-Diaminopimelic acid (DAPA), ribonucleic acid (RNA), 15N, D-alanine (D-ALA) and the amino acid profiles (AAP) were compared as microbial markers for determination of the microbial protein synthesis in the rumen. Three dairy cows (Schwarzbuntes Milchrind, LW 602 kg), each fitted with a rumen cannula and a re-entrant cannula in the proximal duodenum, were offered four isoenergetic and isonitrogenous diets (mean daily intake 15.0 +/- 0.45 kg DM; forage: concentrate = 50:50) in a periodic experiment. The diets contained soyabean extracted meal, meat and bone meal, pea meal and dried clover as major sources of protein. On the 4th day after administration of 9 g 15N-labelled urea (95 atom-% 15N-excess) per day, samples of rumen fluid and duodenal digesta were obtained 3 h after feeding. The bacteria were isolated by differential centrifugation. Bacteria harvested from the rumen had significantly higher 15N enrichment and D-ALA: N ratio than 'duodenal' bacteria. However, DAPA: N ratio was higher in 'duodenal' bacteria compared to rumen bacteria. There were no differences in RNA: N ratio between rumen and 'duodenal' bacteria. The source of the bacteria in the digestive tract has an influence on the ratio of microbial N: total N, especially when 15N, AAP, DAPA and D-ALA but not RNA were used as markers. The most reproducible method was D-ALA (C.V. 4.7 for rumen and 6.8 for 'duodenal' bacteria) followed by 15N (10.8 resp. 4.8) and RNA (9.7 resp. 8.2). The results obtained with 15N and D-ALA agreed closely at the same source of bacteria. The RNA method reached the level of these markers (15N, D-ALA) when the bacteria were isolated from the duodenum. It is concluded that D-ALA (bacteria isolated from rumen and duodenum) and also 15N (bacteria isolated from duodenum) were the best markers for estimation of the microbial protein synthesis.

Simulation of the dynamics of protozoa in the rumen

A modified mathematical model is described that simulates the dynamics of rumen micro-organisms, with specific emphasis on the rumen protozoa. The model is driven by continuous inputs of nutrients and consists of nineteen state variables, which represent the N, carbohydrate, fatty acid and microbial pools in the rumen. Several protozoal characteristics were represented in the model, including preference for utilization of starch and sugars compared with fibre, and of insoluble compared with soluble protein; engulfment and storage of starch; no utilization of NH3 to synthesize amino acids; engulfment and digestion of bacteria and protozoa; selective retention within the rumen; death and lysis related to nutrient availability. Comparisons between model predictions and experimental observations showed reasonable agreement for protozoal biomass in the rumen, but protozoal turnover time was not predicted well. Sensitivity analyses highlighted the need for more reliable estimates of bacterial engulfment rate, protozoal maintenance requirement, and death rate. Simulated protozoal biomass was increased rapidly in response to increases in dietary starch content, but further increases in starch content of a high-concentrate diet caused protozoal mass to decline. Increasing the sugar content of a concentrate diet, decreased protozoa, while moderate elevations of the sugar content on a roughage diet increased protozoal biomass. Simulated protozoal biomass did not change in response to variations in dietary neutral-detergent fibre (NDF) content. Reductions in dietary N resulted in an increased protozoal biomass. Depending on the basal intake level and dietary composition, protozoal concentration in the rumen was either increased or decreased by changes in feed intake level. Such changes in relative amounts of protozoal and bacterial biomass markedly affected the supply of nutrients available for absorption. The integration of protozoal, bacterial and dietary characteristics through mathematical representation provided an improved understanding of mechanisms of protozoal responses to changes in dietary inputs.

Evaluation of chemical and physical properties of feeds that affect protein metabolism in the rumen

The goal of the NC-185 Cooperative Regional Research Project is to provide the information needed to improve the nutrition and feeding of dairy cattle, a major factor determining composition of milk and cost of milk yield. Emphasis is placed on understanding how energy and protein nutrition of lactating cows can be manipulated to increase the quantity and improve the profile of AA passing to the small intestine and to improve yield of milk and milk protein. To achieve this goal, one of the major objectives of this project has been to evaluate quantitatively the chemical and physical properties of protein and energy sources that determine AA availability to lactating cows. Reliable measurements of microbial protein synthesis and protein degradation in the rumen are critical in the evaluation process. Therefore, one of the ongoing areas of investigation of this research project has been to determine the most appropriate methods for estimating microbial protein synthesis and dietary protein degradation in the rumen. Other areas have been investigated, using continuous culture fermenters and ruminally and duodenally cannulated cows, including factors that alter microbial metabolism of N in the rumen and subsequently protein supply to the small intestine, such as sources of carbohydrate, protein, and fat and interrelationships of protein and carbohydrate. Findings of the NC-185 Cooperative Regional Research Project Committee and other investigators are summarized in this review.

Variations in the uptake and metabolism of peptides and amino acids by mixed ruminal bacteria in vitro

Mixed ruminal bacteria, isolated from sheep (Q and W) fed a concentrate and hay diet, were anaerobically incubated with either 14C-peptides or 14C-amino acids. Experiment 1 showed that uptake of both 14C-labeled substrates was rapid, but the rate for amino acids was twofold greater than for peptides (molecular weight, 1,000 to 200) initially but was similar after 10 min. Experiment 2 demonstrated that metabolism was also rapid; at least 90% of either 14C-labeled substrate was metabolized by 3 min. Of the radioactivity remaining in bacteria, approximately 30% was in the form of 14C-amino acids, but only in leucine, tyrosine, and phenylalanine. Supernatant radioactivity was contained only in tyrosine, phenylalanine, and mostly proline for incubations with 14C-amino acids but in up to 10 amino acids when 14C-peptides were the substrates. Short-term incubations (< 5 min; experiment 3) confirmed previous uptake patterns and showed that the experimental system was responsive to substrate competition. Experiment 4 demonstrated that bacteria from sheep Q possessed initial and maximum rates of 14C-amino acid uptake approximately fourfold greater (P < 0.01) than those of 14C-peptides, but with no significant differences (P > 0.1) between four 14C-peptide substrate groups with molecular weights of 2,000 to < 200. By contrast, bacteria from sheep W showed no such distinctions (P > 0.1) between rates for 14C-peptides and 14C-amino acids. Calculations suggested that peptides could supply from 11 to 35% and amino acids could supply from 36 to 68% of the N requirements of mixed ruminal bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of diaminopimelic acid in biological materials using high-performance liquid chromatography

A method for the determination of diaminopimelic acid (DAPA) concentrations in feeds and rumen digesta by reversed-phase high-performance liquid chromatography using precolumn derivatization with o-phthaldialdehyde and fluorimetric detection was developed. Samples were oxidized and hydrolysed prior to analyses by HPLC. Hydrogen peroxide and formic acid were used for oxidation; hydrolyses were performed using 3 M hydrochloric acid under vacuum at 120 degrees C for 17 h. Oxidation allowed more space for DAPA-OPA peak elution and hydrochloric acid hydrolysis reduced sample clean-up and extended the column life. Hydrolysates were diluted, adjusted to pH 7 and filtered. A Beckman Model 507 autosampler with a precolumn derivatization cassette was used for the derivatization process and fluorimetric detection was used to measure the OPA derivatives. Samples were prepared in order to have on-column DAPA concentrations in the range 10-100 pmol. The relative recovery of the standard solutions added to the feed samples ranged from 98.4 to 102.8 %. The reproducibility of the method was evaluated by the analysis of eight alfalfa hay samples and eight alfalfa hay samples incubated in the rumen for 48 h and they yielded relative standard deviations of 2.04 % and 2.02%, respectively.

Markers for quantifying microbial protein synthesis in the rumen

Measurement of ruminal microbial protein is necessary to quantify ruminal escape of dietary protein and microbial yields. Microbial markers used most widely have been the internal markers, diaminopimelic acid and nucleic acids (RNA, DNA, individual purines and pyrimidines, or total purines), and the external isotopic markers (e.g., 15N and 35S). Combined with digesta flow markers in ruminally and abomasally or intestinally cannulated ruminants, microbial yields can be estimated. An ideal marker system must account for both the bacterial and protozoal pools associated with both the fluid and particulate phases of digesta. No marker has proven completely satisfactory; hence, yield estimates are relative rather than absolute. Total purines represent robust microbial markers that should be adaptable by most investigators. Principal concerns about total purines relate to unequal purine: N ratios in protozoal and bacterial pools and to the need to assume that dietary purines are completely degraded in the rumen. A theoretically sounder, but more costly, method is continuous intraruminal infusion of 15N ammonium salts. However, 15N enrichments of bacterial and protozoal pools are not equal, so the basis for calculating microbial yield in faunated ruminants is uncertain. Urinary purine excretion may prove to be a noninvasive method for estimating microbial protein yields in intact dairy cows.

Microbial protein synthesis and flows of nitrogen fractions to the duodenum of dairy cows

Attempts have been made to increase nutrient availability for milk production by increasing feed intake, optimizing ruminal fermentation, and supplementing nutrients to the diet that will escape ruminal degradation. Energy and N are the nutritional factors that most often limit microbial growth and milk production. Ruminal fermentation and flow of microbial and dietary protein to the small intestine are affected by feed intake and by the amount and source of energy and protein in the diet. Feeding protein and carbohydrate that are not degraded in the rumen increases the quantity of dietary protein that passes to the small intestine but may decrease the quantity of microbial protein that is synthesized in the rumen. This often results in only small differences in the total NAN that passes to the small intestine. Because microbial protein supplies a large quantity of total AA that passes to the small intestine, differences in passage of individual AA often are only slight. Additional research with cows consuming large amounts of feed are needed to identify combinations of feed ingredients that synchronize availabilities of energy and N for optimizing ruminal digestion, microbial protein synthesis, nutrient flow to the small intestine, and milk production and composition.

DAP-decarboxylase activity and lysine production by rumen bacteria

The last step of pathway of lysine biosynthesis by rumen bacteria was tested. The first measurements of DAP-decarboxylase activity and of lysine production by Megasphera elsdenii, Selenomonas ruminantium, Clostridium spp., Butyrivibrio fibrisolvens and Bacteroides succinogenes as well as the first attempts to increase the lysine production by ruminal streptococci by mutation are described. The highest values were measured in Selenomonas ruminantium (DAP-decarboxylase activity = 146 micrograms DAP.min-1.mg-1 protein and lysine production was 390 micrograms.mg-1 protein) and the lowest values were ascertained in Butyrivibrio fibrisolvens (DAP-decarboxylase activity = 27 micrograms DAP.min-1.mg-1 protein and lysine production was 32 micrograms.mg-1 protein). DAP-decarboxylase activity was increased by mutation especially in Streptococcus bovis, the lysine production in both of tested ruminal streptococci. The potential use of lysine-excreting mutants in calves in future is suggested.

Chromatographic separation of mixed peptides from amino acids in biological digests with volatile buffers

Two chromatographic methods, capable of separating mixed peptides from contaminating amino acids in biological digests, are described. Both methods involve separation on copper-Chelex resin, but each uses a different set of elution buffers. When separation method 1 was applied to a commercially available proteolytic digest of casein, the free amino acid content was reduced from 26.0% to 0.5%. With an enzymic digest of 14C-labelled proteins derived from plant biomass, separation method 2 decreased the contaminating free amino acids from 20.3% to 1.9%. Since the separated peptides are eluted with volatile buffers, they are suitable as substrates for biological experiments.

[Determination of 2,6-diaminopimelic acid in swine feces and chymus]

A method is described for estimation of 2.6-diaminopimelic acid (DAP) using an automated amino acid analyzer and MOORE and STEIN ninhydrin reagent. Investigations were made concerning the influence of sample treatment on DAP content of faeces and ileal digesta of pigs and isolated bacteria. Oxidation before hydrolysis did not change DAP content of faeces and bacterial samples, but increased DAP of digesta. Since analytical reasons were excluded, different accessibility of DAP in faeces and digesta for hydrolysis is suggested. Lyophilization or preservation of fresh samples with formaldehyde and phenolic solution, resp., resulted in no significant influence on DAP content.

In vitro production of lysine from 2,2'-diaminopimelic acid by rumen protozoa

Rumen protozoa can produce lysine from free 2,2'-diaminopimelic acid (DAP). However, the quantitative importance of this transformation has been disputed; lysine contents of protozoal incubation supernatants reported by Onodera & Kandatsu and Masson & Ling show a 26-fold difference. The in vitro experimental methods of both groups were compared to determine the causes of this difference. Lysine production was proportional to DAP concentration. Results with rumen protozoa from sheep or goats were similar. The incubation medium and deproteinizing procedure of the Welsh group gave a two-fold increase in lysine production compared with Japanese protocols. Omissions of rice starch from protozoal incubations slightly increased lysine production, whereas omissions of antibacterial agents resulted in varying, yet relatively small changes. The greatest cause of the difference was the number of rumen protozoa incubated. When this factor was taken into account, the difference in the maximum rates of lysine production between the Welsh and Japanese groups was only three-fold, namely 4.5 versus 15.0 nmol lysine/10(5) protozoa/h. Adding other amino acids to the incubations suggested that DAP uptake by rumen protozoa may occur via transport system ASC. The importance of DAP metabolism by protozoa as a source of lysine for ruminant host animals is discussed.

In vivo metabolism of 2,2'-diaminopimelic acid from gram-positive and gram-negative bacterial cells by ruminal microorganisms and ruminants and its use as a marker of bacterial biomass

Cells of Bacillus megaterium GW1 and Escherichia coli W7-M5 were specifically radiolabeled with 2,2'-diamino[G-3H]pimelic acid ([3H]DAP) as models of gram-positive and gram-negative bacteria, respectively. Two experiments were conducted to study the in vivo metabolism of 2,2'-diaminopimelic acid (DAP) in sheep. In experiment 1, cells of [3H]DAP-labeled B. megaterium GW1 were infused into the rumen of one sheep and the radiolabel was traced within microbial samples, digesta, and the whole animal. Bacterially bound [3H]DAP was extensively metabolized, primarily (up to 70% after 8 h) via decarboxylation to [3H]lysine by both ruminal protozoa and ruminal bacteria. Recovery of infused radiolabel in urine and feces was low (42% after 96 h) and perhaps indicative of further metabolism by the host animal. In experiment 2, [3H]DAP-labeled B. megaterium GW1 was infused into the rumens of three sheep and [3H]DAP-labeled E. coli W7-M5 was infused into the rumen of another sheep. The radioactivity contents of these mutant bacteria were insufficient to use as tracers, but the metabolism of DAP was monitored in the total, free, and peptidyl forms. Free DAP, as a proportion of total DAP in duodenal digesta, varied from 0 to 9.5%, whereas peptidyl DAP accounted for 8.3 to 99.2%. These data reflect the extensive metabolism of bacterially bound DAP within the gastrointestinal tracts of ruminant animals and serve as a serious caution to the uncritical use of DAP as a marker of bacterial biomass in the digesta of these animals.

Ruminal digestion and microbial utilization of diets varying in type of carbohydrate and protein

Three ruminally and duodenally cannulated, lactating Holstein cows were used in a 3 x 3 Latin square experiment to study the effects of differing levels of nonstructural carbohydrate and degradable intake protein on ruminal digestibility and microbial protein production. Three diets were formulated to contain 1) 38 and 13.2%, 2) 31 and 11.8%, and 3) 24 and 9% nonstructural carbohydrate and degradable intake protein as percentages of the DM, respectively. Dry matter intakes were similar for all diets (21.9, 21.1, and 18.3 kg/d for diets 1, 2, and 3, respectively). Likewise, microbial efficiency, as estimated from purine analysis, was unaffected by diet and averaged 24 g of microbial N/kg of OM digested for all treatments. Ruminal digestion of OM averaged 66.6, 65.1, and 55.7% for diets 1, 2, and 3, respectively, resulting in lower microbial N flow per day for diet 3 (317, 333, and 202 g, respectively). Digestion of nonstructural carbohydrate and CP followed similar trends as did OM digestion, whereas NDF digestion remained similar across all diets. These results indicate that nonstructural carbohydrate greater than 24% and ruminally degradable protein greater than 9% of DM will enhance microbial protein flow from the rumen.

Interlaboratory variation in a diaminopimelic acid assay: influence on estimated duodenal bacterial nitrogen flow

Samples of ruminal bacteria and duodenal digesta were collected from two dairy cows fed a 65% forage diet. Samples were sent blind to four laboratories for diaminopimelic acid analysis. Analyzed values differed among laboratories within sample type, and concentrations ranked as follows: laboratory D greater than laboratory A greater than laboratory B greater than laboratory C. Consideration of differences in actual procedures used among laboratories resulted in several hypotheses to explain some of the interlaboratory variation. Using diaminopimelic acid values from each laboratory to estimate duodenal bacterial nitrogen flow showed that laboratory D estimated a 17% higher flow than the average for laboratories A, B, and C, which were similar.

Comparison of nitrogen-15 and diaminopimelic acid for estimating bacterial protein synthesis of lactating cows fed diets of varying protein degradability

Three lactating Holstein cows fitted with duodenal cannulae were fed diets containing cottonseed meal, corn gluten meal, or blood meal as protein supplements in a 3 c 3 Latin square experiment. Diets averaged 15% CP and were 60% concentrate, 31% corn silage, and 9% alfalfa hay. The flow marker was Cr2O3; the bacterial protein fraction of digesta CP was estimated by 15N (as ammonium sulfate) and diaminopimelic acid. The undegraded fraction of total feed protein entering the duodenum for respective diets was .52, .57, and .69. The 15N method was less variable than diaminopimelic acid. Based on 15N, percentage of bacterial of total protein differed among treatments (61.5, 59.4, and 55.0, respectively). Ten percent more protein entered the duodenum on blood meal than other diets, but differences were not significant. Protein sources were similar in microbial passage, but degraded protein was used most efficiently for microbial synthesis on blood meal. Incorporation of 15N consumed into bacterial protein ranged from 50 to 83% with numerically highest values on blood meal, suggesting greater efficiency of ammonia, capture. Recoveries of 15N for the 72 h as milk, feces and urine ranged from 54 to 78%.

[The use of ribonucleic acids as markers for the measuring of microbial protein yield in the rumen. 2. The effect of sample treatment, the time of sampling and the composition of the ration on the RNA:N ratio in rumen microbes]

In two experiments the influence of the treatment of samples, the sampling time and the composition of the rations on the RNA: N ratio in the rumen microbes was checked. Experiment I proved that freezing (-21 degrees C), thawing and freeze-drying of isolated bacteria and protozoa from the rumen fluid and from the duodenal content did not result in a change of the RNA content and the RNA-N: total N relation. If, however, the rumen fluid is stored deep-frozen before the isolation of the bacteria the N content in the DM of the bacteria decreases by 17% and that of RNA by 30%. This results in a change of the RNA: N relation of 16%. In conclusion, the bacteria are to be isolated immediately after rumen fluid sampling. Isolated bacteria can be stored deep-frozen before RNA determination and then freeze-dried. Experiment II showed that the RNA content of the rumen protozoa varies according to the period after feeding. The RNA: N relation was 0.50, 0.92, 0.70 and 0.58 on average 0, 3, 6 and 8 h after feeding, in which the 3rd hour after feeding can obviously be considered the time of increased microbial activity. The conclusion from this variation is that more than one isolation of microbes must be carried out in the course of the day in order to achieve representative samples. These statements apply to easily and not easily fermentable protein as N source in the feed. It could also be proved that no essential variation is to be expected in the RNA: N relation in the microbes isolated from the rumen fluid in the range of 8-21% crude protein in the DM of the ration (roughage: concentrate = 55: 45). On average the rumen microbes contained 1.7 g RNA-N/16 g N, essential differences between bacteria and protozoa could not be ascertained. From the slight variation of the RNA-N: N relation in the isolated bacteria from various cows one can conclude that there is no need to isolate the microbes of each individual animal.

In vitro metabolism of 2,2'-diaminopimelic acid from gram-positive and gram-negative bacterial cells by ruminal protozoa and bacteria

Bacillus megaterium GW1 and Escherichia coli W7-M5 were specifically radiolabeled with 2,2'-diamino[G-3H]pimelic acid [( 3H]DAP) as models of gram-positive and gram-negative bacteria, respectively. These radiolabeled bacterial mutants were incubated alone (control) and with mixed ruminal bacteria or protozoa, and the metabolic processes, rates, and patterns of radiolabeled products released from them were studied. Control incubations revealed an inherent difference between the two substrates; gram-positive supernatants consistently contained 5% radioactivity, whereas even at 0 h, those from the gram-negative mutant released 22%. Incubations with ruminal microorganisms showed that the two mutants were metabolized differently and that protozoa were the major effectors of their metabolism. Protozoa exhibited differential rates of engulfment (150 B. megaterium GW1 and 4,290 E. coli W7-M5 organisms per protozoan per h), and they extensively degraded [3H]DAP-labeled B. megaterium GW1 at rates up to nine times greater than those of ruminal bacteria. By contrast, [3H]DAP-labeled E. coli W7-M5 degradation by either ruminal bacteria or ruminal protozoa was more limited. These fundamental differences in the metabolism of the two mutants, especially by ruminal protozoa, were reflected in the patterns and rates of radiolabeled metabolites produced; many were rapidly released from [3H]DAP-labeled B. megaterium GW1, whereas few were slowly released from [3H]DAP-labeled E. coli W7-M5. Most radiolabeled products derived from [3H]DAP-labeled B. megaterium GW1 were peptides of bacterial peptidoglycan origin. The ruminal metabolism of DAP-containing gram-positive and gram-negative bacteria, even with the same peptidoglycan chemotype, is thus likely to be profoundly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein metabolism in the rumen of silage-fed steers: effect of fishmeal supplementation

1. Ryegrass (Lolium perenne cv. Cropper) silage was given to four Friesian steers (initial live weight (LW) 172 kg) alone or with a fishmeal supplement (150 g fresh weight/kg silage dry matter (DM)) in a balanced two-period change-over design. The dietary components were the same as those used in a recent experiment by Gill et al. (1987). All diets were offered hourly at 24 g DM/kg LW. 2. Fishmeal supplementation increased dietary nitrogen intake (P less than 0.01) and significantly increased the flow of total N (P less than 0.01), non-ammonia N (NAN) (P less than 0.01) and amino acids (P less than 0.05) at the duodenum. The increased supply of NAN to the duodenum was due largely (67%) to increased flow of undergraded dietary protein. 3. Microbial protein production was estimated simultaneously with 15N, diaminopimelic acid (DAPA) and a novel technique using L-[4,5-3H]leucine. Estimates varied with the marker and source of microbial isolate but mean values indicated that microbial N flow was significantly increased by fishmeal supplementation (P less than 0.05). The use of L-[4,5-3H]leucine as a microbial marker is justified and its possible advantages over other markers are discussed. 4. The efficiency of microbial protein synthesis was significantly increased from 30.8 g N/kg organic matter apparently digested in the rumen (OMADR) to 54.3 g N/kg OMADR by fishmeal supplementation (P less than 0.01). However, this indicates that relatively high efficiencies can be achieved with unsupplemented high quality silage supplied continuously. Rumen degradable N (RDN) supply was significantly increased by fishmeal supplementation (P less than 0.05) but apparent efficiency of capture of RDN by rumen microbes was not significantly increased. 5. Attempts were made to investigate the source of N utilized by the microbes on the two diets by intrarumen infusions of (15NH4)2SO4 and L-[4,5-3H]leucine but these were confounded by rumen-mixing problems. Findings obtained suggest that a lower proportion of microbial N may have been derived from rumen ammonia when the silage was supplemented with fishmeal but no differences in the extent of direct incorporation of leucine into microbial protein were observed. This could indicate an increase in microbial peptide uptake on the fishmeal-supplemented diet. However, evidence was also obtained suggesting that the improvement in microbial protein synthetic efficiency with supplementary fishmeal was also due to the provision of a more continuous supply of nitrogenous substrates for microbial growth, as a result of hourly feeding.(ABSTRACT TRUNCATED AT 400 WORDS)

Initial studies on leucine metabolism in the rumen of sheep

1. [3H]leucine infused directly into the rumen of sheep labelled microbial protein and, when compared with the specific activity of the rumen free-leucine pool, indicated that 50% of the bacterial protein leucine originated from the rumen free-leucine pool. 2. The lower limit for bacterial protein turnover in the rumen was 0.37/d when calculated as the difference between the specific rate of disappearances of labelled bacteria from the rumen and the liquid-phase dilution rate. 3. Intravenously infused leucine also labelled the rumen bacteria. The build-up of specific activity in the rumen bacteria was sigmoidal and did not resemble that of the salivary protein which suggested that the rumen epithelium was a major endogenous protein input to the rumen. Additionally, bacteria isolated from the rumen epithelium had high radioactivity indicating that they were ingesting the rumen epithelial cells.