Some effects of variation in carbohydrate and nitrogen intakes on the chemical composition of mixed rumen bacteria from young steers

Evaluation of procedures for detaching particle-associated microbes from forage and concentrate incubated in Rusitec fermenters: efficiency of recovery and representativeness of microbial isolates

Three detachment procedures (DP) were evaluated for their ability to remove particle-associated microbes from digesta in Rusitec fermenters fed a 30:70 alfalfa hay:concentrate diet. Forage and concentrate were incubated in separate nylon bags, and incubation residues were treated independently. Microbial biomass was labeled with (15)NH(4)Cl. Treatments were 1) MET: residues were incubated at 38 degrees C for 15 min with saline solution (0.9% NaCl) containing 0.1% methylcellulose with continuous shaking; 2) STO: residues were mixed with cold saline solution and homogenized with a stomacher for 5 min at 230 revolutions per min; and 3) FRE: residues were immediately frozen at -20 degrees C for 72 h, thawed at 4 degrees C, mixed with saline solution, and subjected to STO procedure. Common to all treatments was storing at 4 degrees C for 24 h after the treatment, homogenization, filtration, and resuspension of residues 2 times in the treatment solutions. Microbial pellets were obtained by centrifugation, and microbial removal was estimated indirectly by measuring removal of (15)N. The PCR-single-stranded conformation polymorphism analysis of the 16S ribosomal DNA was used to analyze the similarity between microbial communities attached to the substrate and those in the pellet obtained after each DP. There were no feed x DP interactions (P = 0.16 to 0.96) for any variable, except for N content in microbial pellets (P = 0.02). Detaching efficiency (P = 0.004) and total recovery (P = 0.01) were affected by DP, with STO showing the greatest values (mean values across substrates of 64.1% for detaching efficiency and 58.3% for total recovery) and MET the least values (57.0 and 51.8%). Similarity index between the microbes attached to substrates and those in the pellets were affected (P = 0.02) by DP, with MET showing greater (P < 0.02) values (84.0 and 86.4% for forage and concentrate, respectively) than FRE (72.5 and 67.8%) and STO having intermediate values (77.1 and 82.4%). There were no differences (P = 0.70) among particle-associated microbe pellets in their N content, but MET pellets had greater (P < 0.05) (15)N enrichments than those obtained by STO and FRE. Although STO was the most effective method to detach ruminal microbes from concentrate and forage, MET produced pellets with the greatest similarity to the microbial communities attached to the substrates and therefore could be considered the most appropriate DP method for treating digesta from Rusitec fermenters.

Diet and procedures used to detach particle-associated microbes from ruminal digesta influence chemical composition of microbes and estimation of microbial growth in Rusitec fermenters

Four different detachment methods were evaluated for their ability to remove particle-associated microorganisms (PAM) from ruminal digesta in semicontinuous fermenters fed two diets differing in their forage:concentrate ratio (80:20 [C20] and 20:80 [C80]). In the methylcellulose method, ruminal digesta was incubated at 38 degrees C for 15 min with saline solution containing 0.1% methylcellulose before being stored at 4 degrees C for 24 h. In the other procedures, samples were incubated with 0.1% methylcellulose before storage for 24 h at 4 degrees C in different solutions (pH = 2): 1) saline solution with 0.1% Tween 80; 2) saline solution with 0.1% Tween 80 and 1% tertiary butanol; and 3) saline solution with 0.1% Tween 80, 1% methanol, and 1% tertiary butanol. Common to all treatments was subsequent homogenization, followed by filtration and resuspension of the residue five times in the treatment solutions. Microbial removal was estimated indirectly by measuring removal of 15N. There were no differences (P > 0.05) among detachment procedures, neither in the detaching efficiency (mean values of 79.7 and 88.1% for C20 and C80 diets, respectively) nor in the total recovery of PAM (54.9 and 34.9% for C20 and C80, respectively). There were no differences (P > 0.05) among PAM pellets obtained by the different detachment procedures in their N content, purine bases (PB) concentration, or PB:N ratio. For the C80 diet, 15N enrichment was greater (P < 0.05) in PAM pellets obtained with methylcellulose than in those obtained by the other methods. However, there were no differences (P > 0.05) due to the detachment procedure in the values of daily microbial growth estimated using as reference the different PAM pellets. The PAM pellets for diet C20 presented greater (P < 0.01) N content and lower (P < 0.01) PB concentration than those for diet C80 (mean values of 74.3 vs 49.1 mg of N/g of dry matter, and 22.8 vs 26.0 micromol PB/mg of dry matter, respectively). Daily microbial growth was greater (P < 0.05) for the C80 diet than for the C20 diet (121 vs 114 mg of microbial N, respectively). Results suggest that the treatment of ruminal digesta with a saline solution with 0.1% methylcellulose at 38 degrees C for 15 min combined with homogenizing and chilling at 4 degrees C for 24 h removed a major proportion of PAM, although further research is needed to decrease microbial losses during the isolation process.

Effects of type of carbohydrate supplementation to lush pasture on microbial fermentation in continuous culture

Eight single-flow continuous culture fermenters were used to study the effects of the type of energy source on ruminal N utilization from high quality pasture. The four dietary treatments included high quality grass and legume pasture alone (50:50; wt/wt), pasture plus soybean hulls, pasture plus beet pulp, and pasture plus corn. Diets supplemented with additional sources of energy (soybean hulls, beet pulp, and corn) were isocaloric but differed in the type and rate of carbohydrate fermentation. Energy supplements constituted 45% of the total dietary dry matter and were fed twice daily at 12-h intervals in place of pasture, which is characteristic of grain feeding at milking when animals are in a grazing situation. Energy supplementation reduced pH, NH3 N flow, and NH3 N concentration and increased bacterial N flow (as a percentage of N intake). The supplementation of corn and soybean hulls resulted in the highest microbial N flow (as a percentage of N intake). Corn had a tendency to reduce fiber digestion because of excessively low NH3 N concentrations. Beet pulp was similar to corn in that it decreased NH3 N concentrations. Supplementation of soybean hulls resulted in a more synchronized fermentation, greater volatile fatty acid production, and greater fiber digestion. Nitrogen utilization by microbes was maximized by supplementation with soybean hulls or corn twice a day. With diets based on pasture, it may be more important to improve bacterial N flow and bacterial utilization of N than to maximize the efficiency of bacterial protein synthesis because better utilization of N by ruminal microorganisms results in higher bacterial N flow and higher fiber digestion.

Different mathematical approaches to estimating microbial protein supply in ruminants

Many of the amino acids that are available for absorption in ruminants are derived from microbial protein that has been synthesized in the reticulorumen. This paper focuses on the prediction of the microbial protein supply and evaluates different approaches to represent mathematically the process of microbial protein synthesis. In current protein evaluation systems for ruminants, the microbial protein supply is predicted using empirical equations that relate microbial protein production to the amounts of ruminally available energy and nitrogen. In contrast, mechanistic models of rumen function endeavor to describe quantitatively the microbial protein production that is based on underlying identifiable processes. A brief description is presented of two culture techniques used to examine microbial ecosystems, namely, batch culture and chemostat culture. The mathematical equations describing these cultures are helpful in understanding key parameters of microbial production for inclusion in models, including specific growth rate, growth yield, and substrate affinity. The availability of carbohydrates is a primary determinant of microbial protein production in the rumen, and the adequacy of mathematical representations of this relationship in empirical and mechanistic models is assessed. The representation of substrate utilization for nongrowth processes and the relationship between microbial protein production and the availability of various nitrogen sources are discussed. A variable part of the synthesized microbial protein does not reach the duodenum but is degraded in the rumen, and its representation is examined. The prediction of microbial protein supply should be based on a sound representation of the underlying mechanisms, including the interactions among microbes and between microbial activity and substrate degradation.

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.

Composition of ruminal bacteria harvested from steers as influenced by dietary energy level, feeding frequency, and isolation techniques

The effects of isolation techniques and time of sampling on composition of ruminal bacteria were examined in four steers fed two energy levels (2.24 or 2.92 Mcal metabolizable energy/kg DM) at two feeding frequencies. Diets were alfalfa hay and corn silage or ground corn/corn silage and were fed twice or 12 times daily. Whole ruminal contents were collected at four time intervals over a 4-d period. Fluid- and particle-associated bacteria were isolated. Energy level, feeding frequency, and preisolation freezing had little effect on composition of bacteria. Sampling time did not affect composition of bacteria harvested from steers fed frequently but had linear and quadratic effects on concentrations of cell components of bacteria harvested from steers fed twice daily. Differences were observed in the composition of bacteria harvested from the fluid phase compared with particle-associated or mixed populations of ruminal bacteria. These differences translated into different estimates of bacterial N supplied to the small intestine depending on N:purine ratio used. Composition of bacteria may be affected by fraction of contents sample and by time of sampling for animals fed infrequently. Freezing of samples before isolation of mixed bacteria does not appear to affect composition or estimates of bacterial N flows to the small intestine.

[The effect of different centrifugation conditions in the isolation of mixed rumen bacteria on their content of nitrogen and diaminopimelic acid: use of duodenal content as raw material]

The objective of the present study was, to investigate the effect of varying conditions of differential centrifugation of duodenal content on the isolation of bacteria (B-fraction) and feed particles + protozoa (FP-fraction). The treatments at low-speed centrifugation were as follows: 100 x g/5 min, 400 x g/10 min, 1000 x g/10 min and 2000 x g/10 min, high speed conditions were 30,000 x g/30 min/4 degrees C. The results of three experiments are given. Analytical examination gave similar results for N-contents for all treatments, the mean values being 7.90 +/- 0.27% (n = 12) for B-fractions and 6.53 +/- 0.73% (n = 12) for FP-fractions. Increasing the low-speed from 100 x g to 2000 x g lead to increasing DAP-contents and decreasing N:DAP-ratios of the bacterial isolates, the values being 2.43, 3.02, 3.22 and 3.39 mg DAP/g DM and 32.0, 27.4, 25.0 and 23.0 N:DAP-ratio. Decreased isolation of bacterial material in the B-fraction in conjunction with increased incorporation in the FP-fraction resulted in rising the speed of the low speed centrifugation. The rates of loss of DAP, measured by comparison with the total amount were 10, 32, 48 and 70% respectively. It was concluded to prefer the isolation of bacteria from rumen fluid.

Effect of different levels of phosphorus on rumen microbial fermentation and synthesis determined using a continuous culture technique

A continuous culture technique was used to study the phosphorus requirements of rumen micro-organisms. Solutions of artificial saliva containing 120, 80, 40 and 0 mg inorganic phosphorus (Pi)/l were infused into the reaction vessels previously inoculated with rumen contents, resulting in Pi concentrations in the vessel contents of 48, 28, 4 and less than 1 mg/l respectively. Various fermentative and synthetic characteristics were examined. In the vessel contents, concentrations of protozoa (about 0.9 X 10(5)/ml) were not significantly affected by Pi concentration. Total volatile fatty acids (VFA) produced averaged about 6.83 mmol/h with Pi levels of 48 and 28 mg/l. Reduction in Pi concentrations to 4 and less than 1 mg/l resulted in significant reductions in total VFA to approximately 6.25 and 3.75 mmol/h respectively, accompanied by a rise in pH from 6.5 to 7.3. Ammonia-nitrogen values, which averaged about 131 mg/l at the higher Pi concentrations, also increased with the lowest level of Pi to about 240 mg/l. ATP concentrations averaged about 14 mumol/l at the highest Pi concentration and fell progressively with each reduction in Pi concentration to a final value of 2.5 mumol/l with the Pi level less than 1 mg/l. At Pi concentrations of 48 and 28 mg/l, the digestibilities of xylose, arabinose and cellulose-glucose were maintained at about 0.90, 0.62 and 0.70 g/g input respectively. At lower Pi concentrations these digestibilities fell significantly and corresponding values at Pi less than 1 mg/l were 0.73, 0.41 and 0.31 respectively. Starch digestion was unaffected by Pi concentration and remained at about 0.90 g/g input. The amount of microbial-N synthesized averaged 0.48 g/d and was maintained with Pi concentrations down to 4 mg/l. There was, however, a significant reduction to 0.26 g/d with Pi concentrations of less than 1 mg/l. The efficiency of microbial protein synthesis was variable but averaged approximately 25 g N/kg total carbohydrate fermented. It was estimated that the minimum Pi concentrations required in rumen fluid in vivo to maintain maximum degradative and synthetic microbial activities was in the range 75-100 mg/l and that over-all P requirement of the microbes was of the order of 5.1 g/kg apparently digested organic matter intake.

[Protein and amino acid metabolism in the digestive tract growing young bulls. 1. Flow of bacterial raw protein in the duodenum determined by 2,6-diaminopimelic acid as a marker]

The influence of the composition of the rations on the content of diamino pimelic acid (DAP) and N in the bacteria dry matter and on the flow of bacteria crude protein into the duodenum, determined with DAP as marker, was determined on the basis of experimental investigations with young bulls provided with duodenal cannulae and with 28 different rations whose details are described. At a production level corresponding to dry matter intake and a variation range of the crude fibre content of between 11.3 and 29.1% in the DM, a content of N-free extractives between 50.9 and 77.4% in the DM, a content of soluble carbohydrates ibetween 5.3 and 6.4% in the DM, a crude protein content of between 6.4 and 17.1% in the DM and a pure protein content of between 4.9 and 15.5% in the DM, the DAP content of the bacteria DM amounts the 0.350 g 100 g DM +/- 0.090 the N-content of the bacteria DM amounts to 7.37 +/- 1.08 g/100 g DM, there are no relations between DAP- and N-content in the bacteria DM and the content of the individual carbohydrate fractions of the ration, there are positive relations between DAP- and N-content of the bacteria DM, the flow of bacterial crude protein into the duodenum amounts to 133 +/- 14 g/kg truly fermentable organic matter or 130 +/- 14 g/kg apparently digestible organic matter, there is a negative relation between bacteria crude protein at the duodenum (BCPD)/kg truly fermentable organic matter and the crude fibre content of the ration, there is a positive relation between BCPD/kg truly fermentable organic matter and N-free extractives and soluble carbohydrate content as well as the digestibility of the organic matter of the ration, there is no specific influence of the flow rate (kg digesta/kg intake of org. matter) or the dilution rate (g bacteriafree org. matter D/kg LW075/b) on BCPD/kg truly fermentable org. matter, there is a dependence of BCPD/kg truly fermentable org. matter on crude protein concentration in the ration in the concentration range of 6.4-9.0% crude protein in the ration (provided endogenous CP equivalents are used).

Protein-energy interrelationships in dairy cows

In dairy cows two distinct and important aspects of the interrelationship between protein and energy-yielding nutrients can be identified. First, a change of protein input can influence performance by changing overall plane of nutrition. To a large extent this results from changes of digestibility and associated intake of ration ingredients. Within this context it appears that at high levels of feeding rumen microbial demand for nitrogen per unit fermentable organic matter is high; initial failure to meet this need for nitrogen probably accounts for many responses to protein supplementation in practice through stimulation of ruminal digestion. Second is that changing "protein" supply to tissues can alter the pattern and efficiency of absorbed nutrient use. In early lactation protein supplementation favors partition of available nutrients toward mammary secretion. There are effects on glucose and fatty acid metabolism, all interacting with the endocrine system within a metabolic framework that tends to conserve those nutrients (amino acids, glucose) that are in shortest supply relative to demand. Response to increased input of amino acids depends both on physiological state of the cow and balance of all nutrients absorbed from the gastrointestinal tract.

The efficiency of microbial protein synthesis in the rumen and the degradability of feed nitrogen between the mouth and abomasum in steers given different diets

Protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with barley straw (BS) or alkali-treated barley straw (BSA). Other diets were supplemented with urea (BSU and BSAU respectively) or with fish meal replacing the tapioca (BSF and BSAF respectively). The diets were isoenergetic and calculated to provide sufficient metabolizable energy (ME) to support a growth rate of 0.5 kg/d. Rumen-degradable nitrogen (RDN):ME values (g/MJ) were estimated to be 0.50, 1.20 and 0.80 for the basal diet, urea- and fish-meal-supplemented diets respectively. RNA and alpha,epsilon-diaminopimelic acid (DAP) were used as microbial markers. 103Ruthenium and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Samples of mixed bacteria separated from rumen digesta from animals receiving N-supplemented diets contained significantly more N than those from animals receiving basal diets (approximately 74 and 62 mg/g dry matter (DM) respectively) but there were no other significant differences in total-N contents between treatments. RNA-N:total-N values were similar for all diets (approximately 0.13). DAP-N:total-N values were significantly lower in bacteria from animals receiving alkali-treated (AT) rather than untreated (UT) straw (approximately 0.008 and 0.011 respectively). The proportion of OM intake digested in the rumen (ADOM) was significantly higher for animals receiving AT straw rather than UT straw (approximately 0.54 and 0.43 respectively). N supplementation had no effect on OM digestibility.(ABSTRACT TRUNCATED AT 250 WORDS)

The nutritive value of rumen micro-organisms in ruminants. 1. Large-scale isolation and chemical composition of rumen micro-organisms

A method is described whereby a large quantity of rumen microbial dry matter of high purity was isolated from whole rumen contents obtained from abattoirs, by means of a continuous process of one filtration through four sieves followed by three differential centrifugations. The contents of ash, carbohydrate, lipid, nitrogen, RNA, DNA and individual amino acids of the three centrifugal fractions are given and compared with values summarized from more than sixty published reports on the chemical composition of rumen micro-organisms isolated from both whole rumen contents and pure cultures. The amino acid composition of isolated rumen micro-organisms, in particular that of the bacteria, was found to be remarkably constant.

Effect of diet on amino and nucleic acids of rumen bacteria and protozoa

Amino acid composition and nucleic acid content of pure cultures of rumen bacteria (17 species) were analyzed. Amino acid composition between gram-positive and -negative organisms was not different. The total nitrogen content of gram-negative bacteria (10.8%) was significantly higher than gram-positive organisms (9.9%). Deoxyribonucleic acid-nitrogen: total nitrogen (mg/g) differed between gram-positive (8.8) and gram-negative (18.9) bacteria, but there was no significant difference in ratio of ribonucleic acid-nitrogen to total nitrogen. In a second experiment six rumen-fistulated cattle were fed either a high roughage (85% alfalfa hay plus 15% concentrate) or high concentrate diet (15% alfalfa hay and 85% concentrate). Cattle were adapted 14 days and rumen contents sampled on 3 consecutive days. Nitrogen content was higher in protozoa from cattle fed low concentrate (8.4%) than in protozoa from cattle fed high concentrate (7.9%) but was similar in bacteria for both diets. Deoxyribonucleic acid nitrogen: total nitrogen (mg/g in bacteria decreased from 27.2 in cattle fed the low concentrate diet to 20.9 in those fed the high concentrate diet. Differences between sampling days were significant for both bacteria and protozoa for ratio of deoxyribonucleic acid-nitrogen to total nitrogen but were significant only in protozoa for ratio of ribonucleic acid nitrogen to total nitrogen. Ribonucleic acid may serve as a marker for estimating microbial production in the rumen if sources of variation are recognized and corrected adequately.

Changes in the composition of digesta during passage through the small intestines of steers

1. Dry matter (DM), organic matter (OM), nitrogenous constituents, carbohydrate constituents and pH were estimated in digesta taken from eight different sites in the small intestines of slaughtered steers given different diets. Amounts of constituents passing different sites were compared using cellulose as a non-digestible marker. 2. Amounts of the different constituents entering the small intestines varied with the type of diet given but the patterns of removal of each constituent were similar regardless of diet. 3. DM and OM were uniformly down the length of the small intestines. Net digestibilities of 0.62 and 0.63 for DM and OM respectively of the amounts measured in segment 1 digesta (first 3 m post-pylorus) were found at the terminal ileum. DM and OM contents of segment 1 digesta were 5 and 8% higher respectively than in abomasal digesta. Significantly smaller amounts of digesta were found in the proximal quarter of the small intestines than in more distal sections. There was a 10% addition of water to digesta in segment 1 compared with abomasal digesta. Of the water entering the small intestines a net 65% was absorbed therein, most absorption occurring in the first half. 4. Ammonia nitrogen was removed uniformly down the length of the small intestines to a net extent of 75% of that in segment 1 digesta. There was an apparent increase of approximately 18% in the total N (TN) content of segment 1 digesta compared with abomasal digesta. There was an approximate net removal of 80% of the TN measured in segment 1 digesta during passage down the small intestines. Over 95% of the digestible TN was removed in the section of tract between 3 and 15 m from the pylorus. Net removal of nucleic acid N (NA-N) up to the distal ileum was 78% of that in segment 1 digesta, most removal occurred in the proximal quarter of the small intestine. Little or no net loss of diaminopimelic acid-N (DAP-N) occurred in the small intestine. 5. Of the carbohydrates entering the small intestines, there was little or no removal of rhamnose, arabinose or xylose. Net removal of ribose, mannose, galactose and 'starch' glucose up to the distal ileum was 82, 76, 54 and 70% respectively of the amounts found in segment 1 digesta. All disappeared uniformly down the length of the small intestine.

Quantitative studies of food protein degradation and the energetic efficiency of microbial protein synthesis in the rumen of sheep given chopped lucerne and rolled barley

1. In a randomized block design, four sheep were given 800 g daily of diets containing: chopped lucerne (L), chopped lucerne-rolled barley (2:1; LB), rolled barley-chopped lucerne (2:1; BL), rolled barley (B); each diet was supplemented with minerals, vitamins and urea as considered necessary. Chronic oxide was included in the diets as a flow marker. 2. Flows of organic matter (OM) and non-ammonia-nitrogen (NAN) to the small intestine (SI) were measured and microbial protein was identified by a 35S-incorporation procedure. 3. OM disappearance in the rumen increased linearly with increasing inclusion of barley in the diet but there was no significant change in microbial NAN flow to the SI so that the yield of microbial NAN (g)/kg fermented OM (FOM) decreased from 29.6 (diet L) to 22.7 (diet B). Changes in the energetic efficiency of microbial protein synthesis appeared to be unrelated to alterations in rumen fluid volatile fatty acid (VFA) proportions or in rumen fluid dilution rate (D). 4. The degradability of dietary protein (non-urea-N), estimated using the 35S procedure, was 0.72, 0.76, 0.86 and 0.86 for diets L, LB, BL and B respectively. Similar values were obtained from concurrent polyester-bag experiments when the fractional outflow rate of undegraded protein from the rumen (k) was assumed to be 0.046.

[Studies on the effect of phosphoric phenyl ester diamide as inhibitor of rumen urease in dairy cows. 3. Digestibility of the nutrients and bacterial protein synthesis]

Two lactating cows with duodenal re-entrance cannulae were fed with rations containing 180g urea (A) resp. urea modified with the urase inhibitor phosphoric phenyl ester diamide (PPD, 1 g PPD/100 g N). The cows, accustomed to urea, were not adapted to PPD (B) resp. had been adapted to PPD for 30 days (C). From A to C the digestibility of the organic matter in the stomachs amounted to 52, 47 and 52% and in the total tract to 78, 77 and 79%; the digestibility of crude cellulose amounted to 64, 50 and 62% resp. 69, 64 and 68% and that of starch to 91, 87 and 95% resp. 100% in each case. 71, 66 and 70% of the N were digested. The passage rate of N in the duodenum was 90, 102 and 106% of the N-intake. In the intestines 61, 68 and 76% of the N-intake were absorbed. The passage of bacteria-N in the duodenum was 67, 92 and 71% of the N-intake, that of the sum of NH3- and urea-N 6,8 and 8%. The conclusion is that, with unchanged digestibility of darbydrates, the N-supply of cows should be improved by the modification of urea with PPD after the adaptation of the cows. Cellulose fermentation is inhibited at the beginning of the adaptation to PPD.

Differential carbohydrate media and anaerobic replica plating techniques in delineating carbohydrate-utilizing subgroups in rumen bacterial populations

A basal (BC) medium devoid of added carbohydrates, a complete (CC) medium containing nine carbohydrates were developed for enumerating rumen bacteria. The colony counts on the BC medium were 85 to 100% of those obtained on the CC medium. These colonies were pinpoint size (less than or equal to mm in diameter) but increased in size (2 to 5 mm in diameter) when carbohydrates were subsequently added. With the CC medium or other media tested, the colony counts were 20 to 50% higher on plates than on roll tubes and were about 35% of the direct cell counts. The lower colony counts on roll tubes were shown to result primarily from the loss of viability due to heat stress. The DC media were found by plating techniques to be suitable for differentiating mixed rumen bacterial populations into subgroups based upon carbohydrate utilization as shown by differences in subgroup profiles found within solid and liquid fractions of rumen contents, within rumen contents from animals fed high-forage and high-grain diets, and by correct colony formations by pure cultures of rumen bacteria on appropriate DC media. With simple modifications and use of an anaerobic glove box, replica plating methods and the CC and DC media were found to be a suitable means of rapidly determining the range of utilizable carbohydrate energy sources of rumen bacteria.

[2,6-Diaminopimelic acid (DPA) content and the DPA:N ratio in rumen bacteria in relation to time after feeding]

The interrelation between the time of the withdrawal of rumen fluid and the DPA: N-relation in the fraction of mixed rumen bacteria was ascertained in a test with two cows with rumen fistulae. At the moment of feeding the DPA-content of 63 mg per g bacteria was very high. In the period of 3 to 9 hours after feeding it remained relatively constant (50 mg). A mean conversion relation of 20.4 of DPA to bacteria N was ascertained. The amino acid model proved to be the same in all fractions, the content values were comparable to those found in technical literature.