Efficiency Of Bacterial Protein Synthesis Research Articles

Supplementing branched-chain volatile fatty acids in dual-flow cultures varying in dietary forage and corn oil concentrations. I: Digestibility, microbial protein, and prokaryotic community structure

Branched-chain amino acids are deaminated by amylolytic bacteria to branched-chain volatile fatty acids (BCVFA), which are growth factors for cellulolytic bacteria. Our objective was to determine the dietary conditions that would increase the uptake of BCVFA by rumen bacteria. We hypothesized that increased forage would increase cellulolytic bacterial abundance and incorporation of BCVFA into their structure. Supplemental polyunsaturated fatty acids, supplied via corn oil (CO), should inhibit cellulolytic bacteria growth, but we hypothesized that additional BCVFA would alleviate that inhibition. Further, supplemental BCVFA should increase neutral detergent fiber degradation and efficiency of bacterial protein synthesis more with the high forage and low polyunsaturated fatty acid dietary combination. The study was an incomplete block design with 8 dual-flow continuous cultures used in 4 periods with 8 treatments (n = 4 per treatment) arranged as a 2 × 2 × 2 factorial. The factors were: high forage (HF) or low forage (LF; 67 or 33%), without or with supplemental CO (3% dry matter), and without or with 2.15 mmol/d (which included 5 mg/d of 13C each of BCVFA isovalerate, isobutyrate, and 2-methylbutyrate). The isonitrogenous diets consisted of 33:67 alfalfa:orchardgrass pellet, and was replaced with a concentrate pellet that mainly consisted of ground corn, soybean meal, and soybean hulls for the LF diet. The main effect of supplementing BCVFA increased neutral detergent fiber (NDF) degradability by 7.6%, and CO increased NDF degradability only in LF diets. Supplemental BCVFA increased bacterial N by 1.5 g/kg organic matter truly degraded (6.6%) and 0.05 g/g truly degraded N (6.5%). The relative sequence abundance decreased with LF for Fibrobacter succinogenes, Ruminococcus flavefaciens, and genus Butyrivibrio compared with HF. Recovery of the total 13C dose in bacterial pellets decreased from 144 µg/ mg with HF to 98.9 µg/ mg with LF. Although isotope recovery in bacteria was greater with HF, BCVFA supplementation increased NDF degradability and efficiency of microbial protein synthesis under all dietary conditions. Therefore, supplemental BCVFA has potential to improve feed efficiency in dairy cows even with dietary conditions that might otherwise inhibit cellulolytic bacteria.

Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. II: Relation with solid passage rate and pH on neutral detergent fiber degradation and microbial function in continuous culture

To support improving genetic potential for increased milk production, intake of digestible carbohydrate must also increase to provide digestible energy and microbial protein synthesis. We hypothesized that the provision of exogenous branched-chain volatile fatty acids (BCVFA) would improve both neutral detergent fiber (NDF) degradability and efficiency of microbial protein synthesis. However, BCVFA should be more beneficial with increasing efficiency of bacterial protein synthesis associated with increasing passage rate (kp). We also hypothesized that decreasing pH would increase the need for isobutyrate over 2-methylbutyrate. To study these effects independent from other sources of variation in vivo, we evaluated continuous cultures without (control) versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate), low versus high kp of the particulate phase (2.5 vs. 5.0%/h), and high versus low pH (ranging from 6.3 to 6.8 diurnally vs. 5.7 to 6.2) in a 2 × 2 × 2 factorial arrangement of treatments. Diets were 50% forage pellets and 50% grain pellets administered twice daily. Without an interaction, NDF degradability tended to increase from 29.7 to 35.0% for main effects of control compared with BCVFA treatments. Provision of BCVFA increased methanogenesis, presumably resulting from improved NDF degradability. Decreasing pH decreased methane production. Total volatile fatty acid (VFA) and acetate production were decreased with increasing kp, even though true organic matter degradability and bacterial nitrogen flow were not affected by treatments. Decreasing pH decreased acetate but increased propionate and valerate production, probably resulting from a shift in bacterial taxa and associated VFA stoichiometry. Decreasing pH decreased isobutyrate and isovalerate production while increasing 2-methylbutyrate production on a net basis (subtracting doses). Supplementing BCVFA improved NDF degradability in continuous cultures administered moderate (15.4%) crude protein diets (excluding urea in buffer) without major interactions with culture pH and kp.

Effect of sprouted barley grain supplementation of an herbage-based or haylage-based diet on ruminal fermentation and methane output in continuous culture

A 4-unit dual-flow continuous-culture fermentor system was used to assess the effect of supplementing 7-d sprouted barley (SB) or barley grain (BG) with an herbage-based or haylage-based diet on nutrient digestibility, volatile fatty acid (VFA) profiles, bacterial protein synthesis, and methane (CH4) output. Treatments were randomly assigned to fermentors in a 4×4 Latin square design with a 2×2 factorial arrangement using 7 d for diet adaptation and 3 d for sample collection. Experimental diets were (1) 55.5g of herbage dry matter (DM) + 4.5g of SB DM, (2) 56.0g of herbage DM + 4.0g of BG DM, (3) 55.5g of haylage DM + 4.5g of SB DM, and (4) 56.0g of haylage DM + 4.0g of BG DM. Forages were fed at 0730, 1030, 1400, and 1900h, whereas SB and BG were fed at 0730 and 1400h. Gas samples for CH4 analysis were collected at 0725, 0900, 1000, 1355, 1530, and 1630h on d 8, 9, and 10. Fluid samples were taken once daily on d 8, 9, and 10 for pH measurements and for ammonia-N and VFA analysis and analyzed for DM, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber for determination of nutrient digestibilities and estimation of bacterial protein synthesis. Orthogonal contrasts were used to compare the effect of forage source (haylage vs. herbage), supplement (BG vs. SB), and the forage × supplement interaction. Apparent and true DM and organic matter digestibilities as well as apparent crude protein digestibility were not affected by forage source. However, true DM digestibility was greatest for diets supplemented with SB. Apparent neutral and acid detergent fiber digestibilities of herbage-based diets were higher than haylage-based diets but fiber digestibility was not affected by supplement. Diets supplemented with SB had higher mean and minimum pH than BG; however, maximum pH was not affected by diet. Supplementation with BG produced a greater concentration of total VFA compared with diets supplemented with SB. Haylage-based diets produced greater CH4 output compared with herbage-based diets but supplementation did not affect CH4 output. Efficiency of bacterial protein synthesis was greater for herbage-based diets compared with haylage-based diets, with no effect of supplementation. Overall, supplementation with SB marginally increased true DM digestibility of herbage- and haylage-based diets but did not affect fiber and crude protein digestibilities, CH4 output, and bacterial efficiency, compared with BG.

Effects of partially replacing dietary starch with dry glycerol in a lactating cow diet on ruminal fermentation during continuous culture

The effects of dry glycerol as a partial replacement for dietary starch in a lactating cow diet on ruminal fermentation and bacterial protein synthesis were evaluated using 4 single-flow, continuous-culture fermentors (ranging from 1,015 to 1,040mL in volume). The basal lactating cow diet was formulated to have partial contents of dietary starch provided from a corn starch supplement [at 12.37% diet dry matter (DM)], which was partially or completely replaced by a dry glycerol product. Both the corn starch supplement and dry glycerol product contained 65% of pure corn starch or glycerol, respectively. The final inclusion rate for pure glycerol was at 0, 3, 5, or 8% of DM in the basal diet. The experiment was conducted using a 4×4 Latin square design with four 9-d periods, with the first 6 d for adaptation and last 3 d for sampling. Fermentors were inoculated with 1L of ruminal fluid and 25g of ruminal digesta from a ruminally cannulated cow receiving a lactation total mixed ration (16% crude protein, 32% neutral detergent fiber, and 25% starch; DM basis). Each fermentor was fed 75g of DM of its respective experimental diet daily in 3 equal portions (at 0800, 1400, and 2000h). Liquid dilution rate of the fermentors was maintained at 10%/h and solids retention time was set at 24h. Fermentation fluid and the effluent from each fermentor were sampled once daily (at 1330h) from d 7 to 9 of each period and pooled by period. Postprandial ruminal fermentation was studied by sampling the fermentors hourly for 5h after the 0800h feeding on d 9 of each period. The total fermentation contents were harvested at the end of the period for estimations of bacterial protein synthesis. Replacing corn starch with dry glycerol linearly increased the proportions of propionate and valerate at the expense of acetate in the fermentation fluid measured daily or for the first 5h after feeding. Replacing corn starch with dry glycerol also linearly increased the digestibility of dietary neutral detergent fiber without a change on the flow or efficiency of bacterial protein synthesis during continuous culture. Results indicate that glycerol as a dry product can replace dietary starch as corn starch at a level of up to 8% of DM in the diet without negatively affecting ruminal fermentation and digestibility during continuous culture.

Alfalfa cut at sundown and harvested as baleage increases bacterial protein synthesis in late-lactation dairy cows

Alfalfa (Medicago sativa L.) cut at sundown (p.m.) has been shown to have a greater concentration of total nonstructural carbohydrates (TNC) than when cut at sunup (a.m.). Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in a crossover design (24-d periods) to investigate the effects of alfalfa cutting time on digestibility and omasal flow of nutrients. Alfalfa was cut at sundown or sunup, field-wilted, and harvested as baleage (530±15.0g of dry matter/kg of fresh matter). The difference in TNC concentration between p.m. and a.m. alfalfa within each pair of bales fed daily during the 10 d of data and sample collection varied from −10 to 50 g/kg of dry matter. Each pair of bales was fed for ad libitum intake to cows once daily with no concentrate. During the 3 d of omasal sampling, intake (+0.8kg/d) and omasal flow of organic matter (OM; +0.42kg/d) tended to be greater when cows were fed p.m. vs. a.m. alfalfa, but no differences were found for ruminal and postruminal digestion of this nutrient. Similarly, N apparently digested ruminally and postruminally did not differ when feeding p.m. vs. a.m. alfalfa. However, N truly digested in the rumen, as a proportion of N intake, was significantly greater in cows fed p.m. (79%) vs. a.m. alfalfa (74%), thus suggesting that longer wilting time of alfalfa cut at sundown increased forage proteolysis. Supply of rumen-degradable protein did not change (2,716 g/d) when averaged across treatments, whereas omasal flow of non-NH3 nonbacterial N was significantly decreased (−29 g/d) when feeding p.m. vs. a.m. alfalfa. Omasal flow of total bacterial non-NH3-N (NAN) increased (+21 g/d) significantly when cows were fed p.m. vs. a.m. alfalfa possibly because bacteria from cows fed p.m. alfalfa captured significantly more NH3 than those from cows fed a.m. alfalfa. Therefore, greater availability of fermentable energy as TNC appears to increase the capacity of microbes to uptake NH3-N and convert it to microbial protein. Enhanced OM intake can also explain the observed increase in bacterial protein synthesis with p.m. alfalfa. Efficiency of bacterial protein synthesis, expressed on a fermented OM basis or as grams of bacterial NAN per gram of rumen-degradable N, did not differ between p.m. and a.m. alfalfa. Conversely, bacterial efficiency, as grams of bacterial NAN per gram of N intake, was significantly increased when cows were fed p.m. baleage. No significant difference between forage treatments was found for the omasal flow of total AA from omasal true digesta, suggesting no benefit of daytime cutting management on the passage of total AA to the lower gastrointestinal tract. Enhancing energy intake and TNC concentration of alfalfa by shifting forage cutting from sunup to sundown increased protein synthesis and NH3 uptake by ruminal bacteria indicating an improvement in N utilization.

Fermentation characteristics and microbial growth promoted by diets including two‐phase olive cake in continuous fermenters

Two-phase olive cake (2POC) is the by-product obtained from the so called 'two-phase' procedure to extract olive oil by mechanical methods. After the mechanical extraction the 2POC is dried and most of the remaining oil extracted by chemical means. The production of the crude by-product may reach more than 4 millions t/year in Spain (MAPA, 2003), most of it in areas (Southeast) with shortage of pastures and conventional feeds for ruminants. Six continuous fermenters, inoculated with ruminal liquor from wethers or goats, were fed lucerne hay (LH); LH plus a concentrate including dried two-phase olive cake (LHCO) and; diet LHCO added with polyethylene glycol (LHCOP). The highest pH values and ammonia N (NH(3)-N) output were found in fermenters fed diet LH (6.19 and 6.35 for pH, and 53.7 and 68.9 mg NH(3)N/day, respectively, in fermentes inoculated with rumen liquor from sheep and goats) without differences due to the inoculum origin. The digestibility of carbohydrates (CHO) was affected (p < 0.001) by inoculum (67.0 and 58.8%, respectively, for goats and wethers) the lowest values being for diet LHCO (53.2 and 57.0% with inoculum from wethers and goats, respectively). The main volatile fatty acid (VFA) was acetic acid with higher (p < 0.01) values in fermenters with inoculum from goats than from wethers (80.2 and 63.0 mmol/day respectively). The efficiency of bacterial protein synthesis (EBS) was not different (p > 0.05) with inoculum from wethers and goats [26.4 and 28.1 and 35.2 and 33.5 g bacterial N/kg digested CHO, respectively, obtained by using diamino pimelic acid (DAPA) and purine bases (PB) as microbial markers]. The lowest (p < 0.05) values were found in fermenters fed diets LHCOP and LH, estimated, respectively, from DAPA and PB (21.9 and 29.0 g bacterial N/kg digested CHO). The substitution of a part of lucerne hay by a concentrate including dried 2POC does not seem to cause important differences in efficiency of VFA production. Results concerning bacterial protein synthesis are not so clear since values estimated from DAPA and PB did not show similar trends. Neither inoculum origin nor PEG had important effects on fermentation characteristics. The DAPA could be an adequate marker in continuous fermenters, with comparative purposes, as protozoa are not present and, estimated protein synthesis values are similar to those obtained in vivo with similar diets using urinary excretion of PD (Yáñez Ruiz et al., 2004b). Further research is needed to state the optimal proportion of 2POC in practical diets for ruminants at both maintenance and production stages.

Efficiency of microbial protein synthesis on red clover and ryegrass silages supplemented with barley by rumen simulation technique (RUSITEC)

Bacterial protein supply from the rumen is frequently low in animals fed on silage-based diets, partially because of the lack of rumen available sources of energy. An in vitro experiment was designed to determine the optimum rate of inclusion of rolled barley to optimise rumen efficiency of bacterial protein synthesis ( E BPS) of diets comprising a typical ryegrass silage (GR; crude protein (CP) = 139 g/kg dry matter (DM); water soluble carbohydrates (WSC) = 71 g/kg DM; NH 3–N = 133 g/kg N; pH 4.23) or red clover silage (RC; CP = 168 g/kg DM; WSC = 28 g/kg DM; NH 3–N = 80 g/kg N; pH 4.12). Both silages were mixed with increasing proportions of barley grain (0, 150, 300 and 450 g/kg DM). Treatments were tested using the rumen simulation technique (RUSITEC), replicated in three independent 10-day incubation periods (blocks). Artificial saliva was infused at a rate of 0.5 ml/min, and on day 4 of incubation 15NH 4SO 4 was added as a microbial marker. Ammonia–N and pH of the effluent were above 50 mg/l and 6.6, respectively, in all treatments and at all time points measured. Inclusion of barley grain reduced the effluent concentrations of acetic, propionic and total volatile fatty acids ( P ≤ 0.06). Apparent digestibilities of DM (DM AD) and organic matter (OM AD) did not differ between RC or GR silages, but RC had lower ( P < 0.001) neutral and acid detergent fibre digestibilities than GR silage. The effluent concentrations of acetic, propionic, butyric and total volatile fatty acids from GR was higher ( P < 0.05) than from RC diets. Inclusion of barley grain linearly ( P < 0.06) reduced the effluent acetic, propionic and total volatile fatty acid concentrations, but increased DM AD, OM AD and efficiency of bacterial dry matter synthesis ( E BDMS). However, there was no clear response in E BPS from GR silage supplemented with barley, but in RC silage, E BPS increased up to a barley inclusion rate of 300 g/kg DM. It is concluded that rumen microorganisms reduced the amount of substrate fermented in correspondence with the increment in barley grain. The E BPS increased in RC silage by adding barley at rates of up to 300 g/kg DM. Conversely, the addition of barley to GR silage had no apparent effect on E BPS.

Carbohydrate fermentation and nitrogen metabolism of a finishing beef diet by ruminal microbes in continuous cultures as affected by ethoxyquin and(or) supplementation of monensin and tylosin

Long-term feedlot studies have shown positive effects (i.e., improved ADG and reduced morbidity and mortality) of dietary supplementation with ethoxyquin (AGRADO). This may be due to improving the antioxidant capacity at the ruminal, postruminal, or postabsorption levels. This study was designed to investigate the role of ethoxyquin at the rumen level. A finishing diet (12.5% CP; DM basis) was formulated to contain (on a DM basis) 77.5% flaked corn, 10% corn cobs, 10% protein/vitamin/mineral supplement, and 2.5% tallow. In a randomized complete block design experiment, the treatments were arranged as a 2 x 2 factorial. The main factors were two ethoxyquin treatments (without or with 150 ppm) and two monensin/tylosin treatments (without or with monensin and tylosin at 0.0028 and 0.0014% of dietary DM, respectively). Eight dual-flow, continuous culture fermenters were used in two experimental periods (blocks; 8 d each with 5 d for adjustment and 3 d for sample collection) to allow for four replications for each treatment. No interactions (P > 0.05) were detected for any of the measurements evaluated. Therefore, results of the main factors were summarized. Ethoxyquin supplementation improved (P < 0.05) true digestibility of OM (from 38.8 to 45.0%) but it did not alter (P > 0.05) concentrations of total VFA (averaging 131 mM) or acetate (averaging 58.8 mM). Ethoxyquin decreased (P < 0.05) propionate concentration from 51.1 to 42.4 mM and increased (P < 0.05) butyrate concentration from 18.4 to 22.9 mM. Digestion of total nonstructural carbohydrates was not altered (P > 0.05) by the treatments and averaged 86%. With the exception of increased (P < 0.05) concentration of propionate (from 42.0 to 51.5 mM) and decreased (P < 0.05) concentration of butyrate (from 25.9 to 16.3 mM), no effects (P > 0.05) were detected for monensin/tylosin. Ruminal N metabolism, including efficiency of bacterial protein synthesis (averaging 21.2 g N/kg OM truly digested), was not affected (P > 0.05) by the treatments. Results suggest positive effects of ethoxyquin on ruminal digestion of OM and unique changes in VFA production.

Sites of Digestion and Bacterial Protein Synthesis in Dairy Heifers Fed Fresh Oats with or Without Corn or Barley Grain

Six Holstein-Friesian heifers fitted with ruminal, duodenal, and ileal cannulas were used in a replicated 3 × 3 Latin square to study the effects of partial replacement [1:1 dry matter (DM) basis] of fresh winter oats (WO) by ground corn (C) or barley (B) on digestion and bacterial protein synthesis. Supplemented diets contained 24% starch, and all diets were fed indoors at 2.5% of body weight (DM basis). Ruminal and total tract digestibilities of organic matter and neutral detergent fiber were similar for all treatments. Ruminal and total tract starch digestibility was similar for C and B diets. Nitrogen intake was greater for WO than for supplemented diets. However, duodenal flows of nonammonia N and bacterial N did not differ among treatments. The efficiency of bacterial protein synthesis was similar for the three diets, suggesting that the fermentation of high quality fresh forage DM provided sufficient energy for the microorganisms in the rumen. Ruminal ammonia-N concentration was greater for WO than for supplemented diets, and for C than for B diet. Ruminal fluid pH and concentrations of total volatile fatty acid were not different among diets, but concentration of acetate was higher and that of propionate was lower for WO than for supplemented diets and for C than for B diet. Supplementation of WO with barley rather than with corn decreased C2:C3 ratio without affecting fiber digestion. Supplements increased N utilization relative to N intake but did not increase duodenal nonammonia N flow.

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.

Avoparcin and monensin effects on the digestion of nutrients in dairy cows fed a mixed diet

An in vivo study was carried out to evaluate the effect of avoparcin on fiber, starch and nitrogen (N) digestion compared with monensin. Three dairy lactating cows with ruminal, duodenal and ileal cannulas were used in a 3 × 3 Latin square design. Cows were fed three diets; the control diet had no additive, and the others contained 33 ppm of either avoparcin or monensin-sodium. There were no treatment effects on ruminal pH and total volatile fatty acid levels; molar proportion of propionate tended to be higher (27.9–29.9 vs. 23.7%) and of butyrate tended to be lower (9.9–12.9 vs. 15.4%) for the antibiotic-supplemented diets. Also, both additives decreased ruminal ammonia N concentration (77.2–105.6 vs. 164.1 mg L−1). The supply of avoparcin or monensin reduced the ruminal breakdown of fiber (36.1 and 37.1 vs. 45.9%) starch (57.4 and 54.7 vs. 63.6%), and dietary N (59.5 and 53.6 vs. 67.3%); efficiency of bacterial protein synthesis was unchanged. Passage of bacterial N to the small intestine was not modified; flows of fiber, starch, nonammonia N and dietary N were improved by the both additives. In comparison with the control, monensin caused a greater quantity of glucose (2100 vs. 1500 g d−1) and total amino acids (AA) (1381 vs. 1047 g d−1) to be digested in the small intestine; avoparcin had a less pronounced effect on the intestinal absorption of glucose (1700 g d−1) and AA (1152 g d−1). Only monensin increased the plasma glucose levels (3.6 vs. 3.1 mM). Both additives did not affect total tract digestibilities of organic matter, fiber, starch, and N. Postruminal digestion of fiber was greater (16.0 vs. 7.3%) for antibiotic-supplemented diets, compensating for the lower forestomach digestion. In comparison with monensin dietary avoparcin had a less pronounced effect on the alteration of nutrient digestion. Key words: Avoparcin, monensin, rumen, intestines, amino acids, digestion, cattle

Digestion in the Rumen and Total Tract of Forage-Based Diets with Starch or Dextrose Supplements Fed to Holstein Heifers1,2

Three diets were fed to six cannulated heifers in a replicated 3 × 3 Latin square design. Diets were a high forage control, a high forage diet with dextrose (5.6% of DM), and a medium concentrate (39.7% of DM) diet. Diets contained 13.3% CP and 1% NaHCO3 and were fed as a TMR twice daily. Mean ruminal pH (6.47), glucose concentration (.55mM), and reducing sugar concentration (.64mM) in heifers were similar across diets. Rate of orchardgrass NDF digestion in situ was faster for heifers fed the dextrose than for those fed the medium concentrate diet, but both were similar to that for heifers fed the control diet. Heifers fed the medium concentrate and dextrose diets had faster ruminal particulate fractional passage rates than those fed the control diet. True ruminal and apparent total tract digestion of OM and NDF were similar among diets, but ruminal NDF digestion tended to be higher with the control than with the medium concentrate diet. Total NAN and bacterial N flow to the duodenum and efficiency of bacterial protein synthesis in the rumen were greater with the medium concentrate diet than with the control and dextrose diets. The results were consistent with others that demonstrated that factors related to nonstructural carbohydrates in the diet other than just low ruminal pH affect ruminal fiber digestion; however, these results were not as strong as those of our previous in vitro work.

Evidence for a high efficiency of bacterial protein synthesis in the digestive tract of adult sows fed supplements of fibrous feedstuffs

Two experiments with adult sows were carried out to obtain data on the fermentation of wheat bran and alfalfa meal and on the effects of these feedstuffs on nitrogen turnover and bacterial protein synthesis. Wheat bran was provided at levels of 0 g, 225 g and 675 g per day and alfalfa meal was given in amounts of 0 g, 575 g and 1150 g per day both in addition to a basal diet covering maintenance requirements. Each treatment was carried out in eight replicates. Both supplements significantly impaired the digestibility of different carbohydrate fractions. The level of supply, however, had no effect on the partial digestibility of these carbohydrates as incorporated in wheat bran and alfalfa meal. A proportion of 40–46% of the non-starch polysaccharides from wheat bran and alfalfa meal was degraded which is similar to the level previously observed with purified cellulose. Fecal nitrogen composition was only slightly affected by the supplements, whereas the excretion of all nitrogenous fractions increased. With alfalfa meal, the fecal N per gram of N intake significantly increased at a cost of urinary N. Bacterial protein excretion per 100 g of fermented matter was 13 g, 20 g and 28 g for the basal diet alone, for wheat bran and for alfalfa meal, respectively. The values obtained with the supplements fall within the range estimated for the efficiency of microbial protein formation in the rumen of ruminants.

Effects of pectin supplementation on the digestion of different structural carbohydrate fractions and on bacterial nitrogen turnover in the hindgut of adult sows

In two consecutive periods, pectin was supplied at levels of 0 and 334 g dry matter day −1 together with a semi-synthetic basal diet to 12 adult sows weighing 166 ± 17 kg. In addition to the pectin treatments, two different levels of thiamine, 0.66 and 2.57 mg day −1 were applied. Aliquot samples of the completely collected feces were analyzed for proximate principles, detergent fiber fractions and nitrogen fractions. In the urine, nitrogen and allantoin N were determined, while the urea content was measured in blood plasma. The pectin fermentation rate was determined by three different methods so as to account for 94–96% of pectin intake. A slight, non-significant decrease in the digestibilities of all analyzed fiber components of the basal diet occurred with pectin. The apparent digestibility of nitrogen was reduced by more than 20% at an almost constant true N digestibility. The increased fecal nitrogen excretion with pectin caused a reduction in protein retention to zero, and was composed of 82% bacterial nitrogen. The changes in the proteinaceous water-soluble fraction of fecal nitrogen indicated an increase in the excretion of endogenous proteins. Calculation of the content of metabolizable energy, by a standard formula estimated from the digestibilities of the proximate contents, was demonstrated to underestimate the true energy content of pectin severely, as evaluated from energy balance trials (5.9 MJ ME kg −1 instead of 10.5 MJ ME kg −1). This occurred because the additional energy excretion in the form of bacterial protein was incorrectly considered as a genuine metabolic energy loss. The efficiency of bacterial protein synthesis using pectin, as estimated by fecal excretion, was 7.4 g per 100 g of pectin fermented. The thiamine treatments did not affect any of the criteria.

Effects of diets formulated to contain different amounts of rumen non-degradable protein on microbial fermentation and nutrient flow from a continuous culture system

Eight dual flow continuous culture fermenters were used in three experimental periods to evaluate effects of diets formulated to contain different amounts of rumen undegradable protein on microbial fermentation and nutrient flow. Two dietary treatments contained 51% forage (28.5% alfalfa haylage and 22.6% maize silage) and 49% concentrate on a DM basis. The concentrate mix consisted of 28.9% ground maize, 15.9% soyabean meal (SBM) and 2.0% animal fat for the control diet (CTRL), or 30.4% ground maize, 2.3% SBM, 9.0% expeller processed SBM (ES), 3.1% fish meal (FM) and 2.0% animal fat for the low degradable protein diet (ESFM). Dietary energy (1.74 Mcal kg −1), crude protein (CP, 19.2%) neutral detergent fiber (NDF, 28.8%) and acid detergent fiber (ADF, 18.6%) content did not differ between diets. Control and ESFM diets were formulated to contain 68% or 55% rumen degradable protein, respectively. True OM and DM digestion were not affected ( P > 0.05) by dietary treatment. Digestion of NDF (43.1 versus 38.8%, P = 0.07) and ADF (59.3 versus 54.7%, P < 0.05) was lower when fermenters received ESFM rather than CTRL diet. Although total VFA concentration was not affected ( P > 0.05) by dietary treatment, molar proportion (mol per 100 mol) of propionate (29.2 versus 24.2, P < 0.05) was higher, and acetate (48.8 versus 53.8, P < 0.05) and acetate to propionate ratio (2.25 versus 1.70, P < 0.05) lower for the ESFM compared with CTRL. Changes in VFA fermentation patterns were possibly due to fat composition of the protein supplements. Ammonia nitrogen concentration in the effluent, and non-ammonia, dietary and bacterial nitrogen flow from the fermenters were not affected ( P > 0.05) by dietary treatment. Efficiency of bacterial protein synthesis and dietary crude protein degradation were not affected ( P > 0.05) by dietary treatment. Partial replacement of SBM by ES and FM decreased fiber digestion and altered VFA molar proportion in the effluent, but did not reduce ruminal degradation of dietary protein.

Quantification of intraruminal recycling of microbial nitrogen using nitrogen-15.

Studies were done to derive a technique to quantify intraruminal recycling of microbial nonammonia nitrogen (NAN). After dosing 15NH4+ into the rumen, ruminal NH3N and NAN pools were sampled over time for analyses of 15N enrichment. Compartmental analysis of both pools was used to quantify the percentage of microbial NAN that recycles in the rumen. Microbial NAN does not need to be fractionated from total NAN, assuming that only microbial NAN becomes labeled with 15N and that the ratio of microbial NAN:nonmicrobial NAN remains constant over time. Based on the data obtained from eight nonlactating cattle fed 85% corn silage diets at 1.5 to 1.0% BW, percentage of intraruminal recycling of microbial NAN was related to efficiency of bacterial protein synthesis (grams of CP/100 g of OM truly digested) in a curvilinear manner (y = 100 - .073x2). From this function, recycling was predicted to be approximately 75% for dairy cows consuming 50:50 forage:concentrate diets at 3.5% of BW. However, more data are needed to evaluate intraruminal recycling of microbial NAN using this technique under different dietary conditions.

Nitrogen Metabolism in Rumen and Whole Digestive Tract of Lactating Dairy Cows Fed Grass Silage

Effects of wilting of grass prior to ensiling on OM intake, ruminal digestibility, efficiency of bacterial protein synthesis, and amount and composition of duodenal N fraction were examined using four lactating Holstein cows. Direct-cut or wilted grass silages were fed for ad libitum intake and supplemented with 5.0 or 5.3kg of concentrate, respectively. Milk yield was 18.1 and 21.2 kg/d with direct-cut versus wilted silage, and milk protein and fat contents were 2.63 and 4.60% with direct-cut versus 2.75 and 4.27% with wilted silage, respectively. Wilting of the grass (from 17 to 38% DM) increased OM intake but had no effect on ruminal digestibility. Total N flow and amounts of different AA in proximal duodenum were increased, and the difference was principally of bacterial origin. The efficiency of bacterial protein synthesis in rumen was related to dilution rate of liquid phase and to the time devoted to ruminating. These results indicate that the passage of bacterial protein to the lower digestive tract is a key factor for improving the assimilation of the soluble N fraction of grass silage and that this phenomenon is related to chewing activity.

Effet de l'extrusion de la féverole (Vicia faba) sur les flux intestinaux d'azote et d'amidon chez la vache laitière en production

Four mature lactating Holstein cows fitted with permanent ruminal, duodenal and ileal cannulae were used to study the effect of extrusion at 195 degrees C of beans (Vicia faba cv Castel) on organic matter (OM), nitrogen (N) and starch degradation in the rumen and their flow to and absorption from the small intestine. The test protein sources, raw beans (RB) and extruded beans (EB), provided about 45% of the dietary protein. The diets were composed of 23.1% beans, 56.2% corn silage, 10.1% corn grain and 10.7% Italian rye-grass hay on a DM basis; the diets were isocaloric (4.5 Mcal/kg of DM) and isonitrogenous (14% of DM). Cr-EDTA, YbCl3 and purines were used as liquid, particulate and bacterial markers respectively. Extruding the beans did not influence intraruminal pH (6.6), ammonia-N (99 mg/l) and volatile fatty acids (97 mM/l) concentrations. Apparent digestibility in total tract of energy, OM, N and starch were not affected with inclusion of EB instead of RB, the corresponding mean values were: 66, 68, 64 and 95% of intake. Apparent ruminal digestion of OM, starch and N in the forestomach were 39, 58 and 52% for diets containing RB and 38, 72 and 45% for EB diets; efficiency of bacterial protein synthesis (gN/kg organic matter truly digested in the stomach) was higher for EN diets compared with RN diets (25 vs 22). Eating diets including EB increased non-ammonia-N, bacterial-N and dietary-N flows (g/d) to the duodenum compared with diets containing RB: 409 vs 366, 216 vs 194 and 193 vs 172 respectively; while starch flow was reduced (1.5 vs 2.2 kg/d) and OM flow was unchanged (9.8 kg/d). Apparent digestion from the small intestine (g/d) of nonammonia-N, bacterial-N and dietary-N were higher for EB diets: 268 vs 229, 181 vs 160 and 87 vs 69 respectively; meanwhile, starch digestion decreased (975 vs 1,612). The PDIA, PDIN and PDIE contents (g/kg of DM) of the RB were 33, 175 and 127 respectively; the corresponding values after extrusion were: 58, 147 and 178.

Cellulose fermentation capacity of the hindgut and nitrogen turnover in the hindgut of sows as evaluated by oral and intracecal supply of purified cellulose

Adult sows fed a constant amount of a basal diet received purified cellulose either orally at levels of 0 and 475 g/animal.d (Experiment 1) or intracecally at levels of 0, 285, 570 and 855 g/animal.d (Experiment 2). Each experiment consisted of subsequent periods of faeces and urine collection with the animals re-allocated to the treatments each time. With that, a total of 36 observations on each parameter was achieved. The faecal samples were analyzed for the contents of organic matter, cell wall carbohydrates and various nitrogen fractions such as bacterial N and undigested dietary N. Furthermore, N balance, urinary allantoin excretion and plasma urea concentrations were determined. In a preliminary study, the effects of freeze-drying and of shaking of the faecal samples as suspensions with water (in order to release bacteria from fibre) on content and composition of faecal nitrogen had turned out to be reproducible. Cellulose significantly enhanced faecal nitrogen loss whereas N retention was not affected due to the counteraction of urinary N loss. Plasma urea concentration reflected the situation with urinary N. The proportion of undigested dietary N and of water-soluble protein in total faecal N was somewhat increased by cellulose at cost of the bacterial N proportion which accounted for about 72% of total N on average. Urinary allantoin did not respond to the higher bacterial activity in the hindgut in the presence of supplementary cellulose. Cellulose significantly decreased the apparent N digestibility by on average about 3 percentage units per 100 g of supplementary cellulose. True N digestibility was also reduced by cellulose but did not go below 95%. The supplementary cellulose was fermented in the hindgut at similar rates of on average about 60% regardless of the route of administration. The almost 100 g of native cellulose incorporated in the basal diets were lignified by about 20%, and that is why they were fermented at a rate of only about 30%. The rate of fermentation was only slightly decreasing with increasing amounts of supplementary cellulose, and a daily quantity of 564 g (11 g/W0.75) cellulose was fermented on average if the highest level of cellulose was provided. This was within a range exclusively reported for easily-fermentable carbohydrates but was achieved in the case of cellulose only at a consistently higher level of supply. The true efficiency of bacterial protein synthesis was 5.2 g bacterial protein/100 g supplementary cellulose on average. The apparent efficiency was 60% higher averaging 8.4 g bacterial protein/100 g further apparently fermented organic matter.

Digestion ruminale et absorption intestinale des protéines du lupin extrudé chez la vache laitière

Four lactating cows fitted with permanent ruminal, duodenal and ileal cannulae were used to study the effect of extrusion of whole lupin seeds at 195 degrees C (Lupinus albus cv Lublanc) on organic matter (OM) and nitrogen (N) degradation in the rumen and their flow to and absorption from the small intestine. Raw whole lupin seeds (RWLS) and extruded whole lupin seeds (EWLS) were fed in diets containing 15.5% crude protein and composed of 22.6% whole lupin seeds, 56.5% corn silage, 10.2% corn grain and 10.7% Italian ray-grass on a DM basis, supplemented with vitamins and minerals. Chromium ethylenediaminotetraacetic (Cr-EDTA) and ytterbium chloride (YbCl3) were used as liquid and particulate markers respectively, while purines and 15N ammonium sulfate were utilized as bacterial markers. Cows fed EWLS had a similar ruminal ammonia N and volatile fatty acid concentrations and efficiency of bacterial protein synthesis compared to those fed the RWLS diet. Total tract OM and N digestion were not affected by inclusion of EWLS instead of RWLS; the corresponding mean values were 70 and 71%. Apparent degradation of OM and N in the rumen were 44 and 64% for diets containing RWLS, and 40 and 39% for EWLS diets. Feeding diets including EWLS both increased non ammonia N and dietary N flow to the duodenum compared with diets containing RWLS (472 vs 357 g/d) and (263 vs 153 g/d) respectively. Absorption from the small intestine (g/d and % entering) of dietary N was higher for EWLS diets (146 vs 62 g/d; 34 vs 15%). The PDIA, PDIE and PDIN contents (g/kg of DM) of RWLS were 18, 94 and 245 respectively; the corresponding values after extrusion were 145, 220 and 220.