No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Partitioning of Amino Acids Flowing to the Abomasum into Feed, Bacterial, Protozoal, and Endogenous Fractions
Abstract
We partitioned the flow of amino acids (AA) to the abomasum among rumen undegradable protein (RUP) and bacterial, protozoal, and endogenous fractions using four Holstein cows in midlactation that were equipped with ruminal and abomasal cannulas. A 2 x 2 factorial design with four diets, combinations of high or low ruminally degradable organic matter, and rumen degradable protein, was employed. Crude protein (CP) and AA contents of ruminal bacteria and protozoa and abomasal digesta were determined. Equations for the source compositions and in vivo flows of CP and 16 AA were then solved simultaneously with a linear program to estimate the contribution of RUP, bacterial, protozoal, and endogenous CP to AA flows. The flows of RUP and bacterial AA were not affected by diet. Low dietary RDP increased the flow of protozoal AA to the abomasum, but the ruminally degradable organic matter content of the diet did not affect protozoal AA flow. Across diets, RUP, bacterial, protozoal, and endogenous fractions provided 55, 33, 11, and <1% of the CP, and 62, 26, 12, and <1% of the AA that reached the abomasum. The linear program was a useful tool for partitioning AA that flows to the abomasum. The technique may also allow dietary effects on ruminal microbes and the AA profile of protein flowing to the duodenum to be better understood and perhaps manipulated.
... Source: Data from Shabi et al. (2000), Socha et al. (2005) and Ordway et al. (2009). (MP) concept used in protein evaluation systems for dairy cows (Schwab and Broderick, 2017). ...
... Reducing dietary CP is the most significant means by which to increase the efficiency of dietary protein utilization (Sinclair et al., 2014;Broderick, 2018). Some of the recommendations Table 2 Means and standard errors of amino acid (AA) composition (g AA/100 g total AA) in 22 ruminal bacteria and two protozoal species cultured in vitro (Purser and Buechler, 1966), mixed ruminal bacteria from lactating cows (Shabi et al., 2000), or cattle (Sok et al., 2017;Gresner et al., 2021) Days in milk: 174 ± 29 days. Diet was based on corn silage (36% of diet DM), cracked corn or expanded corn (36% of diet DM) and soybean meal (10% of diet DM). ...
... Dry matter intake averaged 16.2 ± 0.6 kg/d. There were no treatment effects on production variables, AA profiles or AA flows to the duodenum (Shabi et al., 2000). ...
This chapter reviews the use of amino acids in dairy nutrition, focusing specifically on enhancing milk protein synthesis and other unique physiological processes essential for optimal health and performance. It begins with some general background to amino acids and dairy nutrition, then goes on to discuss the reduction of dietary crude protein in dairy cow diets. It reviews protein feeding and amino acid balancing as well as the physiological roles of essential amino acids beyond milk protein. A section on methionine, lysine and other essential and non-essential amino acids is also included.
... • Eleven studies that did not examine LAB and PAB separately (Cecava & Parker, 1993;Fessenden et al., 2017Fessenden et al., , 2019Hussein et al., 1995;Jensen et al., 2006;Korhonen et al., 2002aKorhonen et al., , 2002bPutnam et al., 1997;Reynal et al., 2003;Shabi et al., 2000;Yang et al., 2001) and ...
... The data set for the protozoa initially comprised 10 studies and 20 diets, two of which differed only in terms of a lignosulfonate treatment of the soybean meal it contained (Shabi et al., 2000). ...
... A study using 2-aminoethylphosphonic acid (AEPA) as a protozoal marker was excluded (Cockburn & Williams, 1984) because AEPA may also occur in significant concentrations in rumen bacteria and in some feedstuffs (Cockburn & Williams, 1984;Ling & Buttery, 1978). Three other studies, which had drawn conclusions on the contribution of protozoa to TMN flow by means of the AA pattern of bacterial and protozoal protein (Reynal et al., 2003(Reynal et al., , 2005Shabi et al., 2000), were also not included in the data set as validation of this method using a reliable protozoal marker is owing (Reynal et al., 2005). Because the remaining studies did not always contain information on the CP concentration in the diet, the calculations requiring CP were performed with a sub-data set (Table 3). ...
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 (kg0.75) as fixed effects (RMSE = 3.77). With moderate PCO and DMI between 80 and 180 g/kg0.75, 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.
... The supernatant was then discarded and the isolated bacterial pellets were composited by cow and period and frozen at −20°C for later analysis. Rumen protozoa were isolated using a separation funnel according to the procedure described by Shabi et al. (2000). The strained ruminal digesta were mixed with 1 volume of warm 0.9% saline and held in a separation funnel for 1.5 h at 39°C. ...
... The in vitro incubation procedure was carried out according to Tilley and Terry (1963). Fermentations were terminated at 24 h and a crude pellet was isolated from each fermentation tube by high-speed centrifugation (30,000 × g for 20 min at 4°C) according to Shabi et al. (2000). Then, DNA was extracted by repeat bead beating using a PowerMag Soil DNA Isolation Kit (Mo Bio, Carlsbad, CA). ...
... An effect of HMTBA supplementation on MCP flow was not observed in this study, similar to the results of Noftsger et al. (2005) but in contrast to those of Lee et al. (2015). Rumen protozoa were isolated using the separatory funnel method described by Shabi et al. (2000), which may have led to and overestimation of protozoal N in calculation of MCP flow . ...
Four multiparous, lactating Holstein cows (average DIM 169.5 ± 20.5 d), fitted with ruminal and duodenal cannulas, were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments to investigate the effects of 2-hydroxy-4-methylthio-butanoic acid (HMTBA) when fed with diets differing in metabolizable protein (MP) supply and equal levels of crude protein on milk production and composition, rumen microbial activity, duodenal protein flow, and rumen bacterial community composition in vivo and in vitro. Experimental periods were 28 d in length. Cows were housed in individual tie stalls and were randomly assigned to 4 dietary treatments: low MP or high MP, supplemented with or without 25 g of HMTBA, which was top-dressed once daily at 0930 h. No interactions were observed between HMTBA and level of dietary MP, with the exception of ruminal acetate-to-propionate ratio. Milk yield was not affected by treatment and averaged 23.8 ± 2.06 kg/d. There was a tendency for increased milk protein percent in cows receiving low MP diets, averaging 3.30 ± 0.09% and 3.21 ± 0.09% for low MP and high MP, respectively. The total-tract apparent digestibility of organic matter, neutral detergent fiber, and nitrogen were greater in cows consuming the low MP diet. Rumen pH was lower in cows consuming high MP diets as well as in those consuming HMTBA. Rumen ammonia concentrations tended to be greater in cows consuming HMTBA, and volatile fatty acid concentrations were greater in cows consuming HMTBA. Duodenal dry matter flow, nitrogen flow, and microbial nitrogen flow did not differ between treatments. The bacterial community structure of cows receiving HMTBA was not affected at the phylum level. The relative abundance of bacterial phyla in vivo differed when compared with in vitro conditions for Firmicutes, Bacteroidetes, Proteobacteria, TM7, Tenericutes, Spirochaetes, SR1, and Verrucomicrobia.
... When the type of bacteria (i.e., FAB or PAB) was not clearly specified in the manuscript, we evaluated the procedure described in the original manuscript. For most of the studies, it corresponded to FAB, but 5 studies were discarded because a mixture of FAB and PAB had been reported ( Cecava and Parker, 1993;Cunningham et al., 1994;Larsen et al., 2000;Shabi et al., 2000;Jensen et al., 2006). Concentrations of Met and Cys were only kept for studies specifying that the sulfur groups had been protected before hydrolysis; other AA of these studies were kept in the database. ...
... In agreement with our data, Lys concentration was consistently higher by more than 50% in protozoa than in bacteria ( Martin et al., 1996;Volden et al., 1999;Korhonen et al., 2002). For other studies reporting composition of protozoa and FAB ( Williams and Dinusson, 1973;Rahnema and Theurer, 1986) or the composition of protozoa and a mixture of FAB and PAB ( Shabi et al., 2000;Jensen et al., 2006), although no statistics were made to delineate significant differences, Lys concentration was consistently higher in protozoa than in bacteria. Protozoa metabolize the diaminopimelic acid in bacterial cell walls to Lys ( Martin et al., 1996), but the high Lys might also indicate accumulation for some as yet unknown reason. ...
... The major point herein was to determine the ratio of FAB-to-PAB-to-protozoa Journal of Dairy Science Vol. 100 No. 7, 2017 in the duodenal protein flow to calculate composite concentration. Because of problems with overlap of various other marker approaches when trying to quantify protozoal N outflow ( Firkins et al., 1998Firkins et al., , 2007), the literature was searched for dairy studies in which bacterial and protozoal flow were derived using independent marker approaches ( Robinson et al., 1996;Shabi et al., 2000;Reynal et al., 2003Sylvester et al., 2005;Castillo-Lopez et al., 2013). After weighting the data for the inverse of standard error of the means, none of the approaches used (quantitative PCR, phosphatidylcholine, or optimization of AA profiles) were different (P = 0.85). ...
Because microbial crude protein (MCP) constitutes more than 50% of the protein digested in cattle, its AA composition is needed to adequately estimate AA supply. Our objective was to update the AA contributions of the rumen microbial AA flowing to the duodenum using only studies from cattle, differentiating between fluid-associated bacteria (FAB), particle-associated bacteria (PAB), and protozoa, based on published literature (53, 16, and 18 treatment means were used for each type of microorganism, respectively). In addition, Cys and Met reported concentrations were retained only when an adequate protection of the sulfur groups was performed before the acid hydrolysis. The total AA (or true protein) fraction represented 82.4% of CP in bacteria. For 10 AA, including 4 essential AA, the AA composition differed between protozoa and bacteria. The most noticeable differences were a 45% lower Lys concentration and 40% higher Ala concentration in bacteria than in protozoa. Differences between FAB and PAB were less pronounced than differences between bacteria and protozoa. Assuming 33% FAB, 50% PAB, and 17% of protozoa in MCP duodenal flow, the updated concentrations of AA would decrease supply estimates of Met, Thr, and Val originating from MCP and increase those of Lys and Phe by 5 to 10% compared with those calculated using the FAB composition reported previously. Therefore, inclusion of the contribution of PAB and protozoa to the duodenal MCP flow is needed to adequately estimate AA supply from microbial origin when a factorial method is used to estimate duodenal AA flow. Furthermore, acknowledging the fact that hydrolysis of 1 kg of true microbial protein yields 1.16 kg of free AA substantially increases the estimates of AA supply from MCP.
... To extend this to amino acids supply, we would need to estimate the AA profile of the endogenous protein and then calculate supply and digestibility. There are several data sets available where these estimates have been made and can easily be adopted in the CNCPS (Shabi et al., 2000;Ouellet et al., 2002;and Marini et al. (2008). It will require a reworking of how maintenance requirements are calculated and a change in the number of protein pools that are available to the animal. ...
... The CNCPS does not have a protozoa pool within the rumen submodel, however it is now known that from 5% to at least 20% of the total AA flows from the rumen are from the protozoa (Shabi et al., 2000;Karnati et al., 2007). The CNCPS currently calculates that the protozoa consume 20% of the estimated bacterial yield, thus the Ymax estimation is reduced from 0.5 g of bacteria per g of carbohydrate per hour to 0.4 g. ...
... It is important to recognize that protozoa have a different AA profile, especially with respect to methionine and lysine. The methionine content of protozoa is lower than that of bacteria (24.0 vs 28.4 g/kg of total AA, whereas the lysine content of protozoa is significantly greater than bacteria (121.4 vs 90.3 g/kg total AA) (Shabi et al., 2000). This suggests that under certain formulation conditions, if protozoa were included in the prediction of AA flow, lysine might not be as limiting an AA provided protozoal growth and escape made up a significant portion of the MP supply. ...
... To extend this to amino acids supply, we would need to estimate the AA profile of the endogenous protein and then calculate supply and digestibility. There are several data sets available where these estimates have been made and can easily be adopted in the CNCPS (Shabi et al., 2000; Ouellet et al., 2002; and Marini et al. (2008). It will require a reworking of how maintenance requirements are calculated and a change in the number of protein pools that are available to the animal. ...
... The CNCPS does not have a protozoa pool within the rumen submodel, however it is now known that from 5% to at least 20% of the total AA flows from the rumen are from the protozoa (Shabi et al., 2000; Sylvester, et al. 2005; Karnati et al., 2007). The CNCPS currently calculates that the protozoa consume 20% of the estimated bacterial yield, thus the Ymax estimation is reduced from 0.5 g of bacteria per g of carbohydrate per hour to 0.4 g. ...
... It is important to recognize that protozoa have a different AA profile, especially with respect to methionine and lysine. The methionine content of protozoa is lower than that of bacteria (24.0 vs 28.4 g/kg of total AA, whereas the lysine content of protozoa is significantly greater than bacteria (121.4 vs 90.3 g/kg total AA) (Shabi et al., 2000). This suggests that under certain formulation conditions, if protozoa were included in the prediction of AA flow, lysine might not be as limiting an AA provided protozoal growth and escape made up a significant portion of the MP supply. ...
... Intentional ignoring of protozoa has been inappropriately justified based on results using indirect procedures, the combination of which appears to compound to underestimate duodenal flow of protozoal N (Firkins et al., 1987a). In contrast, indirect methods not relying on these potentially biased procedures tend to provide generally higher protozoal N flows (Steinhour et al., 1982;Shabi et al., 2000). ...
... Besides capturing protozoa for direct quantification purposes, filtration has been used to provide a more representative sample of protozoa to be used for marker studies (Martin et al., 1994). Classical approaches used in many published reports used gravitational separation of protozoal cells from flocculating ruminal fluid primarily using separatory funnels (Firkins et al., 1987a;Shabi et al., 2000) or centrifugation (Punia and Leibholz, 1994;Ivan et al., 2000). These procedures could have significant amounts of contamination of bacterial matter (Sharp et al., 1998;Volden et al., 1999;Sylvester et al., 2004), so the accuracy of a direct protozoal marker could be decreased by the procedures used to harvest a reference protozoal fraction. ...
... Although some researchers used separatory funnels (Firkins et al., 1987a;Shabi et al., 2000) or similar techniques to separate sedimented protozoa, we chose to centrifuge at slow speed (Punia and Leibholz, 1994;Ivan et al., 2000) to reduce user subjectivity. Moreover, in our preliminary studies, sedimented protozoa that were aspirated with a Pasteur pipette from the bottom of an Erlenmeyer flask were biased toward isotrichid protozoa, particularly if the sample was taken shortly after feeding the cow (data not shown). ...
We have recently developed a real-time polymerase chain reaction (PCR) assay to quantify copies of the genes encoding protozoal 18S rRNA. The assay includes procedures for isolating and concentrating protozoal cells from the rumen for use as a standard to convert 18S rRNA gene copies to a biomass basis. The current objectives were to 1) determine the degree of reduction of bacterial contamination in the protozoal standard, 2) determine if protozoal standards derived from ruminal fluid are appropriate for predicting duodenal flows, and 3) evaluate the assay's determined values for protozoal N in the rumen and flowing to the duodenum compared with independent measurements. Our protozoal collection method reduced non-associated bacterial contamination by 33-fold, the contamination of which could otherwise significantly bias RNA (microbial marker) and N percentages of concentrated protozoal fractions. Based on denaturing gradient gel electrophoresis, the use of protozoal cells isolated from ruminal fluid appears appropriate for use in quantitative assays determining protozoal N flow postruminally. Using real-time PCR, protozoal N was determined to be 4.8 and 12.7% of the rumen microbial N pool and 5.9 and 11.9% of the duodenal flow of microbial N on diets containing low (16%) or high (21%) forage neutral detergent fiber, respectively, which were comparable with independent measures and expectations.
... Thus, no single ratio of marker:protein would be appropriate to obtain an absolute determination of total microbial protein synthesized in the rumen. Shabi et al. (2000) used linear programming based on the AA composition patterns of isolated bacteria and protozoa, plus dietary and endogenous protein, to estimate the relative contributions from these four sources to total AA flow from the rumen. A mathematical approach of this type may not be influenced by factors altering purine:protein ratio, such as microbial growth rate (Broderick and Merchen, 1992), and may be more reliable for estimating AA contributions from each fraction. ...
... Proportions of nutrients of bacterial, protozoal, and dietary origin in omasal digesta also were estimated using a linear programming approach. The Solver function of Excel (Windows Small Business, Microsoft, Redland, WA) was used to apportion flows of NAN and TAAN among RUP, bacteria, and protozoa from each cow in each period using Standard Simplex linear programming with the nonnegative constraint option, using the linear programming method described by Shabi et al. (2000). ...
... The NRC (2001) assigned intestinal digestibilities of 93, 93, 80, and 94% for the RUP fractions of SSBM, ESBM, BM, and CGM, respectively. These estimates of omasal AA flow (Table 4), the AA concentrations in the diets (Table 2), and in isolated bacteria and protozoa (Table 3) also were used in linear programming analysis (Shabi et al., 2000) to estimate proportions of TAAN and NAN derived from RUP and contributed by ruminal microbes. ...
Ten ruminally cannulated lactating Holstein cows that were part of a larger trial studying the effects of feeding different proteins on milk production were used in a replicated 5 x 5 Latin square to quantify flows of microbial and rumen-undegradable protein (RUP) in omasal digesta. Cows were fed total mixed rations containing (dry matter basis) 44% corn silage, 22% alfalfa silage, 2% urea, and 31% concentrate. The basal diet contained 31% high-moisture corn; equal N from one of four protein supplements was added to the other diets at the expense of corn: 9% solvent soybean meal (SSBM), 10% expeller soybean meal (ESBM), 5.5% blood meal (BM), and 7% corn gluten meal (CGM). Omasal sampling was used to quantify total AA N (TAAN) and nonammonia N (NAN) flows from the rumen. Estimates of RUP were made from differences between total and microbial N flows, including a correction for RUP in the basal diet. Modifying a spectrophotometric assay improved total purine recovery from isolated bacteria and omasal samples and gave estimates of microbial TAAN and NAN flows that were similar to a standard HPLC method. Linear programming, based on AA patterns of the diet and isolated omasal bacteria and ruminal protozoa, appeared to overestimate microbial TAAN and NAN flows compared to the purine assays. Yields of microbial TAAN and NAN determined using any method was not affected by diet and averaged 32 to 35 g NAN per kilogram of organic matter truly digested in the rumen. On average, National Research Council (NRC) equations underpredicted microbial N flows by 152 g/d (vs. HPLC), 168 g/d (vs. spectrophotometry), and 244 g/d (vs. linear programming). Estimates of RUP (means from the HPLC and spectrophotometric methods) were: SSBM, 27%, ESBM, 45%, BM, 60%, and CGM, 73%. Except for CGM, RUP values averaged about 20 percentage units lower than those reported by the NRC.
... Microbial protein synthesized in the rumen is the most important source of amino acids at the duodenum (Maeng and Baldwin 1976;Boghum et al. 2006). Researchers have found that the chemical composition of liquid-associated bacteria (LAB), solid associated bacteria (SAB) and protozoa is different (Martin et al. 1994;Shabi et al. 2000;Boghum et al. 2006). Therefore, one can presume that an alteration in the relative proportion of the microbes would eventually have an impact on the chemical composition of the whole microbial fraction and finally on the actual microbial nutrients flux into the abomasum. ...
... It has been found that the amino acid profiles of the microbial portion flowing out of the rumen differ, and these can be influenced by dietary changes. Bacteria seemed to have higher concentrations of alanine, glycine, phenylalanine, threonine and valine and lower concentrations of aspartic acid, glutamic acid, histidine, isoleucine, and lysine than protozoa (Shabi et al. 2000). Boghum et al. (2006) found that some diets that were composed of identical feedstuffs in varying proportions did not result in different amino acid profiles of reference microbes, liquid associated and solid associated microbes, while diets with similar nutrient and energy content, but based on different ingredients, showed significant differences. ...
Castro-Montoya, J. M., Makkar, H. P. S. and Becker, K. 2011. Chemical composition of rumen microbial fraction and fermentation parameters as affected by tannins and saponins using an in vitro rumen fermentation system. Can. J. Anim. Sci. 91: 433–448. Post-rumen chemical composition of the microbial fraction is one of the factors that determines the nutrients absorbed and available for maintenance and production of the animal. The hypothesis was that tannins and saponins alter chemical composition of rumen microbes and fermentation parameters in the rumen. Purified quebracho, mimosa, chestnut and sumach tannins; and quillaja and gypsophilla saponins were incubated with 380 mg of substrate (hay:concentrate 70:30 wt/wt) for 24 h in an in vitro gas production system at concentrations from 0.25 to 1.25 mg mL⁻¹. Saponins increased N and reduced sugar contents of the liquid-associated microbes. The ratio of crude protein to purine bases significantly increased on adding sumach and chestnut tannins and decreased on the addition of quebracho and mimosa tannins. Quebracho, mimosa and chestnut tannins reduced total short-chain fatty acid production. The acetate:propionate ratio decreased for all additives. Results suggest that in vitro (a) depending on the source and the concentration, tannins would have an effect on the nitrogen and sugar contents of the liquid associated microbes, (b) saponins are likely to increase N and reduce sugar contents of rumen liquid associated microbes, and (c) estimation of microbial protein synthesis based on purine bases may lead to under- or over-estimations in the presence of tannins and saponins. In vivo studies are required to validate these results.
... Recently, linear programming was used to partition N flowing to the duodenum into feed, bacteria, protozoa, and endogenous fractions (Shabi et al., 2000; Reynal et al., 2003). Using the same approach, we have calculated the relative proportions of SAB and LAB in duodenal content (Vlaeminck et al., 2006). ...
... Hence, variation in relative proportions of SAB and LAB could largely influence estimates of rumen microbial synthesis when either SAB or LAB marker:N ratios are used for calculations. Recently, linear programming was used to partition N flowing to the duodenum into feed, bacteria, protozoa, and endogenous fractions (Shabi et al., 2000; Reynal et al., 2003). Using the same approach, we have calculated the relative proportions of SAB and LAB in duodenal content (Vlaeminck et al., 2006). ...
The aim of this research was to examine to what extent variation in the relative proportions of solid- (SAB) and liquid-associated rumen bacteria (LAB) in duodenal bacteria have an impact on the estimation of duodenal flowofbacterialN.Forthis,fourdairycowswerefeddietsvaryinginforage:concentrate ratio (80:20, 65:35, 50:50 and 35:65). SAB and LAB were separated from rumen contents four h after the morning feeding. Adenine, cytosine and odd and branched-chain fatty acids were determined both in SAB and LAB and used to estimate bacterial N flow. Bacterial N flowswerealsocalculated using a SAB:LAB ratio in duodenal bacteria, as estimated from the odd and branched-chain fatty acid pattern. Compared with calculations based on the estimated SAB:LAB ratio, estimations based on SAB or LAB only as a bacterial reference on average over- and underestimated bacterial N flowby37and55gN/d,respectively(P<0.05)whencytosineoradeninewereusedasbacterialmarker. In contrast, due to the small differences in the OBCFA:N ratio between SAB and LAB, these differences were less than 15 g/d when OBCFA were used as bacterial marker. The results suggest that, depending on the marker used, changes in the proportions of SAB and LAB can have a substantial impact on estimated duodenal flow of bacterial N.
... ticleassociated bacteria and protozoa should be accounted for when estimating microbial flows. Although the omasal sampling technique allows for the isolation and measurement of flow of bacteria associated with liquid and particle phases, lack of specific markers precludes accurate assessment of the protozoal contribution to microbial protein flow. Shabi et al. (2000) used linear programming based on the AA profiles of isolated bacteria and protozoa, plus that of dietary protein and endogenous protein, to estimate the relative contributions from these 4 sources to total AA flow from the rumen. An approach of this type may not be influenced by factors altering marker:protein ratio and could be more re ...
... Microbial NAN flow from the rumen was estimated based on the excretion of PD using the equation of Vagnoni et al. (1997) and the purine:N ratio in FAB plus PAB isolates in their proportions flowing at the omasal canal. Proportions of N fractions of bacterial, protozoal, and dietary origin in omasal digesta were estimated with the AA profile approach proposed by Shabi et al. (2000) using the Standard Linear program in Premium Solver for Excel 2000 as described by. The estimated proportions, together with digesta flow measurements, were used to compute flows of NAN fractions from FAB, PAB, protozoa, and dietary origin at the omasal canal. ...
Eight ruminally cannulated lactating cows from a study on the effects of dietary rumen degraded protein (RDP) on production and N metabolism were used to compare 15N, total purines, amino acid (AA) profiles, and urinary excretion of purine derivatives (PD) as microbial markers for quantifying the flow of microbial protein at the omasal canal. Dietary RDP was gradually decreased by replacing solvent soybean meal and urea with lignosulfonate-treated soybean meal. The purine metabolites xanthine and hypoxanthine were present in digesta and microbial samples and were assumed to be of microbial origin. The sum of the purines and their metabolites (adenine, guanine, xanthine, and hypoxanthine) were defined as total purines (TP) and used as a microbial marker. Decreasing dietary RDP from 13.2 to 10.6% of dry matter (DM) reduced microbial nonammonia N (NAN) flows estimated using TP (from 415 to 369 g/d), 15N (from 470 to 384 g/d), AA profiles (from 392 to 311 g/d), and PD (from 436 to 271 g/d). Averaged across diets, microbial NAN flows were highest when estimated using TP and 15N (398 and 429 g/d), lowest when using PD (305 g/d), and intermediate when using AA profiles (360 g/d) as microbial markers. Correlation coefficients between 15N and TP for fluid-associated bacteria, particle-associated bacteria, and total microbial NAN flows were 0.38, 0.85, and 0.69, respectively. When TP was used as the microbial marker, ruminal escape of dietary NAN was not affected by replacing solvent soybean meal with lignosulfonate-treated soybean meal in the diets. The direction and extent of response of dietary and microbial NAN flow to dietary treatments were similar when estimated using 15N, AA profiles, and PD, and were in agreement with previously published data and National Research Council predictions. Microbial and dietary NAN flows from the rumen estimated using 15N appeared to be more accurate and precise than the other markers. Caution is required when interpreting results obtained using TP as the microbial marker.
... Rumen microbial metabolic pathways and metabolites were different than in cattle, and mainly, amino acids were also confirmed later in yaks (Zhao et al., 2022). A total of 11% of amino acids absorbed by the small intestine were derived from protozoa (Shabi et al., 2000), and in the absence of nitrogen in the rumen, protozoa and bacteria synthesized and stored polysaccharides and used them when sufficient nitrogen was available (Dewhurst et al., 2000). Therefore, further research is needed to determine the function of protozoa in yaks during the MCP synthesis. ...
Livestock on the Qinghai-Tibetan Plateau is of great importance for the livelihood of the local inhabitants and the ecosystem of the plateau. The natural, harsh environment has shaped the adaptations of local livestock while providing them with requisite eco-services. Over time, unique genes and metabolic mechanisms (nitrogen and energy) have evolved which enabled the yaks to adapt morphologically and physiologically to the Qinghai-Tibetan Plateau. The rumen microbiota has also co-evolved with the host and contributed to the host's adaptation to the environment. Understanding the complex linkages between the rumen microbiota, the host, and the environment is essential to optimizing the rumen function to meet the growing demands for animal products while minimizing the environmental impact of ruminant production. However, little is known about the mechanisms of host-rumen microbiome-environment linkages and how they ultimately benefit the animal in adapting to the environment. In this review, we pieced together the yak's adaptation to the Qinghai-Tibetan Plateau ecosystem by summarizing the natural selection and nutritional features of yaks and integrating the key aspects of its rumen microbiome with the host metabolic efficiency and homeostasis. We found that this homeostasis results in higher feed digestibility, higher rumen microbial protein production, higher short-chain fatty acid (SCFA) concentrations, and lower methane emissions in yaks when compared with other low-altitude ruminants. The rumen microbiome forms a multi-synergistic relationship among the rumen microbiota services, their communities, genes, and enzymes. The rumen microbial proteins and SCFAs act as precursors that directly impact the milk composition or adipose accumulation, improving the milk or meat quality, resulting in a higher protein and fat content in yak milk and a higher percentage of protein and abundant fatty acids in yak meat when compared to dairy cow or cattle. The hierarchical interactions between the climate, forage, rumen microorganisms, and host genes have reshaped the animal's survival and performance. In this review, an integrating and interactive understanding of the host-rumen microbiome environment was established. The understanding of these concepts is valuable for agriculture and our environment. It also contributes to a better understanding of microbial ecology and evolution in anaerobic ecosystems and the host-environment linkages to improve animal production.
... In line with Martineau et al. (2023a), the site of sampling was categorized as duodenal (sampling from the abomasum or the duodenum) or omasal (sampling from the reticulum or the omasum). Digesta was sampled from the abomasum in Mabjeesh et al. (1997) and Shabi et al. (2000), and was sampled from the reticulum in Naadland et al. (2016). Overall, the data set included 279 treatment means from 71 duodenal studies and 82 treatment means from 24 omasal studies before screening for outlying treatments. ...
... As such, some researchers have taken alternative approaches to estimate protozoal contribution to the microbial N pool. Using a linear programming approach, Shabi et al. (2000) estimated protozoal N to account for 7 to 19% of microbial N flow. This was a result similar to that estimated by Steinhour et al. (1982) using a differential 15 N enrichment approach, although many assumptions were made pertaining to pool size and turnover in that study. ...
The objective of this study was to evaluate the effect of a fermentation by-product on rumen function, microbial yield, and composition and flows of nutrients from the rumen in high-producing lactating dairy cattle. Eight ruminally cannulated multiparous Holstein cows averaging (mean ± standard deviation) 60 ± 10 d in milk and 637 ± 38 kg of body weight were randomly assigned to 1 of 2 treatment sequences in a switchback design. Treatment diets contained (dry matter basis) 44% corn silage, 13% alfalfa silage, 12% ground corn, and 31% protein premix, containing either a control mix of urea and wheat middlings (CON) or a commercial fermentation by-product meal (Fermenten, Arm and Hammer Animal Nutrition, Princeton, NJ) at 3% diet inclusion rate (EXP). The trial consisted of three 28-d experimental periods, where each period consisted of 21 d of diet adaptation and 7 d of data and sample collection. A triple-marker technique and double-labeled ¹⁵N¹⁵N-urea were used to were used to measure protozoal, bacterial, and nonmicrobial omasal flow of AA. Rumen pool sizes and omasal flows were used to determine digestion parameters, including fractional rates of carbohydrate digestion, microbial growth, and yield of microbial biomass per gram of degraded substrate. Fermentation by-product inclusion in EXP diets increased microbial N and amino acid N content in microbes relative to microbes from CON cows fed the urea control. Microbial AA profile did not differ between diets. Daily omasal flows of AA were increased in EXP cows as a result of decreased degradation of feed protein. The inclusion of the fermentation by-product increased nonmicrobial AA flow in cows fed EXP versus CON. Average protozoal contribution to microbial N flow was 16.8%, yet protozoa accounted for 21% of the microbial AA flow, with a range of 8 to 46% for individual AA. Cows in this study maintained an average rumen pool size of 320 g of microbial N, and bacterial and protozoal pools were estimated at 4 different theoretical levels of selective protozoa retention. Fractional growth rate of all microbes was estimated to be 0.069 h⁻¹, with a yield of 0.44 g of microbial biomass per gram of carbohydrate degraded. Results indicated that fermentation by-product can increase omasal flow of AA while maintaining adequate rumen N available for microbial growth and protein synthesis. Simulations from a developmental version of the Cornell Net Carbohydrate and Protein System indicated strong agreement between predicted and observed values, with some areas key for improvement in AA flow and bacterial versus protozoal N partitioning.
... The supply of AA reaching the SI determines whether or not the protein requirement of the ruminant is met (Shabi et al., 2000). In this way, we can infer that converting dietary CP to body protein is influenced by AA profile that reaches the SI, as well as AA digestibility. ...
The objectives of this study were to evaluate the effect of reducing dietary CP contents on (1) total and partial nutrient digestion and nitrogen balance, and (2) on microbial crude protein (MCP) synthesis and true MCP digestibility in the small intestine obtained with ¹⁵N and purine bases (PB) in beef cattle. Eight bulls (4 Nellore and 4 Crossbred Angus × Nellore) cannulated in the rumen and ileum were distributed in duplicated 4 4 Latin squares. The diets consisted of increasing CP contents: 100, 120, or 140 g CP/kg DM offered ad libitum, and restricted intake diet (RI) with 120 g CP/kg DM. The experiment lasted four 17 d periods, with 10 d for adaptation to diets and another seven for data collection. Omasal digesta flow was obtained using Co-EDTA and indigestible NDF (iNDF) as markers and to estimate ileal digesta flow only iNDF was used. From d 11 to 17 of each experimental period, ruminal infusions of Co-EDTA (5.0 g/d) and ¹⁵N (7.03 g of ammonium sulfate enriched with 10% of ¹⁵N atoms) were performed. There was no effect of CP contents (linear effect P = 0.55 and quadratic effect P = 0.11) on ruminal OM digestibility. Intake of CP linearly increased (P < 0.01) with greater dietary CP. The NH3-N (P < 0.01) and urinary N excretion (P < 0.01) increased in response to dietary CP, while retained N increased linearly (P = 0.03). Liquid-associated bacteria (LAB) in the omasum had greater N content (P < 0.05) in relation to the particle-associated bacteria (PAB). There was no difference between LAB and PAB (P = 0.12) for ¹⁵N:¹⁴N ratio. The ¹⁵N:¹⁴N ratio was greater (P < 0.01) in RI animals in relation to those fed at voluntary intake. Microbial CP had a quadratic tendency (P = 0.09) in response to CP increase. Microbial efficiency (expressed in relation to apparent ruminally degradable OM and true ruminally degradable OM) had a quadratic tendency (P = 0.07 and P =0.08, respectively) to CP increasing and were numerically greatest at 120 g CP/kg DM. The adjusted equations for estimating true intestinal digestibility of MCP (Y1) and total CP (Y2) were respectively: Y1 = -16.724(SEM = 40.06) + 0.86X(SEM = 0.05), and Y2 = - 43.81(SEM = 49.19) + 0.75X(SEM = 0.05). It was concluded that diets with 120 g/kg of CP optimize the microbial synthesis and efficiency and ruminal apNDF digestibility, resulting in a better use of N compounds in the rumen. The PB technique can be used as an alternative to the ¹⁵N to estimate microbial synthesis.
... The supply of AA reaching the SI determines whether or not the protein requirement of the ruminant is met (Shabi et al., 2000). In this way, we can infer that converting dietary CP to body protein is influenced by AA profile that reaches the SI, as well as AA digestibility. ...
The objective of this study was to determine the apparent and true intestinal digestibility of total and individual AA, and to estimate the efficiency of whole-body AA retention from individual and total absorbed AA. Four Nellore animals (241.3 kg initial BW) and four crossbred Angus x Nellore (263.4 kg initial BW), cannulated in rumen and ileum were randomly allocated in two 4 × 4 Latin squares. The experiment lasted four 17 d periods, with 10 d for adaptation to diets and another seven for data collection. The diets consisted of increasing CP levels: 100, 120, or 140 g/kg of DM offered ad libitum, and restricted intake diet (RI) with 120 g CP/kg DM (Exp. 1). In Exp. 2, forty-four bulls, (22 Nellore and 22 crossbred F1 Angus x Nellore) with 8 months and initial shrunk BW (SBW) 215.0 ± 15.0 kg (Nellore = 208.0 ± 12.78 kg; Angus x Nellore = 221.9±14.16 kg) were used. Eight of those animals were slaughtered at the beginning of the experiment. The remaining 36 bulls were allocated in a completely randomized design with six replicates, in a 2 (genetic groups) 3 (CP contents) factorial scheme. The amount of essential AA (EAA) and non-essential AA (NEAA) reaching the small intestine (SI) increased linearly (P < 0.05) in response to CP content. The apparent digestibility of EAA was not affected (P > 0.05) by CP content, with exception for histidine (P = 0.07, linear effect), leucine (P = 0.01, linear effect) and methionine (P = 0.05, linear effect). Differences existed among AA when compared the apparent digestibility of NEAA. The apparent digestibility of alanine (P = 0.05), aspartic acid (P = 0.07), glutamic acid (P = 0.02), glycine (P = 0.05), proline (P = 0.02) and serine (P = 0.04) responded quadratically to CP content increase. However, the apparent digestibility of cystine and tyrosine were not affected (P > 0.05) by increasing dietary CP. The true intestinal digestibility of total, essential, non-essential AA, lysine and methionine were 75.0, 77.0, 74.0, 77.0 and 86%, respectively. The true intestinal digestibility of total microbial AA was 80%. The efficiency of utilization of total AA for whole-body protein deposition was 40%. The efficiency of utilization of lysine and methionine was 37 and 58%, respectively. It was concluded that the AA flow to the omasum increase in response to dietary CP content. In addition, there are differences among AA in the efficiency that they are used by beef cattle.
... However, the observation that PEDS decreased the concentration of NH 3 -N in the current study suggested an increase in the efficiency of MCP synthesis reflected by the increased MN and MOEEF with the addition of PEDS (Table 5). MCP contributes significantly to the CP requirement for ruminants and supplies an average of 59% (range from 34-89%) of non-ammonia nitrogen that passes to the duodenum [41]. Plenty of studies about natural plant extract enhancing the synthesis efficiency and production of MCP were reported in recent years [42,43], while the literature, ether in vitro or in vivo, about PEDS used in this field was absent. ...
The objective of this study was to evaluate the effects of supplementation of phytoecdysteroids (PEDS) extracted from Cyanotis arachnoidea on rumen fermentation, enzymes activity and microbial efficiency in a dual flow continuous-culture system. A single-factor experimental design was used with twelve fermenters in 4 groups with 3 replicates each. Fermenters were incubated for a total of 7 days that included first 4 days for adaptation and last 3 days for sampling. PEDS was added at levels of zero (as control), 5, 10, and 15 mg/g of the substrate (DM). The results showed that increasing supplementation levels of PEDS resulted in incremental digestibility of dry matter (DMD) (quadratic, P = 0.001) and organic matter (OMD) (quadratic, P = 0.031), but unchanged digestibility of neutral detergent fiber (NDFD), crude protein (CPD) and acid detergent acid (ADFD). As supplementation levels of PEDS increased, there were decreased response in the concentration of ammonia nitrogen (NH3-N) (linear, P = 0.015) and increased response in molar proportions of butyrate (linear, P = 0.004), but unchanged response in total volatile fatty acid (TVFA) and the molar proportion of acetate and propionate, respectively. Increasing PEDS supplementation levels decreased the ratio of acetate to propionate (linear, P = 0.038), suggesting an alteration of rumen fermentation pattern occurring due to PEDS supplementation in the diet. Supplementation of PEDS significantly increased activities of glutamate dehydrogenase (quadratic, P = 0.001), alanine dehydrogenase (quadratic, P = 0.004), glutamate synthase (linear, P = 0.038), glutamine synthetase (quadratic, P = 0.011), respectively. There were no discernible differences in the activity of carboxymethyl cellulose (CMCase), xylanase and protease regardless of the treatments. The daily production of microbial nitrogen (linear, P = 0.002) and microbial efficiency (MOEEF) (linear, P = 0.001) increased linearly as supplementation levels of PEDS increased. The decreased response of fluid NH3-N and the increased response of MN indicated that PEDS positively increased the synthesis of microbial proteins.
... Moreover, it has to be reminded that the AA profiles in the present study only referred to the bacterial fraction. Although bacterial AA contribute the majority of microbial AA flow in vivo the contribution of protozoa has to be considered (Shabi et al. 2000), because the AA profile of protozoa leaving the rumen was shown to be different from that of bacteria (Martin et al. 1996, Volden et al. 1999, Jensen et al. 2006). ...
... DOBOS 2005). Allgemein erfolgt die Bereitstellung von Protein aber in größerem Umfang über das mikrobielle Protein (BEEVER 1993;MUSCATO et al. 1983;NOLAN 1993;FIRKINS 1996;WALLACE et al. 1997b;BRODERICK 2006) und erst dann über nicht abgebautes Futterprotein (MUSCATO et al. 1983;SHABI et al. 2000). Darüber hinaus tragen abgeschilferte Zellen, wiederkäuereigene Verdauungsenzyme sowie mit dem Speichel sezernierter Harnstoff und Speichelmucine zur Versorgung der Mikroorganismen im Pansen bzw. ...
... Owens and Zinn 1988). However, protozoa are selectively retained within the rumen (Punia et al. 1992), contribute only 11% to the abomasal digesta CP flow (Shabi et al. 2000) and their total nucleic acid content is only slightly higher than that of bacteria (6.8 mg versus 6.1 mg/100 mg; Czerkawski 1976). Moreover, although gram-positive bacteria such as Streptococcus bovis likely proliferated in response to glucose infusion (Russel and Hino 1985) and praecaecal digestibility of their protein is lower than that of gram-negative bacteria (Wallace 1983), the effects of this proliferation on praecaecal MCP digestibility from mixed microbial matter are considered to be small (Wallace 1983). ...
This study investigated the response of urinary purine derivatives (PD) excretion to increasing levels of intraruminal glucose infusion to evaluate how well this indicator reflects induced changes in microbial crude protein flow. Four rumen-cannulated heifers (482 ± 25 kg body weight) were fed at maintenance energy level with a basal diet (on fresh matter basis) of 4 kg/d hay, 1.5 kg/d concentrate and 60 g/d minerals in two equal meals. The trial comprised a control period (Control I) without glucose infusion followed by four consecutive periods in which all animals received 125 g, 250 g, 500 g or 1000 g/d of glucose, respectively. For this, daily dosages of glucose and urea (90 g/d during all periods) were divided into three portions that were dissolved in water and directly administered into the rumen during morning and afternoon feedings and once during noon. After the highest glucose dosage, a second control period was carried out (Control II). Urinary PD excretion increased with glucose infusion of 125 g/d (71.4 mmol/d) and 1000 g/d (74.2 mmol/d) over the level at Control I (53.9 mmol/d (standard error of the mean (SEM) 3.4; p = 0.012). After withdrawing glucose infusion, PD excretion (79.0 mmol/d) did not return to Control I level (p = 0.001). In contrast, faecal nitrogen (N) excretions linearly increased with incremental glucose infusion (p < 0.001) from 33.9 g/d at Control I to 39.7 g/d (SEM 0.5) at 1000 g/d of glucose and were similar in Control I and II (p = 0.086). The contradicting responses in the excretions of faecal N and urinary PD to increasing glucose infusions highlight the limited accuracy of the PD excretion as a non-invasive indicator when incremental dosages of rapidly fermentable carbohydrates are supplied.
... Ruminal protozoal pellets were isolated using a separation funnel according to the procedure described by Shabi et al. (2000). Briefly, the strained ruminal digesta were mixed with one volume of warm 0.9% saline and held in a separation funnel for 1.5 h at 398C. ...
Castillo-Lopez, E., Klopfenstein, T. J., Fernando, S. C. and Kononoff, P. J. 2014. Effect of dried distillers’ grains and solubles when replacing corn or soybean meal on rumen microbial growth in vitro as measured using DNA as a microbial marker. Can. J. Anim. Sci. 94: 349–356. The objectives were to evaluate the use of rDNA markers to measure the effects of dried distillers’ grains with solubles (DDGS) and the potential treatment×time interaction on microbial crude protein (MCP) synthesis in vitro and secondly to measure the contribution of yeast based protein originating from DDGS. Treatments were: (1) CONT, control with no DDGS, but with alfalfa hay, corn silage, ground corn (GC) and soybean meal (SBM) included at 25% (DM basis); (2) LOWCORN, 20% DDGS (DM basis) replacing GC; (3) LOWSBM, 20% DDGS (DM basis) replacing SBM; and (4) LOWCORNSBM, 20% DDGS (DM basis) replacing 10% GC and 10% SBM. Treatments (0.5 g) were incubated in 50 mL of inoculum in duplicate. At 0, 4, 16, 32, 48 and 96 h of fermentation total DNA was extracted from each treatment and MCP was measured using rDNA markers. The sum of bacterial crude protein (BCP) and protozoal crude protein (PCP) was considered as MCP. Data were analyzed as a completely randomized design. The treatment×time interaction was tested and the SLICE option was included to evaluate the effect of treatment at each fermentation time point. There was a tendency to a treatment×time interaction (P=0.07) for MCP. Specifically, at 16 h, LOWCORNSBM yielded greater (P<0.05) MCP compared to either CONT or LOWCORN with estimates of 68.5, 33.8 and 23.3±8.9 mg g–1 DM, for LOWCORNSBM, CONT and LOWCORN, respectively. At 48 h, however, LOWCORN yielded greater MCP (P<0.05) compared with LOWSBM with estimates of 72.2 and 32.5±8.9 mg g–1 DM, for LOWCORN and LOWSBM, respectively. Yeast crude protein (YCP) was not affected (P=0.21) and averaged 0.04±0.02 mg g–1 of substrate (DM basis). Overall, rDNA markers were effective for quantifying MCP, but further research on the methodology is needed. With DDGS inclusion, MCP was maintained; however, yeast cells were extensively degraded during fermentation.
... Mathematical approaches taking AA composition of each fraction into account estimated EN values varying from <10 g/kg to 320 g/kg of total N reaching the abomasum (Shabi et al, 2000). ...
... Protozoa numbers showed no differences among the treatments (Figure 3). The variations of the protozoa numbers was not sufficiently changed to affect the microbial protein synthesis in this study as it was described in the previous study (Jouany and Ushida, 1999;Shabi et al., 2000). And it is generally considered that a steady number of protozoa reflects a steady state of fermentation in a fermenter (Merry et al., 1987) although a criticism (Blake and Sterm, 1988) in that a rapid turnover rate of a fermenter would not maintain a proper number of protozoal poulations exists. ...
A rumen simulated continuous culture (RSCC) system was used to study the influence of supplementation of the three different types of protein sources such as urea, casein and soy protein on rumen microbial synthesis in terms of rumen microbial synchronization. The urea treatment showed the highest pH value. Ammonia nitrogen concentration was rapidly increased after feeding and not significantly different in the urea treatment (13.53 mg/100 ml). Protozoa numbers were not significantly different for soy protein and casein treatment compared to urea treatments during incubation. The average concentration of total VFA (mMol) was not detected with significant difference among treatments, but iso-butyrate production showed the highest for soy protein treatment among treatments (p
... Protozoa are capable of degrading fibrous and nonfibrous CHO (NFC) (Williams and Withers, 1991), and bacteria are their main supply of protein. The contribution of protozoa to the supply of protein to the small intestine is limited, approximately 11% of total CP flow (Shabi et al., 2000) because they are selectively retained in the rumen. The true contribution of protozoa to animal performance is not clear, and there is no consensus on the value of protozoa to ruminants. ...
Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29 g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31 x rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.
... Furthermore , in a second study in lactating cows using an infusion of 15 N-leucine (Ouellet et al., 2005), the endogenous contribution to duodenal N flow averaged 18% when silage was fed, and 20% when hay was offered , representing in this latter case, 5.9 g of N/kg of DMI. In dairy cows, using a mathematical approach including estimates of the composition of AA in each fraction, N from endogenous origin varied between <1% (Shabi et al., 2000) and 32% (Larsen et al., 2001) of total duodenal N flow. With such a high potential contribution, the endogenous fraction can no longer be ignored and needs to be subtracted from measured duodenal flow to determine Journal of Dairy Science Vol. ...
Improving the prediction of milk protein yield relies on knowledge of both protein supply and requirement. Definition of protein/amino acid supply in ruminants is a challenging task, due to feedstuff variety and variability and to the remodeling of nutrient intake by the rumen microflora. The questions arise, therefore, how and where should we measure the real supply of AA in the dairy cow? This review will follow the downstream flow of AA from duodenum to peripheral tissue delivery, with a glance at the efficiency of transfer into milk protein. Duodenal AA flow comprises rumen undegradable feed, microbial protein, and endogenous secretions. Most attention has been directed toward definition of the first two contributions but the latter fraction can represent as much as 20% of duodenal flow. More information is needed on what factors affect its magnitude and overall impact. Once digested, AA are absorbed into the portal vein. The ratio of portal absorption to small intestinal apparent digestion varies among essential AA, from 0.43 (threonine) to 0.76 (phenylalanine), due to the contributions of preduodenal endogenous secretions to the digestive flow, non-reabsorption of endogenous secretions and gut oxidation of AA. Few data are available on these phenomena in dairy cows but the evidence indicates that they alter the profile of AA available for anabolic purposes. Recent comparisons of estimated duodenal flux and measured portal flux have prompted a revisit of the NRC (2001) approach to estimate AA flows at the duodenum. Changes to the model are proposed that yield predictions that better fit the current knowledge of AA metabolism across the gut. After absorption, AA flow first to the liver where substantial and differential net removal occurs, varying from zero for the branched-chain AA to 50% of portal absorption for phenylalanine. This process alters the pattern of net supply to the mammary gland. Overall, intermediary metabolism of AA between the duodenum and the mammary gland biologically explains the decreased efficiency of the transfer of absorbed AA into milk protein as maximal yield is approached. Therefore, variable, rather than fixed, factors for transfer efficiencies must be incorporated into future predictive models.
... However, based on a semi-quantitative examination of band intensities in our DGGE profiles we estimate that there was no more than a 9·2 % difference in the relative distribution of total ciliate biomass between bands in profiles of rumen compared with duodenal samples from the same animal, suggesting the resultant error might also be small. Given the significant contribution of protozoa to the total microbial protein in the rumen, their important role in bacteria predation and their high recycling rates, several methods have been used to estimate the protozoal flow leaving the rumen (Steinhour et al. 1982;Michalowski et al. 1986;Punia et al. 1992;Dijkstra, 1994;Shabi et al. 2000). As noted previously, research in this area is hindered by the lack of an accurate Table 3. Daily intakes and duodenal flows of dry matter, organic matter (OM) and nitrogen and rumen protozoa in steers fed control silage (CS) or high-water-soluble carbohydrates silage (HS) (Mean values and standard errors of the difference) 0·058 Table 4. protozoal marker (Firkins et al. 1998). ...
The present experiment was designed to estimate the quantitative contribution of rumen protozoa to the total N, conjugated linoleic acid (CLA) and vaccenic acid (VA; trans-11-18 : 1) flow to the duodenum of steers fed two silage diets: control silage (CS) and silage high in water-soluble carbohydrates (HS). Protozoal duodenal flows were estimated using a real-time PCR assay to quantify the genes encoding protozoal 18S ribosomal RNA. Denaturing gradient gel electrophoresis was used to confirm that the rumen protozoa populations were similar to the protozoal population flowing to the duodenum. Estimated duodenal flow of protozoal N was 14.2 and 18.2 g/d (P>0.05) for animals fed the CS and HS diets respectively. Protozoal flow thus represented between 12 and 15 % of the total N duodenal flow. In terms of fatty acid flow, protozoa accounted for between 30 and 43 % of the CLA and 40 % of the VA reaching the duodenum. The contribution of protozoa to 16 : 0 and 18 : 0 flows to the duodenum was less than 20 and 10 %, respectively. These results show that the fatty acids within protozoa make up a significant proportion of the CLA and VA reaching the duodenum of ruminants.
Microbial protein contributes about two-thirds of the amino acids absorbed by ruminants. Information on the proportion of bacterial and protozoal N passing to the duodenum would enhance our understanding of the effect of diet not only on microbial protein synthesis but also on the contribution of bacteria and protozoa to duodenal flow of others metabolites of interest. However, differentiation of the duodenal fractions has proven to be difficult because routine procedures cannot separate microbial protein at the duodenum into bacteria and protozoa (Punia et al., 1992). Molecular techniques that use group-specific rRNA-targeted probes may help overcome these problems. The objective of this experiment was to quantify the flow of protozoal N at the duodenum in steers, fed two silage diets differing in water soluble carbohydrates (WSC) content, by real-time PCR using protozoa specific primers.
The effect of dietary dry matter intake (DMI) on endogenous nitrogen (N) flows at different part of the digestive tract of growing lambs was determined using a (15) N isotope dilution technique. Three Kazakh male lambs (30 ± 2.75 kg of body weights and 4 months old, average daily gain 200 g/day) were fitted with ruminal, duodenal and ileal cannulae and raised in metabolic cage individually. The experiment was conducted in a 3 × 3 Latin square design with three lambs, three DMI levels (1100, 920 and 736 g/day respectively) and three periods. Each period lasted 18 days, consisting of 10 days for adaptation, 8 days for the continuous infusion of l-[(15) N]leucine, during which the intestinal flow of N and (15) N enrichment were determined. The total endogenous secretions in the forestomach (Sfs ) were decreased (p = 0.0512) with increased level of DMI. On the contrary, endogenous nitrogen (EN) secretions into the small intestine (Si ) increased (p = 0.0249) significantly with the high level of DMI (HI) group compared with that of low level of DMI (LI). Total absorption from forestomach was reduced (p = 0.0121) with increased level of DMI, whereas total absorption from small intestine for HI group increased (p = 0.0116) significantly compared with that of LI treatment. The real digestibility of N in the rumen accompanied with the increase in feed intake is decreased (p = 0.081). In contrast, there were no effects of DMI level on the computed real digestibility of N across both small intestine and whole tract. The results of this study indicate that the total flows of EN at duodenum may be unaffected by the level of DMI; however, the EN flow at ileal level increased from 12% to 37% with the increase in DMI level, corresponding to 33% of total N flow at ileum.
This article summarizes the current literature as regards metabolizable protein (MP) and essential amino acid (EAA) nutrition of dairy cattle. Emphasis has been placed on research since the publication of the National Research Council Nutrient Requirements of Dairy Cattle, Seventh Revised Edition (2001). Postruminal metabolism of EAA is discussed in terms of the effect on requirements. This article suggests methods for practical application of MP and EAA balance in milking dairy cows.
Sixteen multiparous lactating Holstein cows were used in 2 experiments to evaluate the effects of reduced-fat dried distillers grains with solubles (RFDG) on milk production, rumen fermentation, intestinal microbial N flow, and total-tract nutrient digestibility. In experiment 1, RFDG was fed at 0, 10, 20, or 30% of diet dry matter (DM) to 12 noncannulated Holstein cows (mean ± standard deviation: 89 ± 11 d in milk and 674 ± 68.2 kg of body weight) to determine effects on milk production. In experiment 2, the same diets were fed to 4 ruminally and duodenally cannulated Holstein cows (mean ± standard deviation: 112 ± 41 d in milk; 590 ± 61.14 kg of body weight) to evaluate the effects on rumen fermentation, intestinal flow of microbial N, and total-tract nutrient digestibility. In both experiments, cows were randomly assigned to 4 × 4 Latin squares over 21-d periods. Treatments (DM basis) were (1) control (0% RFDG), (2) 10% RFDG, (3) 20% RFDG, and (4) 30% RFDG. Feed intake and milk yield were recorded daily. In both experiments, milk samples were collected on d 19 to 21 of each period for analysis of milk components. In experiment 2, ruminal pH was measured; samples of rumen fluid, duodenal digesta, and feces were collected on d 18 to 21. Microbial N was estimated by using purines and DNA as microbial markers. Milk yield was not affected by treatment and averaged 34.0 ± 1.29 kg/d and 31.4 ± 2.81 kg/d in experiments 1 and 2, respectively. Percentage of milk protein tended to increase in experiment 1; estimates were 3.08, 3.18, 3.15, and 3.19 ± 0.06% when RFDG increased from 0 to 30% in the diets. However, milk protein concentration was not affected in experiment 2 and averaged 3.02 ± 0.07%. Percentage of milk fat was not affected and averaged 3.66 ± 0.05% and 3.25 ± 0.14% in experiments 1 and 2, respectively. Total ruminal volatile fatty acids and ammonia concentrations were not affected by treatment and averaged 135.18 ± 6.45 mM and 18.66 ± 2.32 mg/dL, respectively. Intestinal microbial N flow was not affected by treatment; however, purines yielded higher estimates of flow compared with DNA markers. When averaged across treatments, intestinal flow of microbial N was 303 and 218 ± 18 g of N/d, using purines and DNA as the markers. Dry matter, organic matter, neutral detergent fiber, and nonfiber carbohydrate digestibility tended to increase with increasing inclusion of RFDG. Results from these experiments indicate that dairy rations can be formulated to include up to 30% RFDG while maintaining lactation performance, volatile fatty acids concentration, and intestinal supply of microbial N.
This study investigated effects of dietary forage particle size (PS) and concentrate level (CL) on fermentation profiles of particle-associated rumen liquid (PARL) and free rumen liquid (FRL), in vitro degradation characteristics and concentration of bacterial mass attached to the solid or fluid rumen digesta phase in dairy cows. The experiment was a 4×4 Latin square design with four late-lactation dairy cows in four 23 day periods. Cows were restrictively fed (17kg dry matter (DM)/d) one of four diets varying in the theoretical PS (6 and 30mm) of grass hay and in the levels (approximately 200 and 550g/kg, DM basis) of a cereal-based concentrate. Proportion of large particles (>6mm) and the content of structural fibre in the diet increased by reducing dietary CL and, particularly, by increasing hay PS. This effect was not reflected by changes in mean total volatile fatty acid concentration or pH in the rumen. However, cows fed high concentrate diets had pH of 5.28 and 5.37 in PARL at 3h after the last meal, when fine or long chopped hay was offered. The low pH may indicate a depression of the capacity of PARL to degrade fibre in vitro. Gas production in vitro of concentrate increased with the high concentrate diet at 12h, suggesting that amylolytic capacity was affected only in early phases of fermentation. In addition, elevating dietary CL appeared to shift ruminal fermentation outputs from propionate to butyrate and valerate. Inclusion of coarsely chopped hay to a high concentrate diet does not appear to bring advantages due to increased structure in restrictively fed dairy cows. In addition, results suggest that the response of pH in PARL is more sensitive to dietary changes (i.e., forage PS and CL) than the response in FRL, and so PARL might be better to evaluate the risk of ruminal disfunction in dairy cows.
The effect of stage of maturity of maize silage on protein metabolism in the gastrointestinal tract of cows was evaluated in an extended 3×3 Latin square experiment. Three multiparous lactating Danish Holstein–Friesian cows fitted with ruminal, duodenal and ileal cannulae were offered maize silage based diets supplemented with soybean meal and a grass-clover hay. The three treatments differed in the dry matter (DM) content of the maize silage, being 257, 350 or 403g/kg. Rumen bacteria were harvested from mixed samples of rumen particles and fluid by sequential centrifugations. Protozoa were harvested by centrifugation after clearance of rumen fluid by flocculation. Synthesis of microbial amino acid nitrogen (AAN) was estimated by the internal markers diaminopimelic acid (DAPA), RNA and total and individual purine bases. Undegraded feed AAN was estimated by the in situ nylon bag method. Further, the origin of duodenal N flow was estimated by use of the amino acid profile (AAP) method. Average DMI was 15.9kg/day. Average N and AAN intakes were 0.457 and 0.329kg/day, respectively. The duodenal flow of N tended to increase from 0.484 to 0.581kg/day with increased maturity of maize (P=0.08). Effective protein degradability (EPD) for the maize silage, the soybean meal and the grass-clover hay was 0.84, 0.71 and 0.57, respectively. Apparent differences were found in the bacterial and protozoal amino acid (AA) profiles (gAA/kgtotalAA), especially for Lys and Ala. Purine profiles (mmol purine/mol total purine) differed for three out of five purines between bacteria and protozoa. The internal RNA marker estimated a microbial AAN net synthesis of 0.165–0.204kg/day. Using the AAP method to estimate the distribution of duodenal protein resulted in the fractions: microbial 0.56, endogenous 0.23 and undegraded feed AAN 0.21. It was not possible to make reasonable estimates using the purine profiles. Average microbial net synthesis of AAN estimated by AAP method (0.198kg/day) and RNA marker method (0.184kg/day), respectively, was comparable. A duodenal AAN flow of 0.112kg/day of undegraded feed protein estimated by in situ degradation was 1.5 times higher than the 0.074kg/day estimated from the AAP method. A substantial amount (0.081kg/day) of endogenous AAN was estimated from the AAP method. The AAP method seemed reliable in this experiment for estimating the supply of protein to duodenum from a number of sources.
The effect of the heat processing on the bioavailability of selenium (Se) in soybean seed containing 324μgSe/kgdry matter (DM), was investigated by measuring the accumulation of Se in rumen bacteria, bodily tissues and whole blood of sheep fed diets containing differently heat processed soybean. Ground soybean seed was subjected to three heat processing treatments; 130°C for 45min (considered the ideal treatment); 150°C for 30min (over-processed treatment) and the untreated soybeans as the control (unprocessed). The acid detergent insoluble nitrogen (ADIN) concentrations of 32, 180 and 13g/kgN in the respective heat treated soybeans were used as indication of relative heat damage inflicted on the protein in the soybeans. Thirty weaned Dohne Merino lambs (ca. 5 months of age, live weight 23.9±0.9kg) were randomly allocated to three diets containing 436g/kg of the differently treated soybean. The diets containing ca. 140μgSe/kgDM, of which 0.95 originated from the soybeans, were fed for 85 days to the lambs after which they were slaughtered. Rumen bacteria from the unprocessed treatment contained a significantly higher concentration of Se (2918μg/kgDM) compared to the over-processed treatment (2188μg/kgDM). The liver, cardiac muscle, wool and whole blood from the ideal treatment contained consistently significantly higher concentrations of Se than either or both of the other two treatments, e.g. the liver contained 1535, 1327 and 1555μgSe/kgDM in the ideal, control and over-processed treatments, respectively, the cardiac muscle 1616, 1527 and 1480μgSe/kgDM, respectively, and in whole blood at the end of the trial 336, 278 and 265μgSe/kg, respectively. It was concluded that the heat processing applied to the organic Se source in this trial affected the bioavailability of the Se, but the heat treatments might not have been sufficiently different to manifest distinct differences in the metabolism of Se in the body.
The objectives of this trial were to determine the rumen undegradable protein (RUP) of dried distillers grains with solubles (DDGS), to compare the estimates of duodenal bacterial crude protein (BCP) flow using diaminopumelic acid (DAPA) or DNA as bacterial markers, and to estimate duodenal protozoal crude protein (PCP) and yeast crude protein (YCP) flow when DDGS are fed. Three crossbred steers fitted with ruminal and double L-shaped duodenal cannulae (average BW 780 ± 137 kg) were used in a 3 treatment, 6 period cross-over design. Animals were housed in individual free stalls and fed twice daily at 0700 and 1900. Diets (DM basis) were 1) CONTROL, 0% DDGS, but with 19.5% corn bran, 20% sorghum silage, 60% brome hay, 0.5% trace minerals and 0.25% urea; 2) LOW DDGS, inclusion of 9.75% DDGS replacing equal percentage of corn bran; 3) HIGH DDGS, inclusion of 19.5% DDGS completely replacing corn bran. Duodenal BCP flow was estimated using DAPA and DNA as bacterial markers. In addition, duodenal PCP and YCP flow were estimated using DNA markers. The value of DDGS RUP as a percent of CP was determined to be 63.0 ± 0.64%. Estimates of duodenal BCP flow using DAPA were 473, 393, 357 ± 78 g/d (P = 0.09) for CONTROL, LOW DDGS and HIGH DDGS, respectively. Estimates of duodenal BCP flow using DNA were 479, 397 and 368 ± 74 g/d (P = 0.14), respectively. Average BCP flow across treatments was unaffected (P = 0.71) by marker type and were 404 and 417 ± 83 g/d for DAPA and DNA markers, respectively. Estimates of duodenal PCP flow were 82, 80 and 78 ± 12 g/d (P = 0.64) for CONTROL, LOW DDGS and HIGH DDGS, respectively. Estimates of duodenal YCP flow were 0.15, 1.94 and 4.80 ± 0.66 g/d (P < 0.01) for CONTROL, LOW DDGS and HIGH DDGS, respectively. Duodenal BCP flow tended to decrease with DDGS inclusion, but estimates were not affected by marker type. In addition, DDGS did not affect duodenal PCP supply and provided small amounts of duodenal YCP. Overall, the value of DDGS RUP determined in this study will contribute to better understand the effect of this byproduct in ruminant nutrition.
In the current Dutch protein evaluation system (the DVE/OEB 1991 system), two characteristics are calculated for each feed: true protein digested in the intestine (DVE) and the rumen degradable protein balance (OEB). Of these, DVE represents the protein value of a feed, while OEB is the difference between the potential microbial protein synthesis (MPS) on the basis of available rumen degradable protein and that on the basis of available rumen degradable energy. DVE can be separated into three components: (i) feed crude protein undegraded in the rumen but digested in the small intestine, (ii) microbial true protein synthesized in the rumen and digested in the small intestine, and (iii) endogenous protein lost in the digestive processes.
Based on new research findings, the DVE/OEB 1991 system has recently been updated to the DVE/OEB 2010 system. More detail and differentiation is included concerning the representation of chemical components in feed, the rumen degradation characteristics of these components, the efficiency of MPS and the fractional passage rates. For each chemical component, the soluble, washout, potentially degradable and truly non-degradable fractions are defined with separate fractional degradation rates. Similarly, fractional passage rates for each of these fractions were identified and partly expressed as a function of fractional degradation rate. Efficiency of MPS is related to the various fractions of the chemical components and their associated fractional passage rates. Only minor changes were made with respect to the amount of DVE required for maintenance and production purposes of the animal. Differences from other current protein evaluation systems, viz. the Cornell Net Carbohydrate and Protein system and the Feed into Milk system, are discussed.
Tämän tutkimuksen tarkoituksena oli määrittää ammoniumtypen, säilörehun liukoisen ja säilörehun liukenemattoman valkuaisen metaboloitumista pötsissä sekä kuvata ammmoniumtypen sekä säilörehun liukoisen ja liukenemattoman fraktion virtauskinetiikkaa alempaan ruoansulatuskanavaan. Koska typen metaboliaa märehtijän elimistössä on tutkittu paljon ja siitä on vakiintuneita käsityksiä, tässä tutkimuksessa keskityttiin metaboliareittien suuruuden arviointiin sekä typen virtausnopeuden estimointiin WinSAAM -ohjelmistolla rakennetun dynaamisen mallin avulla. Koe suoritettiin ajanjaksolla 2.3.-26.4.2002 Maa- ja elintarviketalouden tutkimuskeskuksessa (MTT) Jokioisilla, kotieläintuotannon tutkimusosaston koe-eläintallilla. Koemallina oli 4 x 4 latinalainen neliö, jossa oli neljä eläintä, neljä jaksoa ja neljä koekäsittelyä. Koe-eläiminä olivat neljä usean kerran poikinutta ayrshire-lypsylehmää. Lehmien poikimisesta oli kulunut keskimäärin 68 pv. (± 27 pv). Lehmät saivat 10 kg/pv väkirehuseosta ja hapolla (AIV 2000, 5,4 l/tn) säilöttyä esikuivattua säilörehua vapaasti siten, että jätettä jäi 5-10 %. Typellisten yhdisteiden metaboliareittejä mallinnettaessa havaintoaineistona käytettiin pötsin ammoniumtypen, bakteeritypen, alkueläintypen, liukenemattoman typen ja valkuaisen C-fraktion 15N-rikastumisen perusteella laskettua taustarikastumisen ylittävää poolikokoa. Havaintoaineiston perusteella rakennettiin ammoniumtypen (Malli 1), säilörehun liukoisen ei-ammoniumtypen (SNAN) (Malli 2) ja säilörehun liukenemattoman typen (Malli 3) metaboliareittejä kuvaavat mallit. Malli 1 estimoi ammoniumtypen imeytymisen, ulosvirtauksen ja synteesin bakteeritypeksi erinomaisesti. Alkueläintypen metabolian parametriarvoissa oli enemmän hajontaa kuin ammoniumtypen tai bakteeritypen metabolian parametriarvoissa. Mallin 1 mukaan 38 % ammoniumtypestä imeytyi suoraan pötsin seinämän läpi, 35 % syntetisoitui bakteeritypeksi ja 9 % alkueläintypeksi. Loppuosa (18 %) ammoniumtypestä virtasi nestefaasin mukana satakertaan. Malli 2 estimoi säilörehun SNAN:n metaboitumisen ammonium- ja bakteeritypeksi erinomaisesti. Myös ammoniumtypen metabolia ja bakteeritypen ulosvirtauksen estimointi onnistui erinomaisesti. Malli 2 ei antanut kovin luotettavaa estimaattia alkueläintypen metaboliasta. Mallin 2 mukaan 29 % säilörehun SNAN:stä imeytyi ammoniumtyppenä pötsin seinämän läpi, 10 % virtasi ulos pötsistä ammoniumtypen muodossa, 42 % syntetisoitui bakteeritypeksi ja 7 % alkueläintypeksi. Lisäksi 13 % SNAN:stä ohitti pötsin hajoamatta. Malli 3 estimoi typen metaboliareiteille erittäin tarkat parametriarvot. Tässä mallissa myös alkueläinten metabolialle saatiin luotettavat parametriarvot. Mallin 3 mukaan 57 % säilörehun liukenemattomasta typestä ohitti pötsin hajoamatta, 24 % syntetisoitui bakteeritypeksi ja 18 % alkueläintypeksi. Nurmisäilörehuun perustuvalla dieetillä hyvin suuri osuus satakertaan virtaavasta mikrobivalkuaisesta on peräisin ei-ammoniumtyppi -lähteistä, eli liukenemattomasta rehuvalkuaisesta, aminohapoista ja peptideistä. Koska lyhyt- ja pitkäketjuisten peptidien osuus SNAN fraktiosta on suuri ja koska jopa 13 % säilörehun SNAN fraktiosta voi ohittaa pötsin hajoamatta, on liukoisten typpifraktioiden ja varsinkin peptidien rooli pötsin typpimetaboliassa hyvin merkittävä.
The effect of dietary methionine (Met) levels on endogenous N and amino acids (AA) flows at different part of the digestive tract of growing goats was determined using a (15)N isotope dilution technique. Three goats (25 ± 2.5 kg) were fitted with the ruminal, duodenal and ileal cannulae and allocated to three dietary treatments in a 3 × 3 Latin square design. The dietary treatments consisted of a total mixed ration containing three levels of Met (0.15%, 0.25% and 0.35%) respectively. It was found that at 0.15% Met level, the lowest flow in endogenous N and total AA at the duodenum and ileum occurred. The endogenous N secretion contributed to 26% and 23% of the duodenal and ileal total N flows, respectively, and the proportions were not affected by the dietary Met levels. The duodenal and ileal flows of endogenous total AA were 11.1, 11.8, 11.3 g/d and 2.9, 3.9, 4.1 g/d respectively. The average real digestibility of N was 65%, 87% and 95% in the forestomach, intestine and whole digestive tract respectively.
Abstract: Manipulation of the fermentation of the feeds by the microorganisms in the fore stomach of cattle (rumen) offers a potential approach to minimize waste excretion. However, the conventional evaluation of digestibility of feeds does not describe the microbial mechanisms involved in ruminal digestion. Examining microbial diversity using culture-independent techniques allows greater understanding of the function of complex microbial ecosystems such as the rumen. For the first set of experiments, ruminal and omasal samples were obtained from cows supplemented with different sources of methionine (Met). The objectives in this set of experiments were to study how Met supplementation affected microbial populations in the rumen and if omasal sampling provided a representative sample of ruminal bacteria. Neither the protozoal counts nor the denaturing gradient gel electrophoresis (DGGE) banding patterns derived from protozoa were different among the dietary treatments or for ruminal vs. omasal samples. As revealed by DGGE, bacterial populations clustered by treatments in ruminal and in omasal samples. The next experiments were performed in dual flow continuous culture fermenters to study the interaction between ruminal protozoa, methanogens and eubacteria in a controlled environment. We used microbial inhibitors to selectively suppress different functional groups of microbes in the presence or absence of protozoa. The fermenters were fed either no additive, 5% animal-vegetable, monensin, or bromoethanesulfonate (BES, 250 uM). For the defaunated sub-period, total N flow and digestibilities of NDF and OM were significantly higher and ammonia concentration was lower. Protozoal counts were not different between treatments. Defaunation did not affect total VFA production but decreased the acetate: propionate ratio. Biohydrogenation was impaired in the defaunated fermenters but the flow of cis-9 trans-11 conjugated linoleic acid was unaffected by defaunation or by treatments other than added fat. Defaunation and BES changed methanogen populations despite not decreasing methane production. Monensin did not affect methanogen populations but tended to decrease methane. Defaunation changed eubacterial populations, but the effect of treatments were harder to ascertain. In conclusion, the culture-independent methods allowed us assess the changes in microbial populations in the rumen and in continuous culture. Our modified continuous culture system allowed us assess the changes in microbial populations in the rumen and in continuous culture. Our modified continuous culture system retained a diverse protozoal population, allowing us to study the interaction between ruminal protozoa, methanogens and eubacteria in a controlled environment. 2.59 MB Title from first page of PDF file. Thesis (Ph. D.)--Ohio State University, 2006. Includes bibliographical references (p. 104-114). Available online via OhioLINK's ETD Center System requirements: World Wide Web browser and PDF viewer.
Twelve Angus crossbred cattle (eight heifers and four steers; average initial BW = 594 +/- 44.4 kg) fitted with ruminal and duodenal cannulas and fed restricted amounts of forage plus a ruminally undegradable protein (RUP) supplement were used in a triplicated 4 x 4 Latin square design experiment to determine intestinal supply of essential AA. Cattle were fed four different levels of chopped (2.54 cm) bromegrass hay (11.4% CP, 57% NDF; OM basis): 30, 55, 80, or 105% of the forage intake required for maintenance. Cattle fed below maintenance were given specified quantities of a RUP supplement (6.8% porcine blood meal, 24.5% hydrolyzed feather meal, and 68.7% menhaden fish meal; DM basis) designed to provide duodenal essential AA flow equal to that of cattle fed forage at 105% of maintenance. Experimental periods lasted 21 d (17 d of adaptation and 4 d of sampling). Total OM intake and duodenal OM flow increased linearly (P < 0.001) as cattle consumed more forage; however, OM truly digested in the rumen (% of intake) did not change (P = 0.43) as intake increased. True ruminal N degradation (% of intake) tended (P = 0.07) to increase linearly, and true ruminal N degradation (g/d) decreased quadratically (P = 0.02) as intake increased from 30 to 105%. Duodenal N flow was equal (P = 0.33) across intake levels, even though microbial N flow increased linearly (P < 0.001) as forage OM intake increased. Total and individual essential AA intake decreased (cubic; P < 0.001) as forage intake increased because the supply of nonammonia, nonmicrobial N flow from RUP was decreased (linear; P < 0.001) by design. Total duodenal flow of essential AA did not differ (P = 0.39) across these levels of forage intake. Although the profile of essential AA reaching the duodenum differed (P < or = 0.02) for all 10 essential AA, the range of each essential AA as a proportion of total essential AA was low (11.1 to 11.2% of total essential AA for phenylalanine to 12.3 to 14.3% of total essential AA for lysine). Duodenal essential AA flow did not differ (P = 0.10 to 0.65) with forage intake level for eight of the 10 essential AA. Duodenal flow of arginine decreased linearly (P = 0.01), whereas duodenal flow of tryptophan increased linearly (P = 0.002) as forage intake increased from 30 to 105% of maintenance. Balancing intestinal essential AA supply in beef cattle can be accomplished by varying intake of a RUP supplement.
A rapid method for separation and quantitation of purines was applied to ruminal and intestinal digesta for estimating net microbial protein synthesis in the rumen. The procedure combines standard literature methods for hydrolysis of nucleotides by perchloric acid followed by precipitation of free purines with silver nitrate to separate the purines from interfering compounds. Acid resolubilized purines were quantitated spectrophotometrically at 260 nm. Microbial protein was estimated by the ratio of purines to N of isolated bacteria. The procedure is rapid, simple, precise and not costly. Duodenal passage of microbial N estimated by this procedure for steers fed semipurified and purified diets containing no protein was highly correlated (R2 = 0.98; P < 0.01) with duodenal passage of tungstic acid precipitable N. Results indicate that purines may be useful as a marker for quantitating microbial protein. Key words: Purine, RNA, DNA, microbial protein
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.
1. Three experiments were conducted to determine the flow of nitrogen through the rumen and abomasum when cows, steers and lambs were totally nourished on volatile fatty acids infused into the rumen.
2. In two dairy cows (650–700 kg) and two large steers (370–405 kg) the daily flow of non-ammonia-N (NAN) from the rumen was 50.7 and 58 mg/kg live weight (W) 0.75 respectively.
3. The flows of NAN through the rumen and abomasum in four young steers (240 315 kg) were 85.0 (SE 21.0) and 195 (SE 7.0) mg/kg W 0.75 respectively.
4. In the third experiment the effects of altering rumen pH and osmotic pressure on flow of NAN through the rumen and abomasum were investigated in lambs. While rumen pH and osmotic pressure influenced rumen volume and outflow they had no significant effect on NAN flow. The mean values for NAN outflow from the rumen and abomasum were 76 and 181 mg N/kg W 0.75 respectively.
5. Abomasal NAN flow increased with increasing abomasal pH. When osmotic pressure was greater than about 330 mosmol/l in the rumen there was a net inflow of water, while below this value there was net loss of water.
6. For all experiments the flow of N both from the rumen and abomasum was highly variable; this has to be considered if a constant value is used for endogenous N in estimating dietary N in the abomasum.
7. With N-free infusion the rumen NH a concentration varied from 50 to 120 mg NH a -N/I.
8. The amino acid composition of rumen and abomasal N was also determined. Relative to tissue Nit contained a higher proportion of cysteine.
1. A method for estimating the proportions of bacterial- and protozoal-N in the total non-ammonia-N reaching the lower gut of the ruminant under steady-state conditions was evaluated. Three trials using two different diets were conducted with a Holstein steer equipped with a rumen cannula and duodenal re-entrant cannulas.
2. An intraruminal primed infusion of ( ¹⁵ nh 4 ) 2 so 4 was administered for 68 h during each trial. Bacteria and protozoa samples were isolated from rumen fluid at approximately 6 h intervals during each infusion period. Total non-ammonia-N was isolated from duodenal digesta samples taken at approximately the same times. All of these samples were analysed for ¹⁵ N enrichment. A computer program was used to fit equations to the ¹⁵ N-enrichment curves of bacterial- and protozoal-N. Models of both bacterial- and protozoal-N kinetics consisted of a small pool which equilibrated rapidly with rumen NH 3 and a large pool with a fractional turnover rate of 0.045–0.070/h for bacterial-N and 0.056–0.069/h for protozoal-N.
3. Abomasal fluid turnover was estimated by a single injection of polyethylene glycol (molecular weight 4000) into the rumen followed by sampling of rumen fluid and duodenal digesta.
4. Estimates of abomasal fluid turnover, bacterial-N turnover, and protozoal-N turnover were entered into an equation which was adjusted by computer iteration to fit the ¹⁵ n-enrichment curve of duodenal digesta non-NH 3 -N generated from each ( ¹⁵ nh 4 ) 2 so 4 infusion period. The computer fit of this equation to the observed results gave estimates of 0.39–0.45 and 0.22–0.41 for the proportion of duodenal non-NH 3 -N derived from bacterial-N and protozoal-N respectively.
5. This method is potentially useful in estimating microbial protein passage to the lower gut in ruminants. Sampling digesta from the omasum rather than the duodenum would simplify the method and possibly increase the reliability of the estimates.
Four cows were fed once a day either a Cocksfoot hay diet (H) or a diet consisting of 65% hay and 35% pelleted ground barley (HB). 15(NH4)2SO4 was continuously infused into the rumen as a microbial marker and ruminal digesta samples were collected during the 24-h postprandial period for the isolation of liquid-associated protozoa and bacteria (LAP, LAB) and particle-associated bacteria (PAB). There were marked differences between ruminal pH diurnal variations with diets H and HB. Irrespective of the diet and sampling time, the chemical composition (OM, N, DAPA, 15N) of the protozoa was clearly different from that of the bacteria (P < .001). The LAP contained more OM but less N and 15N than the bacterial fractions. The DAPA used to validate the isolation technique for the mixed ciliate population was not detected in protozoal fractions. The OM content of LAB was lower than that of PAB, whereas the N, DAPA, and 15N contents were higher. The observed effects of diet (P < .01) on LAP mean N contents were due to the different N contents of the LAP samples isolated 23 h after feeding and were correlated with the variation in the number of Endodiniomorphid protozoa (r = .72; P < .05). The N content of LAB was not affected (P > .05) by diet but that of the PAB was increased on diet HB (P < .05). The diet did not affect the 15N content of any of the three microbial populations. However, the 15N content of the bacteria decreased shortly after feeding (P < .001).
Three lactating cows fitted with rumen cannulas and three cows fitted with proximal duodenal cannulas were used to determine the effect of in situ rumen degradation on the AA profile of rumen-undegraded protein of 12 feedstuffs. Intestinal digestibility of rumen-undegraded protein was determined using the mobile bag technique. The absorbable AA profile of rumen-undegraded protein for each feedstuff was compared with profiles of the original feedstuff and the rumen-exposed undegraded protein. Branched-chain AA in particular seemed to be rather resistant to degradation in the rumen, as was Phe. Lysine concentrations decreased in the undegraded protein fraction in 9 of 12 feedstuffs; the degradation of Met depended on the feedstuff. The absorbable AA profiles of undegraded protein, in general, closely reflected the AA profiles of the rumen-exposed residues, which suggests that rumen degradation had a greater influence than postruminal digestion on the postruminal provision of specific absorbable AA. Intestinal digestibility of undegraded protein varied from 37.8% for Eragrostis curvula hay to 98% for soybean meal; the constant digestibility factor used by most protein systems should be reconsidered.
Four ruminally cannulated cows were used to compare amino acid (AA) composition of protozoal and bacterial fractions as affected by sampling time and diet. Cows were given once a day restricted feed (80% of ad libitum intake) of 7 kg DM with two successive diets. Diet HB was 65% Cocksfoot hay and 35% pelleted ground barley, and Diet H was 100% Cocksfoot hay. Samples of whole ruminal contents were taken 2, 5, 8, 11, and 23 h after feeding for Diet HB and 2 h after feeding for Diet H to isolate the liquid-associated protozoa and bacteria (LAP, LAB) and particle-associated bacteria (PAB). At each sampling time, the AA compositions of the different microbial populations were determined. The AA profiles of the LAP were different from those of the bacteria for 13 AA out of 17 studied. Differences between AA compositions of LAB and PAB were also observed for 10 AA out of 17 studied. Irrespective of the microbial population, AA composition did not vary with sampling time after feeding diet HB (P > .05; except for arginine, glutamate, and glycine). The AA contents of none of the three microbial populations were affected (P > .05) by the diet except for leucine and glutamate (P < .01). The differences in AA profiles between LAP and bacteria and between LAB and PAB confirm the importance of the representativeness of the microbial reference sample for correctly estimating microbial AA flow into the small intestine.
Whole animal mathematical models have become widely accepted as the only practical way to incorporate the vast amount of published data into conceptual models of animal metabolism. The ability to accurately predict dietary N requirements of dairy cows depends upon the ability to accurately measure digesta flow and identify the origins of its N. Four lactating Holstein cows were fed a low-protein (9.8% CP of DM) ration of 28.6% timothy silage, 27.2% whole crop barley silage, and 44.2% grain-based concentrate (DM basis). This was supplemented with 1.3 kg d-1 of ground barley mixed with either no protein supplement, 1.11 kg of soybean meal, 0.67 kg of blood meal or 0.20 kg of urea. Rumen bacteria and protozoa were isolated and assayed for components. Rumen ingesta were manually evacuated to estimate rumen pool sizes, and duodenal digesta were sampled to estimate intestinal flow. Use of diaminopimelic acid (DAPA) was judged to result in rumen bacterial N pool sizes that were quantitatively reasonable and reflective of expected changes due to treatments. Conversely, use of ribonucleic acid (RNA) was judged to underestimate the rumen microbial N pool size and result in biologically implausible differences due to treatments. Use of DAPA was judged to slightly underestimate duodenal flow of bacterial N and suggested changes due to treatments consistent with expectations. In contrast, RNA suggested biologically implausible differences in duodenal flow of bacterial N due to treatments. A novel mathematical procedure utilizing both DAPA and RNA to estimate rumen pool sizes and intestinal flows of bacterial and protozoal N did not provide biologically plausible estimates thereby demonstrating that at least some of the assumptions relative to use of DAPA and RNA are not correct.
A method is proposed for estimating the percentage of dietary protein that is degraded by microbial action in the rumen when protein supplement is added to a specified ration. The potential degradability, p , is measured by incubating the supplement in artificial-fibre bags in the rumen and is related to incubation time, t , by the equation p = a+b (1 – e -ct ). The rate constant k , measuring the passage of the supplement from the rumen to the abomasum, is obtained in a separate experiment in which the supplement is combined with a chromium marker which renders it completely indigestible. The effective percentage degradation, p , of the supplement, allowing for rate of passage, is shown to be p = a +[ bc/(c+k) ] (1- e -(e+k)t ) by time, t , after feeding. As t increases, this tends to the asymptotic value a+bc /( c+k ), which therefore provides an estimate of the degradability of the protein supplement under the specified feeding conditions.
The method is illustrated by results obtained with soya-bean meal fed as a supplement to a dried-grass diet for sheep. The incubation measurements showed that 89% of the soya-bean protein disappeared within 24 h and indicated that it was all ultimately degradable with this diet.
When the dried grass was given at a restricted level of feeding the allowance for time of retention in the rumen reduced the estimate of final degradability to 71% (69% within 24 h). With ad libitum feeding there was a faster rate of passage and the final degradability was estimated to be 66% (65% within 24 h).
Two crossbred wethers ( c . 45 kg) and two Hereford heifers ( c . 215 kg) were fitted with permanent cannulas in the rumen and abomasum and given a diet of lucerne hay and barley (60:40). Organic matter (OM) intakes were 0·67 kg/day for sheep and 3·14 kg/day for cattle.
The mean numbers of protozoa in the rumen fluid were 9·3 × 10 ⁵ /ml for sheep and 7·4 × 10 ⁵ /ml for cattle. ¹⁴ C-labelled protozoa were prepared by incubating rumen fluid in vitro with [ ¹⁴ C]methyl choline and then isolating them by sedimentation and differential centrifugation. The labelled protozoa were returned to the rumen of each of the donor animals in a single injection. The specific radioactivity in mixed protozoa isolated from the rumen was measured for 3 days. The protozoal pool size was 10 and 12 g N in the sheep and 64 and 44 g N in the cattle. Protozoal N contributed, on average, 48% of the total N in the rumen.
Production of protozoal N in the rumen was 9·5 and 11·2 g/day for the sheep and 49·5 and 38·6 g/day for the cattle. The flow of protozoal N from the abomasum was calculated to be 1·6 and 2·9 g/day for sheep and 17·3 and 13·3 g/day for cattle. Thus, on average, 79% of the protozoal N was recycled within the rumen of the sheep and 65% within the rumen of the cattle. Protozoal N made up 11–20% of total N flow from the abomasum. The turnover times of ¹⁴ C-labelled protozoa injected into the rumen of the sheep and the cattle were similar (26·2 and 26·8 h for sheep; 30·8 and 27·5 h for cattle) and were similar to those for protozoa isolated from the rumen of sheep after direct intraruminal injection of [ ¹⁴ C]methyl choline (28 and 36 h).
In situ evaluation of the duodenal amino acid (AA) profile was attempted in a 4 × 4 Latin square study using four lactating Holstein cows fitted with ruminal and duodenal cannulas. Dietary supplemental crude protein (CP) sources, making up 40% of the dietary CP, were: soybean meal, cottonseed meal, corn gluten meal or urea. Duodenal flow of organic matter (OM) and CP was determined in vivo by means of constant infusion of ytterbium and chromium, and predicted in situ from rumen degradation. Purines were used as microbial markers. In situ calculation of the AA profile, expressed as g AA in 100 g of total AAs, was based on the composition of AA in feed and in isolated bacteria as well as on in situ rumen degradation of OM and CP. The AA profile in the duodenum when assessed in vivo was affected by the nature of the supplemental protein; in situ assessment of the AA profile resulted in comparable profiles. The data are interpreted to suggest that the in situ method enables prediction of the profile of AA (g AA/100 g total AA) flowing to the duodenum, and that the undegraded portion of supplemented protein affects that profile.
The amino acid (AA) profile of dietary absorbable proteins may not always be the best for optimal milk protein synthesis, as demonstrated by experimental post-ruminal supplementation of methionine and lysine. Nevertheless, the AA profile of absorbable protein can vary widely with the diet. To be able to balance most of diets according to the main limiting AA, it is crucial to predict the AA composition of duodenal digesta. This article describes an attempt to predict the duodenal AA composition, based on the PDI system and literature reports of the AA composition of rumen microbes, rumen undegraded feed proteins and endogenous proteins. Results from this initial model were tested against AA compositions measured in 133 cattle diets. With most AA the tests revealed slight biases (less than 5% differences) in the mean value predictions except for Met and Gly (12 and 14% differences). Moreover, the model tended to underestimate (−0.1 to −18.3%) low AA contents and overestimate (+0.3 to 14.5%) high ones. The initial model was adjusted for these biases by covariance analysis. After correction the data were predicted with a good degree of confidence for Lys Arg, Thr, Val, Leu, Asp, Ser, Glu and Pro (0.65<R2<0.80). The residual variations were generally low (<6%) except for His, Met, Pro and Gly (7 to 14%). Factors susceptible of inducing bias, such as the estimated proportion and composition of microbial protein AA or AA composition and content in undegraded dietary protein, are discussed.
The intestinal disappearance and simultaneous arterial inflow and portal appearance of individual amino acids (AA) were studied in sheep fed closed formula, unrefined high (H.P.) and medium (M.P.) protein diets. Gut contents were sampled through four intestinal cannulae and blood was sampled through portal and arterial catheters. The amount of total and amino N that was fed decreased on passage into the duodenum but increased in the jejunum, and then again decreased steadily towards the terminal ileum. The amounts of AA passing into the duodenum were significantly higher when the H.P. rather than the M.P. diet was fed. No dietary differences in AA were noted at the ileo-cecal junction, however, meaning that greater amounts of AA disappeared from the intestine when the H.P. diet was fed. The amounts of AA appearing in portal blood were 30 to 80% of those disappearing from the intestine and were greater in sheep fed the H.P. diet. The amount of AA passing into the duodenum also significantly affected the concentrations of AA in arterial blood. Less [U-14C]glutamic acid than [U-14C]alanine, that was infused into abomasum, was detected in the digesta passing through the pylorus. The same also was true for the unlabeled free form of glutamic acid. The portal appearance of both unlabeled and labeled glutamic acid was negligible, but that of alanine was considerable. Variable amounts of [14C]citrulline, [14C]arginine, and [14C]urea were detected in the blood following the abomasal infusions of labeled glutamic acid or alanine. The portal appearance of these labeled metabolites was always negative, however, implying that they were utilized, and not formed, by gut tissues.
Microbial fractions, comprising protozoa, large and small bacteria and whole particulate matter, have been isolated from rumen contents of sheep given a mainly concentrate diet, a mixture of hay and concentrate, and hay only. Samples of rumen contents were taken before and 2 h after feeding. The main components determined were: protein, lipid, nucleic acids, carbohydrate and ash. The amount of cell wall was estimated in terms of known cell wall constituents (diaminopimelic acid (DAP) and glucosamine). The concentration of some of the constituents varied with diet and with respect to the time of feeding. Many of the differences disappeared when the results were expressed on a polysaccharide-free basis. The amino acid composition of large and small bacteria was virtually the same. The amino acid composition of protozoa was similar except for the proportions of glutamic acid and lysine which were greater in protozoa, and alanine, glycine and DAP, the proportions of which were greater in bacteria. There were higher proportions of protein in large bacteria and protozoa than in small bacteria. Small bacteria contained more lipid, ash and DNA, and less RNA than the other two fractions. The polysaccharide content of protozoa and large bacteria increased from about 8% before feeding to about 30% after feeding, while the polysaccharide content of small bacteria increased only slightly after feeding.
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.
Four multiple-cannulated steers (340 kg) were used in a 4 X 4 Latin square design with a 2 X 2 factorial arrangement of treatments. Steers were fed a diet of 50% ground hay and 50% concentrate at two intakes (1.4 and 2.1% of BW), with urea and 15N-enriched ammonium sulfate infused continuously into the rumen at .4 or 1.2% of diet DM. Ratios of purines and diaminopimelic acid-N to N in fluid-associated and particulate-associated bacteria and in protozoa were similar among treatments but were lower for protozoa than for bacteria. Diaminopimelic acid-N:N was higher for fluid-associated vs. particulate-associated bacteria. Enrichment of 15N was similar between bacteria among treatments and was 30% lower for protozoa. Turnover rates of 15N in bacteria, NH3N, and non-NH3N pools were faster for steers infused with 1.2 than those infused with .4% urea, indicating less efficient usage of ammonia with higher urea. A method is described to estimate the proportion of duodenal nitrogen comprising bacterial and protozoal nitrogen.
A new liquid marker, cobalt-ethylenediamine tetraacetic acid (EDTA), and two solid markers, chromium (Cr) and cerium (Ce) mordanted plant cell walls, were investigated. Synthesis and methods of analysis are described for the markers. The Cr- and Ce-cell wall complexes were tested for stability to EDTA, hydrochloric acid and rumen microorganisms. Plant cell walls were rendered indigestible by mordanting with Cr and 98% of the marker remained on the fibre after a simulated sequence (in vitro) of digestion. Ce-mordanted cell walls were 35% digestible in vitro using a rumen culture, and 56% of the marker could be washed off the remaining fibre. Treatment with EDTA removed all Ce and 15% of the Cr. Hydrochloric acid (0.01M) had a negligible effect on the removal of Cr from the cell walls, whereas 0.1M acid removed, on average, 10% of the marker. Losses of Cr from the mordant may be related to the quality of the preparation. Co-EDTA was found to be comparable to Cr-EDTA. The urinary excretion of Cr and Co was 2–3% in most animals except in rabbits, which excreted as much as 30% of the liquid markers in the urine.
Four Holstein cows were used in a 4 x 4 Latin square design to investigate the effects of soybean hulls and lignosulfonate-treated soybean meal on ruminal fermentation and nutrient passage to the duodenum. Diets contained 32% corn silage, 19.8% alfalfa-grass hay, and 48.2% concentrate (DM basis). Treatments, arranged in a 2 x 2 factorial, were concentrate mixes based on 1) corn and soybean meal, 2) corn and treated soybean meal, 3) soybean hulls and soybean meal, and 4) soybean hulls and treated soybean meal. Individual protein supplements supplied 40% of dietary CP, and corn or soybean hulls constituted 28% of dietary DM. Intake of OM (mean 18.9 kg/d) was similar among treatments, but intake of NDF was 42% greater, and intake of nonstructural carbohydrate was 55% less, for cows fed soybean hulls. Passage of OM to the duodenum was similar among diets, but flow of NDF was 43% greater, and flow of nonstructural carbohydrate was 56% less, for cows fed soybean hulls. Ruminal pH was similar, but total concentrations of VFA increased 7% when soybean hulls replaced corn. Ruminal digestion of dietary CP was 15% less for cows fed treated soybean meal, but bacterial N flows were similar among treatments. Soybean hulls were digested to a similar extent as corn, but few interactions occurred between supplemental carbohydrate and protein sources.
Results obtained during the past decade indicate clearly that protozoa are actively involved in the degradation of dietary and microbial proteins in the rumen. Because of the great ability of protozoa to ingest the particulate matter suspended in the rumen, protozoa are more active in degrading insoluble than soluble proteins. This indicates that studies carried out using lysed and sonicated protozoa are not appropriate for quantifying the actual contribution of protozoa to protein degradation in the rumen. In vivo trials have confirmed that duodenal flow of both undegraded dietary protein plus bacterial protein generally is increased by defaunation. The decrease in ruminal ammonia concentration consistently observed after defaunation accounts for the lower urinary nitrogen (N) excretion found in defaunated animals, whereas the increase in fecal N excretion in the same animals probably results from a shift of plant cell wall digestion from the rumen to the large intestine. Total N excretion is not altered significantly by defaunation. A summary of literature data indicates there are contradictory effects of defaunation on ruminant performance. This implies that animal response to defaunation may depend on the specific nutrient-limiting performance on the one hand and on the modifications of digestion and metabolism resulting from defaunation on the other. Different methods are proposed to either eliminate or decrease the numbers of ruminal protozoa or to alter their makeup. However, none of these approaches has been tested under practical feeding conditions.
The amino (AA) profile of eight feedstuffs (two samples of fishmeal, soybean meal [SBM], formaldehyde-treated SBM, sopralin, cotton-seed meal [CSM], rapeseed meal [RSM], corn distillers grains [CDG], and corn gluten feed [CGF]) was determined before and after ruminal incubation for 8 and 12 h in three lactating Friesian cows using nylon bags. The profile of AA disappearing during intestinal passage was also measured by inserting the bags into the duodenum through T-piece cannulas after ruminal incubation and recovering them in the feces. The AA profile changed for all feedstuffs, except sopralin, following ruminal incubation. Changes were greater for the more degradable feedstuffs. The profile of AA disappearing during intestinal passage was generally similar to the profile after ruminal incubation, but some differences were found with feedstuffs that had low (< 84%) intestinal disappearance of AA (RSM, CDG, CGF). For the other feedstuffs, intestinal disappearance of AA was greater than 93%. The two fishmeal samples had the highest concentrations of methionine and lysine in their residues after ruminal incubation, whereas CDG and CGF had low lysine concentrations. Residues of these latter two and RSM were quite high in methionine concentration, whereas residues of SBM, sopralin, and CSM had the lowest concentrations. Corn distillers grains had 13% of its AA remaining after ruminal incubation followed by intestinal passage. These results show that feedstuffs vary in the proportion of their AA that escape ruminal degradation, in the profile of those AA, and in their intestinal digestibility. These factors should be considered in protein evaluation systems and in assessment of the protein quality of feedstuffs.
Four Holstein cows in midlactation were equipped with ruminal and abomasal cannulas and used to study the effect of synchronized degradation of crude protein (CP) and organic matter (OM) and feeding frequency on digestion and outflow of nutrients. A 4 x 4 Latin square design was used. Diets were arranged in a 2 x 2 factorial design; the four diets contained high ruminally degradable OM and high ruminally degradable CP, high ruminally degradable OM and low ruminally degradable CP, low ruminally degradable OM and high ruminally degradable CP, and low ruminally degradable OM and low ruminally degradable CP. In each period, cows were fed four times daily from d 1 to 14 and two times daily from d 15 to 28. Mean daily ruminal ammonia N concentration was reduced by high ruminally degradable OM, low ruminally degradable CP, and twice daily feeding. Fluctuation in ruminal ammonia N was lower when cows were fed four times daily than when cows were fed twice daily. Plasma urea N concentrations were lower for cows fed diets that were high in ruminally degradable CP. Higher CP flow in the abomasum was found for cows fed the diet containing high ruminally degradable OM and low ruminally degradable CP. Microbial dry matter and CP flow to the abomasum were higher for cows fed twice daily than for cows fed four times daily. Flow of OM in the abomasum was not altered by concentrations of ruminally degradable OM or CP. These results suggest that the available energy in the rumen (ruminally degradable OM) is the most limiting factor for ruminal N utilization under our experimental conditions. Use of these data may improve the prediction of plasma urea N.