| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Animal and Veterinary Science, University of Idaho, Moscow, ID 83844-2330
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Key Words: dairy cow • carbohydrate • rumen ammonia • milk protein
Abbreviation key: AIA = acid-insoluble ash, ANDF = available NDF, APE = atom percent excess, AUC = area under the curve, MN = microbial nitrogen, MUN = milk urea nitrogen, NSC = nonstructural carbohydrates, NSP = nonstarch polysaccharides, PDA = polysaccharide-degrading enzyme activities, RFNDF = ruminally fermentable fiber, RFSS = ruminally fermentable nonstructural carbohydrates, RS = reducing sugars, TFC = total fermentable carbohydrates
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
The objective of this work was to investigate the effects of different dietary ratios of ruminally fermentable nonstructural carbohydrates to fiber on ruminal fermentation, nutrient digestibility, urinary N losses, milk yield and composition, and transfer of ruminal ammonia N into milk protein in dairy cows.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
) contained similar proportions of alfalfa forage but had either a higher concentration of ruminally fermentable nonstructural carbohydrates (NSC, as starch and sugars; Diet RFSS) or ruminally fermentable fiber (RFNDF) provided with the nonforage components. Dietary concentrations of carbohydrate fractions were analyzed and concentrations of protein fractions and energy content of the diets were estimated using the CPM Dairy program (version 2.0.23, University of Pennsylvania, Kennett Square, PA, Cornell University, Ithaca, NY and William H. Miner Agricultural Research Institute, Chazy, NY). Since studying ruminal ammonia utilization and transfer was the focus of this trial, diets were formulated to have high CP content and provide high ammonia concentrations in the rumen. The diets were fed as total mixed rations three times a day at 0600, 1400, and 2200 h. Cows were fed at 90% of ad libitum intake determined before initiation of each experimental period. Diets were mixed in a Data Ranger (American Calan Inc., Northwood, NH). Refusals were collected and weighed daily; composited samples (per cow and per period) were analyzed for chemical composition. Each experimental period consisted of 14 d adaptation to the diet and 7 d of sampling.
|
Total tract apparent digestibility of nutrients was determined using acid-insoluble ash (AIA; Van Keulen and Young, 1977) as an internal digestibility marker. Concentration of AIA in dietary DM was (mean ± SE) 1.34 ± 0.104 and 1.60 ± 0.130%, RFSS and RFNDF, respectively. Nutrient digestibility was calculated as described by Schneider and Flatt (1975). Flow of DM and nutrients at the duodenum was determined using the double-marker method of Faichney (1975). Li/Co-EDTA and AIA were utilized as liquid and solid phase markers, respectively. Li/Co-EDTA (Uden et al., 1980) was applied to the diets at a daily dose equivalent to 4.2 g of Co/cow from d 5 through the last day of each period. Microbial protein flow to the duodenum was determined with purines as a microbial marker, assuming all purines present in duodenal digesta were of microbial origin. True digestibility of DM, OM, and NAN in the rumen was calculated as: total duodenal flow of DM, OM, or NAN - duodenal flow of microbial DM, OM, or NAN. Cr-EDTA (Uden et al., 1980) was used as a ruminal liquid passage rate marker and was pulse-dosed (equivalent of 2.5 g Cr) into the rumen of the cows at 0600 h on d 15 of each period.
Samples and Analyses
Feeds.
Diets and individual feed samples were dried at 70°C to constant weight in an air-forced oven and analyzed for ash, total N, and CP insoluble in NDF solution (Hristov et al., 2001), NDF and ADF (Ankom 200 Fiber Analyzer, Ankom Technology), lignin (sulfuric acid lignin, DaisyII Incubator, Ankom Technology), starch (McCleary et al., 1994; total starch analysis kit from Megazyme International Ireland Ltd., Wicklow, Ireland), and ether extract (AOAC official method 920.39, AOAC International, 1999). A heat-stable amylase (
-amylase, EC No 232-560-9, Sigma Chemical Co., St. Louis, MO) was used in the NDF analysis; sodium sulfite was not used in the analysis. Molasses composition was obtained from the manufacturer (Westway Trading Corp., Minneapolis, MN). Concentration of NSC in individual feed ingredients and the diets was calculated as: NSC = 100 - [CP + (NDF - NDFCP) + ash + ether extract] (CPM Dairy). Concentration of nonstarch polysaccharides (NSP) was calculated as: NSP = NSC - starch (Van Soest et al., 1991). Available NDF (ANDF) was calculated as: ANDF = NDF - (lignin x 2.4) (CPM Dairy). Intake of ruminally fermentable ANDF, starch, and NSP was calculated as: DMI from a dietary ingredient x concentration of ANDF, starch, or NSP in the dietary ingredient x [kd/(kd + kp)], where kd and kp were rate of degradation and rate of passage, respectively. Rate of degradation (kd) was taken from CPM Dairy and kp was calculated based on DMI, BW, and forage content of the diet (for forage ingredients) and forage kp (for concentrate ingredients) (CPM Dairy). Rates of degradation of carbohydrate fraction B2 (cellulose and hemicellulose) were applied to ANDF and of fraction B1 (starch, pectins, and ß-glucans) - to starch and NSP. Carbohydrate fraction A rates were used for molasses NSP; for simplicity, the difference in degradation rates between soluble sugars and other NSP components of the other dietary ingredients was considered to have a minor effect on NSP rate of fermentation. This type of approach assumes homogeneity of the starch or NSP fractions among individual feeds. For example, while in corn grain (RFNDF) fraction B1 will be predominantly starch, fraction B1 of barley grain or beet pulp will contain large quantities of soluble fiber (ß-glucans or pectins, respectively; Van Soest et al., 1991). Total dietary intake of ANDF, starch, or NSP was the sum of the intakes with the individual ingredients. Total fermentable carbohydrates (TFC) intake was calculated as: TFC intake = fermentable ANDF intake + fermentable starch intake + fermentable NSP intake.
Rumen.
Rumen samples were taken before (0 h, background) and 1, 3, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 53, 57, 61, 65, 69, 72, 75, 78, 84, 90, 96, 102, 108, and 114 h after initiation of the (15NH4)2SO4 infusion. Samples were taken from four locations in the rumen: ventral sac, reticulum, and two from the feed mat in the dorsal rumen (approximately 250 g each). The four samples were composited and squeezed through two layers of cheesecloth. The filtrate was stored on ice and analyzed for pH, ammonia, VFA, reducing sugars (RS), and polysaccharide-degrading (PDA; carboxymethylcellulase, amylase, and xylanase) and deaminative enzyme activities as described elsewhere (Hristov et al., 2000a). Proteolytic activity in ruminal fluid was determined using 15N-labeled casein as a substrate according to Hristov et al. (2002). Ammonia samples were also analyzed for 15N enrichment (Hristov et al., 2001). Bacterial pellets were isolated through differential centrifugation (an initial centrifugation at 400 x g for 5 min and a subsequent centrifugation of the low-speed supernatant at 20,000 x g for 15 min at 4°C), freeze-dried, and analyzed for OM, N and 15N enrichment (Hristov et al., 2001) and purines (Makkar and Becker, 1999). Samples taken at 0, 1, 3, 5, 9, 13, and 17 h were analyzed for Cr concentration (Iris ICP atomic emission spectrophotometer, Thermo Jarrell Ash Corp., Franklin, MA).
Duodenum.
Duodenal samples (300 ml per sampling) were taken at 0900, 1500, and 2100 h (d 4), and at 0300, 0600, 1200, 1800, and 0000 h [d 5 and 6 of the (15NH4)2SO4 infusion]. Samples were stored frozen at -40°C. After thawing, digesta samples were composited on a weight basis (per cow and period). The composited samples were separated into fluid and solid phases by filtering through a 100 µm fabric (Sefar America Inc., Depew, NY). Both phases were freeze-dried, ground through 1 mm sieve, and analyzed for OM, Co (Iris ICP atomic emission spectrophotometer), AIA, N and NAN (Firkins et al., 1992), purines, NDF, and ADF.
Feces and Urine.
Grab fecal samples (200 g per sampling) were collected from the rectum at the same sampling times used for duodenal digesta. Samples were composited per cow and period and oven-dried at 70°C to constant weight. Samples were ground through 1 mm sieve and analyzed for OM, N, C (model 1500 C/N analyzer, Carlo Erba Instruments, Milan, Italy), AIA, NDF, and ADF. Urine was collected during the last three days of each period. Catheters and sample preparation are described elsewhere (Hristov et al., 2000b). Urine samples were analyzed for N and allantoin (Hristov et al., 2000b).
Milk.
Total milk output was measured and milk was analyzed for fat, protein, and milk urea nitrogen (MUN) (Treasure Valley Milk Testing Lab, Nampa, ID) during the last 7 d of each period. After initiation of the (15NH4)2SO4 infusion, cows were milked at: 0 (background), 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 125, 135, 145, and 155 h. At each milking, milk weights were recorded and two milk samples were taken: one for analyses of milk fat, protein, and MUN and another for analysis of 15N-enrichment of milk protein. Milk protein was precipitated with 65% (w/v) solution of TCA at 5% (w/v) final concentration. Protein pellets were sedimented by centrifuging at 20,000 x g for 15 min at 4°C, freeze-dried, and analyzed for N and 15N-enrichment.
Calculations and Statistical Analyses
Milk and ruminal bacteria 15N-enrichment (APE) curves were plotted vs time and fitted to the multicompartmental model of Dhanoa et al. (1985), restricted to two compartments and to a five-parameter modified Gaussian model (SigmaPlot 5.0, SPSS Inc., Chicago, IL), respectively. Criteria for best fit were: R2 (the coefficient of determination), the ANOVA P value for the regression (describing the association between the dependent and independent variables), the Predicted Residual Error Sum of Squares (PRESS, an indicator of how well a regression model predicts new data), the Normality test (indicating the normality of distribution of source population around the regression), and the residuals distribution around the 0 line. Ammonia concentration in the rumen of the cows varied greatly during sampling and 15N infusion (Figure 1). As a result, regression models were not created for 15N enrichment of ruminal ammonia N and consequently, proportions of bacterial and milk protein N originating from ammonia N were not calculated. Areas under the predicted milk protein and bacterial 15N curves (AUC; 15N atom % excess in milk protein N or bacterial N x h) were computed using the trapezoidal rule (AREA.XFM transform, SigmaPlot 5.0). Proportions of milk protein N originating from ruminal bacterial N were derived based on the respective AUC (Nolan and Leng, 1974).
|
 | (1) |
where µ is the overall mean, G, C, P, and D are group, cow, period, and diet, and e is an error term under the usual assumptions for ANOVA.
Rumen fermentation data were averaged per period and cow.
The cumulative amounts of 15N excreted in milk protein (as percentage of the 15N infused in the rumen of each individual cow) were fitted to a logistic model:
 | (2) |
where: y, cumulative 15N excreted in milk protein as percentage of the 15N infused in the rumen at time x; m, theoretical maximum for y; k, rate related parameter; L, time to reach 50% of m (maximum 15N recovery in milk protein).
This model was fitted to each treatment and each model was assessed for adequate fit. The estimated models were compared using the dummy variable regression technique (Bates and Watts, 1988).
All data were analyzed using SAS (SAS, 1996).
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
). Diet RFSS had 23% lower NDF content and 51% higher starch content than diet RFNDF. Concentration of ANDF was by 33% higher and NSC was 16% lower in RFNDF than in RFSS. The diets contained similar proportions of NSP. The estimated intake of ruminally fermentable ANDF was 37% higher (P < 0.05) and that of ruminally fermentable starch was 48% lower (P < 0.001) on RFNDF compared to RFSS (Table 2). Thus, the intake of ruminally fermentable fiber was significantly higher in the cows fed RFNDF whereas the intake of ruminally fermentable starch was higher in the cows fed the RFSS diet. Cows fed RFSS had higher (33%; P < 0.05) intakes of NSC and tended to have higher (P < 0.1) total fermentable CHO intake than the cows fed RFNDF.
|
). Ammonia concentration was lowered (P < 0.05) by RFNDF compared to RFSS. Polysaccharide-degrading and deaminative or proteolytic activities in the rumen were not affected (P > 0.05) by treatment. There were no differences (P > 0.05) in total or individual VFA concentrations or acetate to propionate ratio between the diets. Fractional outflow rate of the fluid phase of the rumen contents did not differ (P > 0.05) between diets. Microbial nitrogen (MN) flow to the small intestine was similar (P > 0.05) between the diets. Similarly, daily excretion of urinary allantoin or the efficiency of microbial N synthesis in the rumen were not different (P > 0.05) between the diets.
|
); except apparent CP digestibility in the reticulo-rumen was higher (P < 0.05) for RFSS compared to RFNDF. True ruminal DM digestibility tended to be higher (P < 0.1) on RFSS than on RFNDF. Fecal ammonia-N concentration was similar (P > 0.05) between the two diets and fecal C:N ratio tended to be higher (P < 0.1) for RFSS than for RFNDF.
|
). Average MUN content of milk was lower (P < 0.05) for RFNDF than for RFSS.
|
). There were no differences (P > 0.05) in N excreted with urine or feces between the two diets. From 35 (RFNDF) to 37% (RFSS) of the ingested N was excreted with the urine and from 23 (RFSS) to 32% (RFNDF) with the feces. Numerically, larger proportion of the total N lost to the cows was excreted with the urine when RFSS was fed and with the feces when RFNDF was fed.
|
). Bacterial N from RFSS cows had higher (P < 0.01) 15N-enrichment than bacterial N from RFNDF cows. The area under the ruminal bacterial 15N curve was larger (P < 0.01) for RFSS than for RFNDF. The area under the milk protein 15N curve was larger (P < 0.05) for RFNDF than for RFSS. The estimated proportion of milk protein N originating from ruminal bacterial N was 50% higher (P < 0.01) when cows received the RFNDF diet vs the RFSS diet. Between 12.7 (RFSS) and 14.4% (RFNDF) of 15N infused intraruminally was recovered in milk protein N after 155 h of milking. The proportion was higher (P < 0.01) for RFNDF than for RFSS. Time to reach 50% of maximum 15N recovery and rate of 15N excretion in milk protein were not different (P > 0.05) between the two diets. The overall excretion lines (Figure 2) were different at P < 0.05.
|
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Thus, the main dietary factors that could have affected the results from the present trial were: the higher starch content and higher starch degradation rate of barley vs. corn and presence of free sugars from molasses in RFSS and the provision of greater amount of ruminally fermentable fiber with RFNDF. Comparing diets with different rates of starch degradability in the rumen (barley vs. corn), Casper et al. (1990) found increased propionate production and decreased ammonia concentration with the barley diet, although in a latter study, the effects were related to the level of ruminally degradable protein (Casper et al., 1999). Similarly, a trend for increased propionate with diet RFSS was observed in the present experiment. Leiva et al. (2000) indicated no difference in ruminal VFA and lactate concentrations, N balance or recovery, and milk yield between diets containing soluble fiber (citrus pulp) and starch (corn). In the present study, ruminal ammonia concentration was lower with the RFNDF diet. The lower (-13%) intake of total dietary N, respectively ruminally degradable N, in RFNDF compared to RFSS was most likely the main reason for the reduced concentration of ruminal ammonia with the former diet. Structural carbohydrate-fermenting ruminal bacteria derive their N exclusively from ammonia (Russell et al., 1992); it is possible that enhanced growth of fiber-degrading populations with RFNDF contributed to the reduction in ammonia concentration with this diet. Addition of readily available carbohydrates to the diet can produce variable effects on ruminal fermentation; sugar and starch supplementation of a forage diet increased dietary OM and NDF digestibility but had a negative effect on ruminal fermentation as total VFA concentration was reduced and ammonia concentration was increased (Heldt et al., 1999b). In another study, addition of 5% sugars to a fresh ryegrass/corn grain-based diet did not result in any significant effects on ruminal fermentation or milk yield and composition (McCormick et al., 2001). In this latter experiment, blood plasma urea levels were increased with the sugar addition. Diets, in which brewer’s grains replaced part of the forage, produced higher propionate concentrations in the rumen but had no effect on total VFA concentration; when brewer’s grains replaced dietary concentrate, ruminal ammonia levels were reduced compared to the control diet (Younker et al., 1998). Pereira and Armentano (2000), however, found no effect of the addition of nonforage NDF from wheat middlings and brewer’s grains on ruminal VFA and ammonia concentrations. Rumen function and chewing activity were not affected when forage NDF in the diet was replaced with nonforage fiber sources (Slater et al., 2000).
Both CPM Dairy and NRC 2001 (NRC, 2001) models predicted higher microbial protein flow at the duodenum with RFSS than with RFNDF (2233 vs 1985 and 2009 vs. 1781 g/d, CPM Dairy and NRC 2001, RFSS and RFNDF, respectively) reflecting carbohydrate composition (CPM Dairy) or total TDN content of the diets (NRC, 2001). Only a numerical difference in the microbial protein flow between the two diets was found in the present experiment. Most published work indicates microbial protein synthesis in the rumen is energy-dependent rather than nitrogen-dependent. Microbial protein produced in the rumen was found to always be higher when the diet contained higher proportion of nonstructural carbohydrates in DM (Hoover and Stokes, 1991). Despite some reports where increased dietary starch degradability had no effect on microbial protein synthesis (Shabi et al., 1998), diets containing larger amounts of ruminally fermentable starch, usually produce higher microbial protein yields. Hall and Herejk (2001) fed bermudagrass NDF alone or in combination with sucrose, pectin or starch to mixed ruminal populations in vitro. The authors reported that pectin and sugar-supplemented diets produced lower maximal TCA-precipitable protein (assumed to be microbial protein) than the starch diet.
Both, brewer’s grain and sugar beet pulp contain higher levels of ruminally fermentable NDF per kg of DM than barley (149 and 109%, respectively; Tamminga et al., 1990) and total tract NDF digestibility is also high compared to common forages such as alfalfa silage (Sievert and Shaver, 1993). Inclusion of brewer’s grain and sugar beet pulp in the present study, however, only numerically increased ruminal and total tract digestibility of fiber fractions, particularly ADF digestibility. Similarly, Younker et al. (1998) did not find any significant effects of brewer’s grains on site of NDF digestion, ruminal or total tract NDF digestibility, bacterial N flow to the small intestine, or milk yield and composition. In a trial with growing steers, the effect of supplemental carbohydrates on OM and NDF digestibility was largely dependent on ruminally available N in the diet (Heldt et al., 1999a). Although starch, glucose, or fiber (oat) supplementation generally increased digestion, reduced ammonia, and increased ruminal concentration of VFA, a number of two- and three-way interactions rendered the results difficult to interpret. Pereira and Armentano (2000) investigated the effects of two levels of forage NDF and addition of nonforage NDF (wheat middlings and brewer’s grains) on rumen fermentation and nutrient digestion. The experimental design resulted in three dietary levels of starch and free glucose. The nonforage fiber diet had lowered digestibility of DM and OM but NDF digestion was not affected. The authors concluded that addition of ruminally degradable fiber did not affect total tract NDF digestion (Pereira and Armentano, 2000).
Transfer of ammonia N into milk protein was measured directly; total excretion of ammonia N tracer in milk protein was determined gravimetrically. Expressed as proportion of 15N infused into the rumen, more 15N was recovered in milk protein with RFNDF than with RFSS. In agreement, the 15N-AUC in milk protein was larger for RFNDF than for RFSS. The specific 15N-enrichment of bacterial N and the area under the 15N-bacterial N curve were larger with RFSS than with RFNDF indicating a more intensive incorporation of 15N tracer by RFSS bacteria but also a potentially smaller overall bacterial N pool with this diet compared to RFNDF. These two effects were not separated in this trial. Since total milk protein yield was not different between the diets (in fact, it was numerically higher for RFNDF), the larger amount of 15N recovered in milk protein from RFNDF cows could be most likely explained with a larger total flow of bacterial N to the small intestine, which in turn was used for milk protein synthesis by the cows. This hypothesis, however, was not supported by the similar microbial protein flows or urinary allantoin excretion between the two diets. Methodological problems with the procedures used in this experiment may have prevented detection of existing differences in microbial N flow from the rumen between the diets. Reports have indicated a considerable recovery of feed purines in duodenal digesta; from 23% of the total purine bases in digesta (Perez et al., 1997) to 17 to 26% in duodenal solids purine bases (Hristov et al., 2000c). It is possible that, due to fractionation of bacterial/microbial purines between the reticulo-rumen and the duodenum, MN flow to the small intestine was not accurately estimated in the present trial. Studies with another widely used bacterial marker, diaminopimelic acid (DAPA), indicated a significant dissociation of cell-contained DAPA before reaching the point of sampling—the duodenum (Denholm and Ling, 1989). Due to disproportional metabolism, the ratio of microbial purine bases to NAN in digesta phases could be significantly different than the ratio in ruminal bacterial cells. As a result, a significant discrepancy between the amount of NAN from microbial origin (carrying the 15N label) and the amount of microbial purines reaching the duodenum may occur. Due to liberation of free intracellular NAN, this phenomenon is more likely to be observed in the fluid phase of digesta. In such a situation, there will be a significant discrepancy between the measurements of bacterial/microbial flow to the duodenum using 15N vs purines as microbial markers. The data of Perez et al. (1997) showed that the microbial contribution to the duodenal NAN, estimated using purine bases as microbial marker, was 97, 74, 88, and 83% (liquid-associated bacteria composition; four diets) of the microbial contribution derived using 15N as a marker. Estimates based on our previous data (Hristov et al., 2000c), indicated that purine-estimated microbial contribution to NAN in fluid duodenal digesta was 0.36 and 0.55 (barley and corn-based diets, respectively) of the 15N-derived estimates. In the solid phase of digesta, however, the two methods gave similar estimates: ratios of 0.89 and 1.02, respectively. We believe a significant portion of the inconsistency between the 15N- and duodenal flow-derived data for microbial N incorporation into milk protein observed in the present study can be attributed to the inability of the duodenal techniques to fully account for the 15N-NAN of microbial origin reaching the small intestine and eventually used for milk protein synthesis.
Concentration of MUN reflects blood urea concentration and is in close relation to urinary N excretion in dairy cows (Jonker et al., 1998). The lowered MUN content when RFNDF was fed suggests more efficient utilization of dietary protein/ruminal ammonia with this diet compared to RFSS. Concentration of MUN varied greatly between cows and sampling times (Figure 3). This large variation once again questions the usefulness of spot- or individual cow-sampling for MUN analysis as an indicator of the N status of the cow (Hof et al., 1997; Trevaskis and Fulkerson, 1999).
|
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
|
ACKNOWLEDGEMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Corresponding author:
A. N. Hristov; email: ahristov{at}uidaho.edu.
Received for publication November 14, 2002. Accepted for publication January 24, 2003.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
-amino nitrogen by mixed ruminal microorganisms in vitro. Proceedings, Western Section, American Society of Animal Science, vol 48: 186–189.
This article has been cited by other articles:
|
|
 |
|
  S. I. Borucki Castro, L. E. Phillip, H. Lapierre, P. W. Jardon, and R. Berthiaume The Relative Merit of Ruminal Undegradable Protein from Soybean Meal or Soluble Fiber from Beet Pulp to Improve Nitrogen Utilization in Dairy Cows J Dairy Sci, October 1, 2008; 91(10): 3947 - 3957. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. N. Hristov Comparative characterization of reticular and duodenal digesta and possibilities of estimating microbial outflow from the rumen based on reticular sampling in dairy cows J Anim Sci, October 1, 2007; 85(10): 2606 - 2613. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. J. Suarez, C. G. Van Reenen, N. Stockhofe, J. Dijkstra, and W. J. J. Gerrits Effect of Roughage Source and Roughage to Concentrate Ratio on Animal Performance and Rumen Development in Veal Calves J Dairy Sci, May 1, 2007; 90(5): 2390 - 2403. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. E. Foley, A. N. Hristov, A. Melgar, J. K. Ropp, R. P. Etter, S. Zaman, C. W. Hunt, K. Huber, and W. J. Price Effect of barley and its amylopectin content on ruminal fermentation and nitrogen utilization in lactating dairy cows. J Dairy Sci, November 1, 2006; 89(11): 4321 - 4335. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. J. Suarez, C. G. Van Reenen, G. Beldman, J. van Delen, J. Dijkstra, and W. J. J. Gerrits Effects of supplementing concentrates differing in carbohydrate composition in veal calf diets: I. Animal performance and rumen fermentation characteristics. J Dairy Sci, November 1, 2006; 89(11): 4365 - 4375. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. N. Hristov, W. Hazen, and J. W. Ellsworth Efficiency of use of imported nitrogen, phosphorus, and potassium and potential for reducing phosphorus imports on idaho dairy farms. J Dairy Sci, September 1, 2006; 89(9): 3702 - 3712. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. F. Gressley and L. E. Armentano Effect of Abomasal Pectin Infusion on Digestion and Nitrogen Balance in Lactating Dairy Cows J Dairy Sci, November 1, 2005; 88(11): 4028 - 4044. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. N. Hristov, J. K. Ropp, K. L. Grandeen, S. Abedi, R. P. Etter, A. Melgar, and A. E. Foley Effect of carbohydrate source on ammonia utilization in lactating dairy cows J Anim Sci, February 1, 2005; 83(2): 408 - 421. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. N. Hristov, R. P. Etter, J. K. Ropp, and K. L. Grandeen Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows J Anim Sci, November 1, 2004; 82(11): 3219 - 3229. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. N. Hristov, K. L. Grandeen, J. K. Ropp, and M. A. McGuire Effect of Sodium Laurate on Ruminal Fermentation and Utilization of Ruminal Ammonia Nitrogen for Milk Protein Synthesis in Dairy Cows J Dairy Sci, June 1, 2004; 87(6): 1820 - 1831. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. P. Lundy III, E. Block, W. C. Bridges Jr., J. A. Bertrand, and T. C. Jenkins Ruminal Biohydrogenation in Holstein Cows Fed Soybean Fatty Acids as Amides or Calcium Salts J Dairy Sci, April 1, 2004; 87(4): 1038 - 1046. [Abstract] [Full Text] [PDF]
|
