J. Anim Sci.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kohn, R. A.
Right arrow Articles by Russek-Cohen, E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kohn, R. A.
Right arrow Articles by Russek-Cohen, E.
J. Anim. Sci. 2005. 83:879-889
© 2005 American Society of Animal Science

ANIMAL NUTRITION

Using blood urea nitrogen to predict nitrogen excretion and efficiency of nitrogen utilization in cattle, sheep, goats, horses, pigs, and rats1

R. A. Kohn2, M. M. Dinneen and E. Russek-Cohen

Department of Animal and Avian Sciences, University of Maryland, College Park 20742


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
The objectives of this study were to evaluate the potential for using blood urea N concentration to predict urinary N excretion rate, and to develop a mathematical model to estimate important variables of N utilization for several different species of farm animals and for rats. Treatment means (n = 251) from 41 research publications were used to develop mathematical relationships. There was a strong linear relationship between blood urea N concentration (mg/100 mL) and rate of N excretion (g•d–1•kg BW–1) for all animal species investigated. The N clearance rate of the kidney (L of blood cleared of urea•d–1•kg BW–1) was greater for pigs and rats than for herbivores (cattle, sheep, goats, horses). A model was developed to estimate parameters of N utilization. Driving variables for the model included blood urea N concentration (mg/100 mL), BW (kg), milk production rate (kg/d), and ADG (kg/d), and response variables included urinary N excretion rate (g/d), fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (N in milk and gain per unit of N intake). Prediction errors varied widely depending on the variable and species of animal, with most of the variation attributed to study differences. Blood urea N concentration (mg/100 mL) can be used to predict relative differences in urinary N excretion rate (g/d) for animals of a similar type and stage of production within a study, but is less reliable across animal types or studies. Blood urea N concentration (mg/100 mL) can be further integrated with estimates of N digestibility (g/g) and N retention (g/d) to predict fecal N (g/d), N intake (g/d), and N utilization efficiency (grams of N in milk and meat per gram of N intake). Target values of blood urea N concentration (mg/100 mL) can be backcalculated from required dietary N (g/d) and expected protein digestibility. Blood urea N can be used in various animal species to quantify N utilization and excretion rates.

Key Words: Blood Urea Nitrogen • Nitrogen Excretion • Nitrogen Utilization Efficiency


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Nitrogen losses from agriculture to air and water are perceived to be a major global environmental problem (NRC, 2003Go). Livestock farming is a significant source of reactive N in the environment. Of all the NH3 and N2O released into the environment because of human activity, approximately 70 and 30%, respectively, are estimated to arise from livestock farming (van Aardenne et al., 2001Go). The purpose of livestock farming is to convert the carbohydrates and proteins in animal feed to food sources for humans; however, only 5 to 30% of animal feed N usually meets this goal. The rest is excreted by animals and can escape into the environment.

The ability to estimate N excretion rate of animals might be used to minimize pollution as well as decrease the use of excess feed protein (NRC, 2003Go). For example, accurate estimates of manure N production rate may improve models to predict farm-level losses of N, and improve planning for manure handling. In addition, plasma or blood urea N (BUN) concentration may be useful as an indicator of protein status within a group of animals, and could help to fine-tune diets or identify problems with a feeding program. Milk urea N concentration is used to predict N excretion in dairy cows (Jonker et al., 1998Go; Kohn et al., 2002Go). Blood and plasma urea N concentration are proportional to milk urea N in dairy cows (Baker et al., 1995Go) and therefore may be useful as a predictor in much the same way. Differences in predictor values for various species may provide insight into differences in N utilization in these species.

Our first objective was to evaluate the potential for predicting urine N excretion rate (g/d) from BUN concentration (mg/100 mL) and BW (kg) for several domestic species. The second objective was to develop and evaluate a model to predict fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (grams of N in milk and gain per gram of N intake).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Implications
 Literature Cited
 
Published research data (Table 1Go) on several animal species were examined for N measurements, specifically rate of N intake (g/d), urinary N excretion rate (g/d), fecal N excretion rate (g/d), BUN concentration (mg/100 mL), and BW (kg). The species included beef and dairy cattle, goats, sheep, horses, pigs, and rats. Studies that included total urinary N excretion rate, BUN concentration, and BW or rate of N intake, fecal N excretion rate, and BW were included. Plasma urea N concentration was assumed to be equivalent to BUN concentration because urea diffuses freely into and out of blood cells. In some cases, fecal N excretion rate (g/d) was calculated from the reported apparent digestibility of protein (g/g) and intake N (g/d). The means (n = 251) from 41 research publications were analyzed. Table 2Go provides a summary of the data. Statistics were performed using JMP v. 5 (SAS Inst., Inc., Cary, NC), using the approach recommended by St-Pierre (2001)Go as described below.


View this table:
[in this window]
[in a new window]
  		Table 1. Dataset from the literature for development of the models
 

View this table:
[in this window]
[in a new window]
  		Table 2. Observational data for studies used to develop the models
 
Renal clearance rate is the rate at which blood is cleared completely of some substance by the kidney. The clearance rate of waste N (volume of blood cleared per unit time) was determined according to Swenson and Reece (1993)Go as:


where CR represents clearance rate (liters of blood cleared completely of urea per day), UN represents urinary N excretion rate (g/d), and BUN represents BUN concentration (g/L). Clearance rate was expressed as a fraction of BW because the animals used in the dataset varied in size. Kauffman and St-Pierre (2001)Go found that adjusting the coefficient to predict UN from milk urea N concentration with BW eliminated breed effects between Holsteins and Jerseys. We also considered expressing urinary N excretion rate as a fraction of metabolic BW (BW0.75), but fits were not improved, so results are not shown. The following statistical model was used within species:


where terms were as defined previously. Clearance rates were determined for all species as the regression coefficients for BUN. The intercept did not differ from zero for any species (BUN concentration = 0 implies urinary N excretion rate = 0) except cattle. Based on the physiology, we did not expect a significant intercept. Thus, the intercept was forced through zero for each species.

Fecal N was predicted using the Lucas test to calculate true digestibility (grams of N absorbed per gram of N intake) and metabolic N (g/d) from apparent digestibility with changing N intake (Van Soest, 1994Go). Apparent digestibility of N was defined by the equation:


where AD is apparent digestibility (g of N disappearance/g of intake N), NI is N intake (g/d), and FN is fecal N (g/d). True digestibility accounted for metabolic N as follows:


where TD is true digestibility (g of N digested/g of intake N), and M is metabolic fecal N (g/d). This equation was rearranged to yield:


where terms were as defined previously. To standardize the equation for animals of vastly different sizes, both sides were divided by metabolic BW in kilograms (BW0.75). The NRC (1996)Go calculates maintenance N, which includes endogenous N as a function of BW0.75 for beef cattle. In the present study, the parameters TD and M/BW0.75 were determined as the slope and intercept from regression analysis for each species using the statistical model:


where terms were as defined for previous equations.

The N retained per unit of ADG (g/kg) was also estimated by regression of grams of N retained against ADG in kilograms, with the intercept forced through 0 and study included as a random effect. This approach minimized the effect of animals growing at low rates of gain, where the N retained divided by ADG is highly unreliable.

There were limited data (109 means) that included all variables of interest for the same treatment means. When different model parameters are derived from different datasets and used together in a single prediction model, it is important that the relationships among variables are similar in both datasets. To evaluate whether data available for urea clearance rate estimates were equivalent to data available for digestibility estimates, additional statistical analyses were performed using only studies including all variables needed for both estimates, and these estimates were compared with those obtained by including all data (251 means) to make either estimate. Only results from the larger dataset are shown in tables, but other results are described when different.

Based on these estimates for urinary N excretion rate (g/d), true N digestibility (g/g), and N retention per unit of ADG (g/kg), the N intake (g/d), fecal N (g/d), and N utilization efficiency (g of N in milk and meat/g of N intake) were predicted as described in Table 3Go. These estimates were derived from the definitions of apparent and true digestibility and N utilization efficiency. The N utilization efficiency also was determined directly as the sum of N retained (g/d) in milk and gain divided by N intake (g/d).


View this table:
[in this window]
[in a new window]
  		Table 3. Model equations for prediction of nitrogen excretion
 
The accuracy of the model was evaluated by calculating the residuals (predicted – observed) for each observation (Bibby and Toutenburg, 1977Go). The root mean square prediction error (RMSPE) is composed of mean bias and residual error and is defined as:


For this study,


The mean of residuals was taken as the mean bias. The residual error, after accounting for mean bias, was computed by multiplying the standard deviation of residuals by {surd}[(n – 1)/n] to correct for the loss of 1 df due to fitting the mean when determining the standard deviation. This correction is required for small sample sizes. The fraction of variance attributed to mean bias was calculated as the mean bias squared divided by the mean square prediction error, and the fraction attributed to remaining dispersion was residual error2/mean square prediction error. Mean square prediction error attributed to the study effect was estimated as the partial sum of squares for the study divided by the sum of all partial sums of squares and the error sum of squares. Most studies are designed to minimize variation within study by using similar animals or the same animals, but this practice increases the possibility that the sample does not represent a broad population, and therefore, samples for different studies are likely to vary more from each other than from within studies.


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Implications
 Literature Cited
 
Nitrogen Clearance Rate
As expected, BUN concentration was linearly related to urinary N excretion rate for all species (Figure 1Go). The intercept of regression was not different from zero for any species except cattle (P < 0.05). The estimated N clearance rates (L of blood cleared of N•d–1•kg BW–1) for each species are shown in Table 4Go. Similar results (not shown) were obtained by directly calculating UN/(BW x BUN), but using the regression approach puts greater weight on higher values. This weighting is desirable because the values in which the BUN is close to 0 are less repeatable and skew the clearance rate estimates. For all species except rats, similar results were obtained when only using the limited dataset that included studies that reported all variables of interest, including those for both digestibility and clearance rates. Clearance rate averaged 4.8 L•d–1•kg BW–1 when using the complete dataset with all available data on rats (Table 4Go). However, clearance rate was 12.6 L•d–1•kg BW–1 for the limited dataset that included only seven means from the two studies with complete data (including digestibility data) for rats. The seven means yielding steep slopes can be identified in Figure 1Go for the rat data. Greater than 80% of the variance for random effects was attributed to studies for cattle, pigs, sheep, and rats (only one study was used for each of horses and goats), as shown in Table 4Go. This substantial study effect reflects differences in age and breed of animals, treatments, and analysis procedures. The results show the consistent relationship between BUN concentration and urinary N excretion rate, and the general coefficients that could be used to estimate urinary N excretion rate from blood measurements. Although these relationships held across studies and species, the relative difference within a study can be more consistently estimated than the differences across studies.



View larger version (29K):
[in this window]
[in a new window]
  		Figure 1. Urinary N (g•d–1•kg BW–1) vs. blood urea nitrogen (mg/100 mL) for each species. Data used for model development are shown with different symbols and lines representing different studies.

 

View this table:
[in this window]
[in a new window]
  		Table 4. Nitrogen clearance rate (L of blood cleared•d–1•kg BW–1) determined by regressiona
 
Estimates of urinary N (UN) could be calculated as:


where CR represents the calculated clearance rates. For a 500-kg cow, with a BUN of 0.20 g/L, and clearance rate of 1.3 (Table 3Go), UN would be 130 g/d (calculated as 1.3 x 0.2 x 500), but the confidence interval on the estimate would range from 89 to 171 g/d (calculated as: [1.3 ± 1.96 x SE] x 0.2 x 500) for an unknown study. However, the random effect of study contributes to most of this uncertainty. For comparisons within a study, the error would be substantially decreased. For example, for cattle, the SE within a study would be 0.05 (calculated as {surd}[SE2 x 0.08]), and the range with 95% confidence would be from 123 to 137 g/d.

To test differences in N clearance rates among species, ANOVA was performed on the clearance rates determined as regression coefficients for each study when regressing UN/BW on BUN. Data were transformed by taking the natural logarithm because variances were not equal across all species. The Levene test (JMP, v. 5) showed that unequal variances before transformation were corrected by transformation. Clearance rates differed among species according to the ANOVA conducted on the regression coefficients for each study (P < 0.001). Student’s t-tests revealed that the clearance rate for rats was higher than for all other species except pigs (P < 0.05), the clearance rates for pigs was higher (P < 0.05) than for sheep and goats, and others did not differ (P > 0.10). Figure 1Go shows that clearance rates for rats were similar to those of pigs for two of three studies using rats. Dairy and beef cattle data were combined because the estimates were not different among types of cattle (regression slopes ± 2 x SE overlapped).

The lower clearance rates for herbivores as compared with the omnivorous species may have resulted from divergent needs for each species due to the diets they have adapted to consume. Herbivores benefit from recycling of N to the gut from the blood, and thereby can survive on low amounts of low-quality protein. Nitrogen recycled to the rumen can be used to support fermentation and synthesis of microbial protein, whereas N recycled to the hindgut supports fermentation processes that provide energy, but do not supply protein to the animal. Keeping urea in the blood would be advantageous for herbivores, making greater levels of N recycling to the gut possible. The omnivores, on the other hand, have a greater need to excrete N, which may become toxic to them. For all species, the blood urea concentrations were in the same range regardless of the quantity of protein consumed (Table 2Go). The poorer fit of data to the regression lines within rat studies may have resulted from the use of completely randomized designs for rat studies rather than designs with treatments nested within animal as was the case for the other species.

Digestibility
True digestibility and metabolic fecal N are shown for each species in Table 5Go and the relevant regression equations are shown in Figure 2Go. For all species except rats, similar results also were obtained when only using studies that reported variables for both digestibility and clearance rates. When using all the data available for N digestibility in rats, the true digestibility was only 79% (Table 5Go); however, true digestibility was 99% for the seven means with complete data for rats. These differences for the limited vs. complete datasets for rats may be attributed to the small sample size in both cases. With both datasets, metabolic N was not significantly different from zero for rats. The lower magnitude of metabolic fecal N for pigs and rats may result from the lower amount of microbial residues in the feces and less complex system of protein and fiber digestion. High true digestibility of N and the large variance in digestibility reflect the diverse types of protein sources used in these studies, as well as the diverse types of animals. Use of mature forages for several studies with cattle resulted in decreased protein digestibility. The digestibility in these studies seems similar to that assumed by diet formulation recommendations (NRC, 1996Go, 2001Go).


View this table:
[in this window]
[in a new window]
  		Table 5. True crude protein digestibility (%) and metabolic fecal N (g/kg BW0.75) calculated for different species by regressiona
 


View larger version (25K):
[in this window]
[in a new window]
  		Figure 2. Apparent N absorbed (g•d–1•kg BW–0.75) vs. N intake (g•d–1•kg BW–0.75) for each species. The slope represents true digestibility (%), and the y-intercept is the negative value of metabolic fecal N (g/kg BW0.75). Data used for model development are shown with different symbols and lines representing different studies.

 
Nitrogen Retention
For species in which data were available, the N retention per kilogram BW was determined as shown in Table 6Go. These values were slightly higher than reported using changes in carcass N. In those studies, retained N ranged from 14 to 16 g/kg for swine (Mahan and Shields, 1998Go) and 20 to 22 g/kg for beef cattle (Ferrell and Jenkins, 1998Go). Retained N in balance studies, like the ones used in the present analysis, is determined by difference between N intake and output, so that losses, including volatilization of fecal or urinary N during collection, are considered part of the retention. Hence, these procedures may overestimate N retention compared with results from slaughter studies.


View this table:
[in this window]
[in a new window]
  		Table 6. Nitrogen retained in grams per kilogram of average daily live weight gain determined by regression for different speciesa
 
Nitrogen Utilization Predictions
The purpose of deriving these parameters was to determine the feasibility of using BUN and production data to estimate values of interest in modeling herd or flock N utilization, and whole-farm N losses. The mean excretion and efficiency predictions for each species, the RMSPE, and the components of variation in the error are shown in Table 7Go. In this case, the coefficients reported in the previous tables were used to make estimates for all cases where data were available to evaluate the estimates. The RMSPE varied from 7 to 112% of the mean estimate for urinary N excretion rate, but most of this variation was attributed to study differences. The substantial mean bias for cattle resulted from forcing the intercept of the line through zero for the clearance rate estimate. There is no physiological reason to explain a significant intercept, and it was not significant for data from other species. Prediction errors for rate of N intake and fecal N excretion rate also were largely attributed to differences among studies. Substantial variation was attributed to mean bias in cases where the residual analysis could only use a small subset of the data that were used in model development. In essence, this effect was also a bias imposed by study differences. Because most of the error in predictions was attributed to study differences, the proposed model is likely to be a better tool to detect relative differences within studies with similar animals and diets, than to determine absolute estimates of N utilization. Much of the variation in predictions was due to imposed treatments that varied greatly in N digestibility to a degree that may exceed what would be observed on commercial farms.


View this table:
[in this window]
[in a new window]
  		Table 7. Partitioning of root mean square prediction error (RMSPE) for each animal species
 
This study demonstrates the feasibility of using BUN concentration to predict N excretion rate for various domestic animals. With adequate estimates of N digestibility, one can also determine rate of N intake, fecal N excretion rate, and N utilization efficiency (grams of N in milk and gain per gram of N intake). A similar approach using milk urea N concentration was used to characterize herd N utilization and excretion on 450 commercial dairy farms (Jonker et al., 2002aGo). By estimating the urinary N excretion rate that is expected when feeding recommended quantities of protein, one can back-calculate target BUN concentrations for given production rates. This approach has been taken for milk urea N concentration (Jonker et al., 1999Go), and farms that miss this target can be identified for assistance. An extension program using milk urea N concentration in this way was able to document changes in management resulting in decreased feed costs (Jonker et al., 2002bGo).


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
Literature Cited
 
Concentration of blood urea nitrogen was highly correlated with urinary nitrogen excretion rate. Blood samples may enable prediction of nitrogen excretion rate, and subsequently fecal nitrogen excretion rate, rate of nitrogen intake, and nitrogen utilization efficiency (nitrogen in milk and gain per nitrogen intake). Target blood urea nitrogen concentration can be calculated for different species for different production rates. Herbivorous species (cattle, sheep, goats, and horses) had lower nitrogen clearance rates than pigs and rats. Herbivores have adapted to conserving urea nitrogen for recycling to the gut, which may explain the lower nitrogen clearance rates.


   Footnotes
 
1 A contribution from the Maryland Agric. Exp. Stn. Back

2 Correspondence: Animal Sciences Building, #142 (phone: 301-405-4583; fax: 301-314-9059; e-mail: rkohn{at}umd.edu).

Received for publication August 4, 2004. Accepted for publication January 4, 2005.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 


Ahmad, M. R., V. G. Allen, J. P. Fontenot, and G. W. Hawkins. 1995. Effect of sulfur fertilization on chemical composition, ensiling characteristics, and utilization by lambs of sorghum silage. J. Anim. Sci. 73:1803–1810.[Abstract]

Alawa, J. P. 1991. Nitrogen excretion by sheep fed low-protein roughage diets. Small Rumin. Res. 6:279–284.

Archibeque, S. L., J. C. Burns, and G. B. Huntington. 2001. Urea flux in beef steers: Effects of forage species and nitrogen fertilization. J. Anim. Sci. 79:1937–1943.[Abstract/Free Full Text]

Archibeque, S. L., J. C. Burns, and G. B. Huntington. 2002. Nitrogen metabolism of beef steers fed endophyte-free tall fescue hay: Effects of ruminally protected methionine supplementation. J. Anim. Sci. 80:1344–1351.[Abstract/Free Full Text]

Bailey, C. B. 1989. Rate and efficiency of gain, body composition, nitrogen, metabolism, and blood composition of growing Holstein steers given diets of roughage or concentrate. J. Anim. Sci. 69:707–725.

Baker, L. D., J. D. Ferguson, and W. Chalupa. 1995. Responses in urea and true protein of milk to different protein feeding schemes for dairy cows. J. Dairy Sci. 78:2424–2434.[Abstract]

Betrán, M. A., E. Estornell, T. Barber, and J. Cabo. 1992. Nitrogen metabolism in obesity induced by monosodium-L-glutamate in rats. Int. J. Obes. 16:555–564.[Medline]

Bibby, J., and H. Toutenburg. 1977. Pages 16–19 in Prediction and Improved Estimation in Linear Models. John Wiley & Sons, London, U.K.

Bohnert, D. W., B. T. Larson, S. J. Lewis, C. J. Richards, K. C. Swanson, D. L. Harmon, and G. E. Mitchell, Jr. 1999. Net nutrient flux in visceral tissues of lambs fed diets differing in supplemental nitrogen source. J. Anim. Sci. 77:2545–2553.[Abstract/Free Full Text]

Cole, N. A. 1999. Nitrogen retention by lambs fed oscillating dietary protein. J. Anim. Sci. 77:215–222.[Abstract/Free Full Text]

Dinn, N. E., J. A. Shelford, and L. J. Fisher. 1998. Use of the Cornell Net Carbohydrate and Protein System and rumen-protected lysine and methionine to reduce nitrogen excretion from lactating dairy cows. J. Dairy Sci. 81:229–237.[Abstract]

Dunn, J. M., and V. C. Speer. 1991. Nitrogen requirement of pregnant gilts. J. Anim. Sci. 69:2020–2025.[Abstract]

Estermann, B. L., F. Sutter, P. O. Schlegel, D. Erdin, H. R. Wettstein, and M. Kreuzer. 2002. Effect of calf age and dam breed on intake, energy expenditure, and excretion of nitrogen, phosphorus, and methane of beef cows with calves. J. Anim. Sci. 80:1124–1134.[Abstract/Free Full Text]

Esteve, M., I. Rafecas, X. Remesar, and M. Alemany. 1992. Nitrogen balance of lean and obese Zucker rats subjected to a cafeteria diet. Int. J. Obes. 16:237–244.[Medline]

Ferrell, C. L., and T. G. Jenkins. 1998. Body composition and energy utilization by steers of diverse genotypes fed a high-concentrate diet during the finishing period: I. Angus, Belgian Blue, Hereford, and Piedmontese Sires. J. Anim. Sci. 76:637–646.[Abstract/Free Full Text]

Ferrell, C. L., K. K. Kreikemeier, and H. C. Freetly. 1999. The effect of supplemental energy, nitrogen, and protein on feed intake, digestibility, and nitrogen flux across the gut and liver in sheep fed low-quality forage. J. Anim. Sci. 77:3353–3364.[Abstract/Free Full Text]

Fisher, L. J., N. E. Dinn, J. A. Shelford, and J. W. Paul. 2000. The effect of concentration and form of dietary nitrogen on the utilization and excretion of nitrogen by lactating dairy cows. Can. J. Anim. Sci. 80:207–209.

Forster, L. A., J. P. Fontenot, H. D. Perry, J. G. Foster, and V. G. Allen. 1991. Apparent digestibility and nutrient balance in lambs fed different levels of flatpea hay. J. Anim. Sci. 69:1719–1725.[Abstract]

Haig, P. A., T. Mutsvangwa, R. Spratt, and B. W. McBride. 2002. Effects of dietary protein solubility on nitrogen losses from lactating dairy cows and comparison with predictions from the Cornell Net Carbohydrate and Protein System. J. Dairy Sci. 85:1208–1217.[Abstract]

Harmuth-Hoene, A. E., and E. Schwerdtfeger. 1979. Effect of indigestible polysaccharides on protein digestibility and nitrogen retention in growing rats. Nutr. Metab. 23:399–407.[Medline]

Hettiarachchi, M., R. M. Dixon, and J. V. Nolan. 1999. Effect of intra-ruminal urea infusions and changing digestible organic matter intake on nitrogen kinetics in sheep fed rice straw. J. Agric. Sci. (Camb.) 133:109–121.

Hoffman, P. C., N. M. Esser, L. M. Bauman, S. L. Denzine, M. Engstrom, and H. Chester-Jones. 2001. Effect of dietary protein on growth and nitrogen balance of Holstein heifers. J. Dairy Sci. 84:843–847.[Abstract]

Huntington, G. B. 1984. Net absorption of glucose and nitrogenous compounds by lactating Holstein cows. J. Dairy Sci. 67:1919–1927.[Abstract/Free Full Text]

Jonker, J. S., R. A. Kohn, and R. A. Erdman. 1998. Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cows. J. Dairy Sci. 81:2681–2692.[Abstract]

Jonker, J. S., R. A. Kohn, and R. A. Erdman. 1999. Milk urea nitrogen target concentrations for lactating dairy cows fed according to National Research Council recommendations. J. Dairy Sci. 82:1261–1273.[Abstract]

Jonker, J. S., R. A. Kohn, and J. High. 2002a. Dairy herd management practices that impact nitrogen utilization efficiency. J. Dairy Sci. 85:1218–1226.[Abstract]

Jonker, J. S., R. A. Kohn, and J. High. 2002b. Use of milk urea nitrogen to improve diary cows diets. J. Dairy Sci. 85:939–946.[Abstract]

Kaiser, A. G., D. F. Osbourn, and P. England. 1983. Intake, digestion and nitrogen retention by calves given ryegrass silages: Influence of formaldehyde treatment and supplementation with maize starch or maize starch and urea. J. Agric. Sci. (Camb.) 100:63–74.

Kauffman, A. J., and N. R. St-Pierre. 2001. The relationship of milk urea nitrogen to urine nitrogen excretion in Holstein and Jersey cows. J. Dairy Sci. 84:2284–2294.[Abstract]

Knaus, W. F., D. H. Beerman, T. F. Robinson, D. G. Fox, and K. D. Finnerty. 1998. Effects of dietary mixture of meat and bone meal, feather meal, blood meal, and fishmeal on nitrogen utilization in finishing Holstein steers. J. Anim. Sci. 76:1481–1487.[Abstract/Free Full Text]

Koenig, J. M., N. W. Bradley, and J. A. Boling. 1982. Liver arginase activity and urea metabolism in beef heifers fed urea diets and abomasally infused with arginine and(or) ammonium acetate. J. Anim. Sci. 54:426–433.[Abstract/Free Full Text]

Kohn, R. A., K. F. Kalscheur, and E. Russek-Cohen. 2002. Evaluation of models to estimate urinary nitrogen and expected milk urea nitrogen. J. Dairy Sci. 85:227–233.[Abstract]

Köster, H. H., R. C. Cochran, E. C. Titgemeyer, E. S. Vanzant, T. G. Nagaraja, K. K. Kreikemeier, and G. St. Jean. 1997. Effect of increasing proportion of supplemental nitrogen from urea on intake and utilization of low-quality, tallgrass-prairie forage by beef steers. J. Anim. Sci. 75:1393–1399.[Abstract/Free Full Text]

Lindberg, J. E. 1989. Nitrogen metabolism and urinary excretion of purines in goat kids. Brit. J. Nutr. 61:309–321.[Medline]

Lykos, T., G. A. Varga, and D. Casper. 1997. Varying degradation rates of total nonstructural carbohydrates: Effects on ruminal fermentation, blood metabolites and milk production and composition in high-producing Holstein cows. J. Dairy Sci. 80:3341–3355.[Abstract]

Mahan, D. C., and R. G. Shields, Jr. 1998. Macro- and micro-mineral composition of pigs from birth to 145 kilograms of body weight. J. Anim. Sci. 76:506–512.[Abstract/Free Full Text]

Martin, R. G., N. P. McMeniman, B. W. Norton, and K. F. Dowsett. 1996. Utilization of endogenous and dietary urea in the large intestine of the mature horse. Br. J. Nutr. 76:373–386.[Medline]

Mosenthin, R., W. C. Sauer, and C. F. M. de Lange. 1992a. Tracer studies of urea kinetics in growing pigs. I. The effect of intravenous infusion of urea on urea recycling and the site of urea secretion into gastrointestinal tract. J. Anim. Sci. 70:3458–3466.[Abstract]

Mosenthin, R., W. C. Sauer, H. Henkel, F. Ahrens, and C. F. M. de Lange. 1992b. Tracer studies of urea kinetics in growing pigs. II. The effect of starch infusion at the distal ileum on urea recycling and bacterial nitrogen excretion. J. Anim. Sci. 70:3467–3472.[Abstract]

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC.

NRC. 2001. Nutrient Requirements of Dairy Cattle. 7th ed. Natl. Acad. Press, Washington, DC.

NRC. 2003. Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs. Natl. Acad. Press, Washington, DC.

Rubio, L. A., G. Grant, P. Dewey, D. Brown, M. Annand, S. Bardocz, and A. Pustai. 1998. Nutritional utilization by rats of chickpea (Cicer arietinum) meal and its isolated globulin proteins is poorer than that of defatted soybean or lactalbumin. J. Nutr. 128:1042–1047.[Abstract/Free Full Text]

Smith, S. I., and J. A. Boling. 1984. Lipid coating as a mode of protecting free methionine from ruminal degradation. J. Anim. Sci. 58:187–193.[Abstract/Free Full Text]

St-Pierre, N. R. 2001. Integrating quantitative findings from multiple studies using mixed model methodology. J. Dairy Sci. 84:741–755.[Abstract]

Swenson, M. J. and W. O. Reece. 1993. Water balance and excretion. Pages 573–604 in Duke’s Physiology of Domestic Animals. 11th ed. Cornell Univ. Press, Ithaca, NY.

Sutoh, M., Y. Obara, and T. Yoneyama. 1993. The effects of feeding regimen and dietary sucrose supplementation on natural abundance of 15N in some components of ruminal fluid and plasma of sheep. J. Anim. Sci. 1993. 71:226–231.[Abstract]

Theurer, C. B., G. B. Huntington, J. T. Huber, R. S. Swingle, and J. A. Moore. 2002. Net absorption and utilization of nitrogenous compounds across ruminal, intestinal, and hepatic tissues of growing beef steers fed dry-rolled or steam-flaked sorghum grain. J. Anim. Sci. 80:525–532.[Abstract/Free Full Text]

van Aardenne, J. A., F. J. Dentener, C. G. M. Klijn Goldewijk, J. Lelieveld, and J. G. J. Olivier. 2001. A 1°–1° resolution dataset of historical anthropogenic trace gas emissions for the period 1890–1990. Global Biogeochem. Cycles 15:909–920.

Van Barneveld, R. J., E. S. Batterham, and D. C. Skingle. 1995. The effect of heat on amino acids for growing pigs. 4. Nitrogen balance and urine, serum, and plasma composition of growing pigs fed on raw or heat-treated field peas (Pisum sativum). Br. J. Nutr. 73:259–273.[Medline]

Van Soest, P. J. 1994. Nutritional Ecology of the Ruminant. 2nd ed. Cornell Univ. Press, Ithaca, NY.

Verstegen, M. W. A., D. Zwart, W. van der Hel, B. O. Brouwer, and T. Wensing. 1991. Effect of Tryppanosoma vivax infection on energy and nitrogen metabolism of west African dwarf goats. J. Anim. Sci. 69:1667–1677.[Abstract]

Woodward, A., and J. D. Reed. 1997. Nitrogen metabolism of sheep and goats consuming Acacia brevispica and Sesbania sesban. J. Anim. Sci. 75:1130–1139.[Abstract/Free Full Text]

Younes, H., C. Demigne, S. R. Behr, K. A. Garleb, and C. Remesy. 1996. A blend of dietary fibers increases urea disposal in the large intestine and lowers urinary nitrogen excretion in rats fed a low protein diet. J. Nutr. Biochem. 7:474–480.

Younes, H., K. A. Garleb, S. R. Behr, C. Demigne, and C. Remesy. 1998. Dietary fiber stimulates the extra-renal route of nitrogen excretion in partially nephrectomized rats. J. Nutr. Biochem. 9:613–620.

Zerves, S., and R. T. Zijlstra. 2002a. Effects of dietary protein and fermentable fiber on nitrogen excretion patterns and plasma urea in grower pigs. J. Anim. Sci. 80:3247–3256.[Abstract/Free Full Text]

Zerves, S., and R. T. Zijlstra. 2002b. Effects of dietary protein and oathull fiber on nitrogen excretion patterns and postprandial plasma urea profiles in grower pigs. J. Anim. Sci. 80:3238–3246.[Abstract/Free Full Text]


This article has been cited by other articles:


Home page
 J ANIM SCIHome page
J. C. Marini, D. G. Fox, and M. R. Murphy
Nitrogen transactions along the gastrointestinal tract of cattle: A meta-analytical approach
J Anim Sci, March 1, 2008; 86(3): 660 - 679.
[Abstract] [Full Text] [PDF]

Home page
 J. Environ. Qual.Home page
D. M. Butler, N. N. Ranells, D. H. Franklin, M. H. Poore, and J. T. Green Jr.
Ground Cover Impacts on Nitrogen Export from Manured Riparian Pasture
J. Environ. Qual., January 9, 2007; 36(1): 155 - 162.
[Abstract] [Full Text] [PDF]

Home page
 J. Environ. Qual.Home page
D. M. Butler, D. H. Franklin, N. N. Ranells, M. H. Poore, and J. T. Green Jr.
Ground Cover Impacts on Sediment and Phosphorus Export from Manured Riparian Pasture
J. Environ. Qual., October 27, 2006; 35(6): 2178 - 2185.
[Abstract] [Full Text] [PDF]

Home page
 J. Environ. Qual.Home page
X. Hao, P. S. Mir, M. A. Shah, and G. R. Travis
Influence of Canola and Sunflower Diet Amendments on Cattle Feedlot Manure
J. Environ. Qual., July 5, 2005; 34(4): 1439 - 1445.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kohn, R. A.
Right arrow Articles by Russek-Cohen, E.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kohn, R. A.
Right arrow Articles by Russek-Cohen, E.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS