The Degradation and Utilization of Endogenous Urea in the Gastrointestinal Tract of Ruminants: A Review

Kennedy, P. M.; Milligan, L. P.

doi:10.4141/cjas80-030

Cited by 245 publications

(173 citation statements)

References 10 publications

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“…It is also possible that tannins might decrease the entry rate of urea through the digestive tract. In conventional diets, EUN follows an opposite behaviour of MFN (37) , which might be attributable to urea recycling to the large intestine being enhanced by increasing hindgut fermentation with increasing NI (43,47) and increased concentrations of ammonia in the rumen (38) . The metabolisable protein requirement of sheep estimated from total basal N excretion i.e.…”

Section: Endogenous Nitrogen Lossesmentioning

confidence: 96%

“…In ruminants, a number of factors such as intakes of N, DM and digestible OM, ammonia concentration in the rumen and dietary NDF concentration influence the extent of urea N recycling to the gastrointestinal tract and MFN excretion. Kennedy & Milligan (38) proposed that urea recycling to the rumen increases when digestible OM intake increases and/or ruminal ammonia concentration decreases. Giraldez et al (37) clearly demonstrated that MFN increased quadratically from 153 to 280 mg/kg W 0·75 with increasing levels of digestible OM intake by sheep, which had been explained due to increased N entry to the gastrointestinal tract.…”

Section: Endogenous Nitrogen Lossesmentioning

confidence: 99%

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Aspects of nitrogen metabolism in sheep-fed mixed diets containing tree and shrub foliages

Patra

2009

Br J Nutr

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Data on N utilisation by sheep-fed diets containing foliages were analysed to develop prediction equations for N excretion in faeces (FN) and urine (UN), and to determine endogenous N excretion. Overall, 218 dietary treatments from forty-four publications were compiled in the database. This database was split into three subsets: without foliage in the diets (FL-0); foliage levels (FL) in between 0 and 310 g/kg (FL-L); FL in between 310 and 800 g/kg diets (FL-H) to study the effects of foliages on metabolic faecal N (MFN) and endogenous urinary N (EUN). Nitrogen intake (NI) as single independent factor was the best predictor of FN (R 2 0·75), UN (R 2 0·81) and total N excretion (R 2 0·86). Addition of dietary N concentration and FL for FN (R 2 0·82), dietary N concentration and foliage NI for UN (R 2 0·85), and FL and foliage NI for total N excretion (R 2 0·92) as supporting predictors to this relationship slightly increased R 2 values. The monomolecular and exponential models slightly improved the prediction of N excretion with NI as a predictor compared with the linear model. The excretion of MFN was greater for FL-H compared with FL-0, but was similar between FL-0 and FL-L, and FL-L and FL-H. However, EUN decreased in FL-H compared with FL-0 and FL-L, but was similar between FL-0 and FL-L. In conclusion, using NI as the primary predictor produced an accurate prediction of N excretion. Inclusion of foliages in the diets may shift N excretion from urine to faeces and increase the excretion of MFN and EUN. Tree foliage: Nitrogen metabolism: Prediction model: Endogenous nitrogen: SheepFoliages from trees and browses are the important feed resources for small ruminant production (1 -3) to enhancing the productivity of animals. Fodder trees are more particularly important in the arid and semi-arid regions because trees can survive harsh climatic conditions compared to grasses, and hence may be more reliable feed resources in these areas. These multipurpose tree foliages contain moderate levels of N, minerals and vitamins (1,2) , and have been suggested as a solution to feeding of ruminants in the tropical areas, especially as supplementary feeds to low-quality forages (3 -6) .Many models have been published, particularly in recent years, in an effort to reduce N excretion in the environment, to develop prediction equations for N excretion in faeces and urine and to increase the efficiency of utilisation of dietary N in dairy and beef cattle based on the dietary chemical composition (7 -11) , and sheep and goats based on blood urea N levels (12) . Although tree leaves contain moderate level of N, they also contain tannins and other secondary compounds that may influence intake and utilisation of nutrients. In particular, tannins bind dietary protein, which might affect N excretions and retention, thus affecting protein utilisation patterns. For instance, it has been proposed that foliages containing tannins could increase the excretion of metabolic faecal N (4) , and alter the N partitioning between faecal and uri...

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Section: Endogenous Nitrogen Lossesmentioning

confidence: 96%

Section: Endogenous Nitrogen Lossesmentioning

confidence: 99%

Aspects of nitrogen metabolism in sheep-fed mixed diets containing tree and shrub foliages

Patra

2009

Br J Nutr

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“…In ruminants, significant amounts of urea formed in the liver can be transferred to the rumen (Kowalczyk et al, 1975a,b;Harmeyer and Martens, 1980;Kennedy and Milligan, 1980). Urea is then hydrolysed in the rumen (Gibbons and McKarthy, 1957) and the resulting ammonia is utilized by rumen bacteria as an important source of nitrogen for protein synthesis (Gärtner et al, 1961;Virtanen, 1964;Bunting et al, 1989).…”

Section: Introductionmentioning

confidence: 99%

Incorporation of endogenous urea nitrogen into the amino acids of bacterial protein in the rumen of goats fed diets with various protein levels

Michalski¹,

Kowalczyk²,

Czauderna³

et al. 2013

J. Anim. Feed Sci.

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“…Urea N recycling and assimilation by ruminal microbes are influenced by dietary and ruminal factors, and intakes of CP and digestible organic matter (OM) are major factors (Harmeyer and Martens, 1980;Kennedy and Milligan, 1980). A better understanding of the relationships between dietary factors and urea kinetics and microbial usage of recycled urea would allow for a more accurate estimation of N supply and N requirements by current feeding models.…”

mentioning

confidence: 99%

“…Ruminal NH 3 concentration, DOM and PUN concentration are the principal factors affecting urea recycling from blood to the lumen of the GIT (Kennedy and Milligan, 1980). Ruminal concentrations of NH 3 and OM digestion tend to be inversely related to each other, whereas GER is negatively related to ruminal NH 3 concentration, and positively related to PUN concentration.…”

mentioning

confidence: 99%

The effect of CP concentration in the diet on urea kinetics and microbial usage of recycled urea in cattle: a meta-analysis

Batista

Detmann

Filho

et al. 2017

Animal

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In ruminants, urea recycling is considered an evolutionary advantage. The amount of urea recycled mainly depends of the nitrogen (N) intake and the amount of organic matter (OM) digested in the rumen. Because recycled N contributes to meeting microbial N requirements, accurate estimates of urea recycling can improve the understanding of efficiency of N utilization and N losses to the environment. The objective of this study was to evaluate urea kinetics and microbial usage of recycled urea N in ruminants using a meta-analytical approach. Treatment mean values were compiled from 25 studies with ruminants (beef cattle, dairy cows and sheep) which were published from 2001 to 2016, totalling 107 treatment means. The data set was analyzed according to meta-analysis techniques using linear or non-linear mixed models, taking into account the random variations among experiments. Urea N synthesized in the liver (UER) and urea N recycled to the gut (GER) linearly increased (P < 0.001) as N intake (g/BW 0.75 ) increased, with increases corresponding to 71.5% and 35.2% of N intake, respectively. The UER was positively associated (P < 0.05) with dietary CP concentration and the ratio of CP to digestible OM (CP:DOM). Maximum curvature analyses identified 17% dietary CP as the point where there was a prominent increase in hepatic synthesis of urea N, likely due to an excess of dietary N leading to greater ammonia absorption. The GER:UER decreased with increasing dietary CP concentration (P < 0.05). At dietary CP ⩾ 19%, GER:UER reached near minimal values. The fraction of UER eliminated as urinary urea N and the contribution of urea N to total urinary N were positively associated with dietary CP ( P < 0.05), both reaching values near the plateau when dietary CP was 17%. The fractions of GER excreted in the feces and utilized for anabolism decreased, whereas the fraction of GER returned to the ornithine cycle increased with dietary CP concentration (P < 0.05). Recycled urea N assimilated by ruminal microbes (as a fraction of GER) decreased as dietary CP and CP:DOM increased (P < 0.05). The efficiency of microbial assimilation of recycled urea N was near plateau values at 194 g CP/kg DOM. The models obtained in this study contribute to the knowledge on N utilization, and they could be used in feeding models to predict urea recycling and thus to improve formulation of diets to reduce N losses that contribute to air and water pollution.Keywords: cattle, mixed models, protein, recycling, ruminal bacteria ImplicationsIn cattle systems, many farmers utilize feeding models to estimate protein requirements. However, most models recognize the importance of urea nitrogen (N) recycling in the rumen, but not all account for it. In such situation, a tendency to oversupply dietary CP may occur, leading to higher feed costs and N excretion. As N excreted can contribute to air and water pollution, more efficient feeding strategies are required to maximize N utilization. In this study, we used a meta-analytical approach to obtain models that cou...

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The Degradation and Utilization of Endogenous Urea in the Gastrointestinal Tract of Ruminants: A Review

Abstract: For personal use only.

Cited by 245 publications

References 10 publications

Aspects of nitrogen metabolism in sheep-fed mixed diets containing tree and shrub foliages

Aspects of nitrogen metabolism in sheep-fed mixed diets containing tree and shrub foliages

Incorporation of endogenous urea nitrogen into the amino acids of bacterial protein in the rumen of goats fed diets with various protein levels

The effect of CP concentration in the diet on urea kinetics and microbial usage of recycled urea in cattle: a meta-analysis

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