Metabolic implications of ammonia production in the ruminant

Parker, David S.; Lomax, M.A.; Seal, CJ; Wilton, J.

doi:10.1079/pns19950023

Cited by 92 publications

(79 citation statements)

References 68 publications

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“…Both ammonia and ammonium are transported across the rumen epithelium (Bö deker and Kemkowski, 1996) and the net portal uptake of ammonia is important and makes a substantial contribution to the total N input for hepatic urea synthesis (Parker et al, 1995). Given the relatively high absorbability of ammonia, maintaining the minimum ruminal ammonia concentration turns out to be expensive to the ruminant in terms of energy input to resynthesize urea, but it also poses a challenge to N efficiency.…”

Section: Impact Of N Recycling On the Efficiency Of N Utilization In mentioning

confidence: 99%

Strategies for optimizing nitrogen use by ruminants

Calsamiglia

Ferret

Reynolds

et al. 2010

Animal

235

165

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The efficiency of N utilization in ruminants is typically low (around 25%) and highly variable (10% to 40%) compared with the higher efficiency of other production animals. The low efficiency has implications for the production performance and environment. Many efforts have been devoted to improving the efficiency of N utilization in ruminants, and while major improvements in our understanding of N requirements and metabolism have been achieved, the overall efficiency remains low. In general, maximal efficiency of N utilization will only occur at the expense of some losses in production performance. However, optimal production and N utilization may be achieved through the understanding of the key mechanisms involved in the control of N metabolism. Key factors in the rumen include the efficiency of N capture in the rumen (grams of bacterial N per grams of rumen available N) and the modification of protein degradation. Traditionally, protein degradation has been modulated by modifying the feed (physical and chemical treatments). Modifying the rumen microflora involved in peptide degradation and amino acid deamination offers an alternative approach that needs to be addressed. Current evidence indicates that in typical feeding conditions there is limited net recycling of N into the rumen (blood urea-N uptake minus ammonia-N absorption), but understanding the factors controlling urea transport across the rumen wall may reverse the balance to take advantage of the recycling capabilities of ruminants. Finally, there is considerable metabolism of amino acids (AA) in the portal-drained viscera (PDV) and liver. However, most of this process occurs through the uptake of AA from the arterial blood and not during the 'absorptive' process. Therefore, AA are available to the peripheral circulation and to the mammary gland before being used by PDV and the liver. In these conditions, the mammary gland plays a key role in determining the efficiency of N utilization because the PDV and liver will use AA in excess of those required by the mammary gland. Protein synthesis in the mammary gland appears to be tightly regulated by local and systemic signals. The understanding of factors regulating AA supply and absorption in the mammary gland, and the synthesis of milk protein should allow the formulation of diets that increase total AA uptake by the mammary gland and thus reduce AA utilization by PDV and the liver. A better understanding of these key processes should allow the development of strategies to improve the efficiency of N utilization in ruminants. Keywords: ruminant, nitrogen efficiency ImplicationsRuminants have a low efficiency of N utilization compared with non-ruminants. This low efficiency has implications not only for production performance and economic efficiency but also for the emission of contaminants to the environment. The efficiency of N utilization can be improved through the understanding and modification of factors regulating the efficiency of N utilization in key processes, including N capture in the rumen, ...

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Section: Impact Of N Recycling On the Efficiency Of N Utilization In mentioning

confidence: 99%

Strategies for optimizing nitrogen use by ruminants

Calsamiglia

Ferret

Reynolds

et al. 2010

Animal

235

165

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“…The utilization of amino acids for urea synthesis could be increased when there is an increased occurrence of the urea cycle (LOBLEY et al, 1995) and could be associated with low nitrogen retention in the bodies of ruminants fed forage-based diets (PARKER et al, 1995). Marini and Van Amburgh (2003) reported that an improvement in nitrogen supply increased the liver synthesis of urea from dietary urea (which could indirectly indicate a decrease in the utilization of other sources for urea synthesis, such as amino acids).…”

Section: Item Experimentsmentioning

confidence: 99%

“…The pools for mitochondrial and cytoplasm transamination are normally under equilibrium, and so the two nitrogen atoms of urea may come from ammonia or from amino acids by the reversible action of glutamate dehydrogenase. However, under a high urea flow or demand, the mitochondrial ammonia is not sufficient to supply both nitrogen atoms resulting in an increased utilization of amino acids for urea synthesis (PARKER et al, 1995).…”

Section: Item Experimentsmentioning

confidence: 99%

Nutritional aspects applied to grazing cattle in the tropics: a review based on Brazilian results

et al. 2014

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This review presents and discusses the nutritional and physiological aspects of cattle production under grazing in the tropics. The critical evaluations were based on Brazilian experimental results as well as on basic literature concerning ruminant nutrition. Several associations between the characteristics of the grazed forage, the composition of the supplements and animal and microbial requirements were established. The adopted approach was divided according to two different climatic seasons observed in the tropics: dry and rainy seasons. During the dry season, the main nutritional constraints on animal performance are associated with inherent requirements of the rumen fibrolytic microorganisms. An overall deficiency of nitrogenous compounds is observed in the forage, which compromises forage intake and digestibility. Supplementation with nitrogenous compounds must be a priority in this season to increase forage intake and energy extraction from forage fiber. However, during the rainy season, no constraints on microbial growth are observed. The usual pasture composition presents an unbalanced and high ratio of energy to protein when compared to animal requirements. In such cases, protein supplementation is needed to equilibrate the basal diet and improve the utilization of metabolizable energy and protein.Key words: Cattle production, supplementation, ruminant metabolism, tropical forages ResumoA presente revisão baseia-se na apresentação e discussão dos aspectos nutricionais da produção de bovinos em pastejo nos trópicos. As avaliações críticas foram calcadas em resultados experimentais obtidos no Brasil bem como na literatura básica relacionada à nutrição de ruminantes. Diversas associações entre características da forragem pastejada, a composição dos suplementos e os requerimentos microbianos e dos animais foram estabelecidas. A abordagem adotada foi organizada de acordo com duas diferentes estações climáticas observadas em regiões tropicais: estação seca e estação chuvosa. Durante a estação seca as principais limitações nutricionais estão associadas a deficiências relacionadas aos requerimentos dos microrganismos fibrolíticos do rúmen. Deficiência global de compostos nitrogenados é verificada na forragem, o que compromete o consumo e a digestão da forragem. A suplementação com compostos nitrogenados deve ser prioritária nesta estação para se incrementar o consumo de forragem e a extração de energia a partir da fibra. Contudo, durante a estação chuvosa não são observadas limitações inerentes ao crescimento microbiano. A composição da forragem revela, em media, uma elevada relação energia:proteína em comparação à mesma relação nos requerimentos dos animais. Nestes casos, a suplementação proteica se faz necessária para equilibrar a dieta basal e melhorar a utilização da energia metabolizável e da proteína metabolizável. Palavras-chave: Forragens tropicais, metabolismo ruminal, produção bovina, suplementação

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“…These authors stated that, over a wide range of portal NH 3 concentrations, the liver is able to extract about 82% of portal NH 3 resulting in a hepatic removal that is, on average, very slightly higher (4%) than portal absorption. In this situation, arterial NH 3 concentrations are maintained constant even when portal NH 3 absorption varies threefold (Parker et al, 1995). This demonstrates the ability of NH 3 detoxification in ruminants under feeding conditions.…”

Section: Discussionmentioning

confidence: 70%

“…In studies on trans-hepatic veno-arterial differences across a range of BW and diet types (high forage or high concentrate), correlations between N intake and liver production of urea N varied between 0.57 (for sheep) and 0.98 (for beef and dairy cattle; Huntington and Archibeque, 1999;Lapierre and Lobley, 2001). Under normal feeding situations, Parker et al (1995) reported that ammonia (NH 3 ) absorbed into the portal vein is efficiently extracted by the liver and detoxified by conversion to urea or glutamine. These authors stated that, over a wide range of portal NH 3 concentrations, the liver is able to extract about 82% of portal NH 3 resulting in a hepatic removal that is, on average, very slightly higher (4%) than portal absorption.…”

Section: Discussionmentioning

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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Metabolic implications of ammonia production in the ruminant

Cited by 92 publications

References 68 publications

Strategies for optimizing nitrogen use by ruminants

Strategies for optimizing nitrogen use by ruminants

Nutritional aspects applied to grazing cattle in the tropics: a review based on Brazilian results

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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