Quantitative aspects of blood and amino acid flows in cattle

Lescoat, Philippe; Sauvant, Daniel; Danfær, A.

doi:10.1051/rnd:19960202

Cited by 26 publications

(24 citation statements)

References 55 publications

(57 reference statements)

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“…Mammary blood flow (MBF, l/day (16)) was predicted from RMY using the following equation obtained by a reevaluation of the model proposed by Lescoat et al (1996) MBF ¼ 3048 þ 414 RMY:…”

Section: Methodsmentioning

confidence: 99%

Dynamic model of the lactating dairy cow metabolism

Martin

Sauvant

2007

Animal

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The whole-animal model described in this paper is intended to be a research model with an intermediary structure between sophisticated and simple cow models. The mechanistic model structure integrates the main metabolic pathways of the lactating dairy cow. Milk yield and related feed intake for varying production potentials were considered to be the driving forces and were empirically defined. The model was designed to explain the main metabolic flows and variations in body reserves associated with the push of nutrients from dry matter intake and their pull by the mammary gland to synthesise milk components throughout lactation. The digestive part of the model uses either known feed unit systems (e.g. PDI system for protein) or published empirical equations for the prediction of digestive flows of organic matter, starch and fatty acids and ruminal volatile fatty acid production. The metabolic sub-system is made up of four tissue compartments (body protein, body lipid, protein in the uterus and triglycerides in the liver) and five circulating metabolites (glucose, amino acids, acetate 1 butyrate, propionate, and triglycerides and non-esterified fatty acids). A major original aspect of the model is its homeorhetic control system. It was assumed that flows relating to adipose and protein tissue anabolism and catabolism were driven by a couple of linked theoretical hormones controlling mobilisation and anabolism. The evolution in body composition and body weight were outcomes of this control. Another originality of the model is its suitability for milk yields varying from 10 to 50 kg at peak production. This was achieved by homeorhetic control of milk potential acting on several key metabolic flows. Homeostatic regulation was also introduced in order to confine the behaviour of the model within realistic physiological values. For some basic aspects (e.g. Uterine involution, standard kinetics of body protein and fat), it was necessary to build specific databases from the literature and interpret these by meta-analysis. Fairly realistic simulated kinetics were obtained for body composition, liver triglycerides, blood plasma metabolite concentrations, milk protein and fat contents, and also for major groups of milk fatty acids.

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“…Mammary blood flow (MBF, l/day (16)) was predicted from RMY using the following equation obtained by a reevaluation of the model proposed by Lescoat et al (1996) MBF ¼ 3048 þ 414 RMY:…”

Section: Methodsmentioning

confidence: 99%

Dynamic model of the lactating dairy cow metabolism

Martin

Sauvant

2007

Animal

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“…Infusing a nitric oxide donor in the external pudic artery increased mammary blood flow in lactating goats, but not milk yield (Lacasse and Prosser, 2003). Thus, mammary blood flow is apparently also subjected to other systemic control mechanisms and is affected by milk yield (Lescoat et al, 1996) and long-term administration of recombinant bovine somatropin, which increases mammary blood flow by 20% to 30% (Chaiyabutr et al, 2005). Mackle et al (2000) and Bequette et al (2001) observed a 40% and 50% increase in mammary blood flow during a 4-day hyperinsulinemic-euglycemic clamp in dairy cows and goats, respectively.…”

Section: Factors Affecting the Efficiency Of N Utilization In The Mammentioning

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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“…Efforts to relate anabolic response to blood flow or arterial concentration, i.e., AA supply, have proved unsuccessful (Lescoat et al 1996). Indeed, supply via the blood is greatly in excess of net gain by both the mammary gland (Bequette et al1996a,b) and muscle (Biolo et al 1992) (Fig.…”

Section: Peripheral Tissuesmentioning

confidence: 99%

Protein turnover—what does it mean for animal production?

Lobley¹

2003

Can. J. Anim. Sci.

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Lobley, G. E. 2003. Protein turnover-what does it mean for animal production? Can. J. Anim. Sci. 83: 327-340. The dynamics of protein turnover confer great advantages for homeothermy, plasticity and metabolic function in mammals. The different roles played by the various organs have led to aspects of protein synthesis and degradation that aid the various functions performed. The so-called "non-productive" organs such as the gastro-intestinal tract and liver produce large quantities of export proteins that perform vital functions. Not all these proteins are recovered, however, and thus function can result in lowered net conversion of plant protein to animal products. The splanchnic tissues also oxidize essential amino acids (AA). For example, the gut catabolizes leucine, lysine and methionine, but not threonine and phenylalanine, as part of a complex interaction between AA supply and tissue metabolic activity. Losses by oxidation and endogenous secretions can markedly alter the pattern of absorbed AA. The fractional rates of extraction of total AA inflow to the liver are low and this allows short-term flexibility in controlling supply to peripheral tissues. Recent evidence suggests that the role of the liver in AA catabolism is more a response to non-use by other tissues rather than an immediate regulation of supply to the periphery. Neither arterial supply of AA nor the rate of transport into peripheral tissues limits protein gain, except when supply is very limited. Rather, control is probably exerted via hormone-nutrient interactions.Key words: Protein synthesis, amino acid, gastro-intestinal tract, liver, muscle, mammary gland Lobley, G. E. 2003. Le taux de renouvellement des protéines-quelle est sa signification en production animale ? Can. J. Anim. Sci. 83: 327-340. La dynamique reliée au renouvellement des protéines confère une grande flexibilité aux mammifères pour maintenir leur homéothermie et leurs fonctions métaboliques. Les divers rôles joués par les organes les ont conduit à des niveaux différents de la synthèse et de la dégradation protéique en fonction des rôles métaboliques à accomplir. Les organes communément appelés « non-productifs » tels le système gastro-intestinal et le foie produisent des quantités importantes de protéines exportées qui accomplissent des fonctions vitales. Cependant, la récupération des ces protéines n'est pas complète et ces fonctions peuvent ainsi résulter en une diminution de la conversion nette des protéines végétales en produits animaux. De plus, le tissu splanchnique oxyde aussi les acides aminés (AA) essentiels. Par exemple, le système digestif catabolise la leucine, la lysine et la méthionine, mais non pas la thréonine et la phénylalanine. Les pertes causées par l'oxydation et les sécrétions endogènes peuvent profondément altérer le profil des AA absorbés. Le taux d'extraction hépatique du flux afférent des AA totaux est faible et ceci permet une flexibilité à court-terme pour contrôler l'apport aux tissus périphériques. Des évidence récentes suggèrent que le rôle ...

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Quantitative aspects of blood and amino acid flows in cattle

Cited by 26 publications

References 55 publications

Dynamic model of the lactating dairy cow metabolism

Dynamic model of the lactating dairy cow metabolism

Strategies for optimizing nitrogen use by ruminants

Protein turnover—what does it mean for animal production?

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