Protein turnover—what does it mean for animal production?

Abstract

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 ...

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

“…Numerous dietrelated factors can influence N efficiency, such as overfeeding with rumen degradable protein (Hristov et al, 2004), lack of synchronisation between ruminal carbohydrate and protein degradation (Casper et al, 1999), unbalanced composition of amino acids absorbed in the small intestine (Rulquin et al, 1993) and undersupply of -E-mail: nbk@agrsci.dk nutrients other than amino acids (Firkins et al, 2006). However, N efficiency is influenced by not only dietary factors but also the production level of the cow and the inevitable endogenous amino acid catabolism influences overall efficiency (Lobley, 2003). Ruminants have a competitive advantage compared with other species by having a digestive system that makes it possible to reutilise endogenous N. Data reviewed by Lapierre and Lobley (2001) showed that on average 43% of the endogenous urea production was taken up into the gastro-intestinal tract as estimated from the negative net portal flux of urea.…”

Isotope turnover rates and diet-tissue discrimination in skin ofex situBottlenose Dolphins (Tursiops truncatus)

“…Hilderbrand et al, 1996;Zhao and Schell, 2004;Sponheimer et al, 2006). The quality and quantity of protein in a consumer's diet can affect the turnover rate of proteins, thereby altering carbon and nitrogen turnover rates (Lobley, 2003;Zhao et al, 2006). Isotopic turnover rates can also vary among tissue types, species, body sizes and nutritional states Newsome et al, 2010), making comparisons among studies difficult.…”

Food restriction and refeeding in lambs influence muscle antioxidant status

“…The alteration of the growth pattern during compensatory growth is due to significant modifications in both protein synthesis and protein breakdown (Bruce et al, 1991;Van Eenaeme et al, 1998;Hornick et al, 2000). The increase in protein anabolism efficiency during refeeding after food restriction, a highly beneficial adaptation of animals to undernutrition, requires a large amount of energy (Lobley, 2003) and stimulates the mitochondrial redox chain, which is one of the sources of ROS (Aurousseau, 2002;Drö ge, 2002;Griffiths, 2002). Such oxidation processes occurring during these adaptation periods, which happen simultaneously with alterations in the food supply, have not been studied in farm animals.…”