Quantitative aspects of protein fractional synthesis rates in ruminants

Protein fractional synthesis rate (FSR) is a key-factor in the characterisation of ruminant metabolism.Published data from the literature were collected and statistically analysed to isolate the factors influencing FSR.FSR varied largely depending on the tissue considered, over a range from 1 to 20.FSR, with the plasma as the precursor pool for protein synthesis, was halved compared to that of the intracellular pool.The method for supplying the amino acid also significantly affects FSR since the flooding dose technique gave higher FSR estimates than the constant infusion technique.The choice of the labelled amino acid infused influenced FSR.There is a ranking order depending on the tissue or organ.The protein and energy levels of the diets significantly increased FSR, which raises the question of the body nitrogen requirements.Moreover, FSR values were dependent on the physiological status of the animals.To conclude, FSR values should be determined simultaneously with other biological parameters in order to obtain a realistic quantitative estimate of the nitrogen turnover rates during intermediary metabolism.protein / fractional synthesis rate / ruminant / methodology / statistical analysis Résumé -Aspects quantitatifs des taux relatifs de synthèse protéique chez le ruminant.Le taux de synthèse protéique (FSR) est un élément clé du métabolisme des ruminants.Les variations de FSR ont été étudiées statistiquement à partir de données de la littérature pour en isoler des facteurs explicatifs.FSR varie dans un rapport de 1 à 20 selon les tissus.Si le compartiment précurseur de la synthèse protéique est le plasma, FSR est divisé par deux comparé à l'hypothèse du compartiment intra- cellulaire comme compartiment précurseur.La technique de surcharge en acides aminés donne des valeurs de FSR supérieures à celles obtenues lors d'une infusion continue.Le choix de l'acide aminé infusé influence aussi significativement FSR de façon variable selon le tissu.La concentration éner- This paper is dedicated to the late Dr Bjorn Eggum * Correspondence and