title: Diet-animal fractionation of nitrogen stable isotopes reflects the efficiency of nitrogen assimilation in ruminants.
abstract: The natural abundance of ¹⁵N in animal proteins (δ¹⁵Nanimal) is greater than that in the diet consumed by the animals (δ¹⁵Ndiet), with a discrimination factor (Δ¹⁵N = δ¹⁵Nanimal - δ¹⁵Ndiet) that is known to vary according to nutritional conditions. The objectives of the present study were to test the hypothesis that Δ¹⁵N variations depend on the efficiency of nitrogen utilisation (ENU) in growing beef cattle, and to identify some of the physiological mechanisms responsible for this N isotopic fractionation in ruminants. Thus, we performed the regression of the Δ¹⁵N of plasma proteins obtained from thirty-five finishing beef cattle fed standard and non-conventional diets against different feed efficiency indices, including ENU. We also performed the regression of the Δ¹⁵N of different ruminant N pools (plasma and milk proteins, urine and faeces) against different splanchnic N fluxes obtained from multi-catheterised lactating dairy cows. The Δ¹⁵N of plasma proteins was negatively correlated with feed efficiency indices in beef cattle, especially ENU (body protein gain/N intake) and efficiency of metabolisable protein (MP) utilisation (body protein gain/MP intake). Although Δ¹⁵N obtained from different N pools in dairy cows were all negatively correlated with ENU, the highest correlation was found when Δ¹⁵N was calculated from plasma proteins. Δ¹⁵N showed no correlation with urea-N recycling or rumen NH₃ absorption, but exhibited a strong correlation with liver urea synthesis and splanchnic amino acid metabolism, which points to a dominant role of splanchnic tissues in the present N isotopic fractionation study.
authors.affiliation: Institut National de la Recherche Agronomique, UMR 1213 INRA-VetAgroSup, Unité Mixte de Recherches sur les Herbivores,63122St Genès Champanelle,France.
authors.forename: G
authors.initials: G
authors.lastname: Cantalapiedra-Hijar
authors.affiliation: Institut National de la Recherche Agronomique, UMR 1213 INRA-VetAgroSup, Unité Mixte de Recherches sur les Herbivores,63122St Genès Champanelle,France.
authors.forename: I
authors.initials: I
authors.lastname: Ortigues-Marty
authors.affiliation: Institut National de la Recherche Agronomique, UMR 1213 INRA-VetAgroSup, Unité Mixte de Recherches sur les Herbivores,63122St Genès Champanelle,France.
authors.forename: B
authors.initials: B
authors.lastname: Sepchat
authors.affiliation: Institut National de la Recherche Agronomique, UMR 1213 INRA-VetAgroSup, Unité Mixte de Recherches sur les Herbivores,63122St Genès Champanelle,France.
authors.forename: J
authors.initials: J
authors.lastname: Agabriel
authors.affiliation: Institut National de la Recherche Agronomique, CRNH-IdF, UMR914 Unité Physiologie de la Nutrition et du Comportement Alimentaire,Paris,France.
authors.forename: J F
authors.initials: JF
authors.lastname: Huneau
authors.affiliation: Institut National de la Recherche Agronomique, CRNH-IdF, UMR914 Unité Physiologie de la Nutrition et du Comportement Alimentaire,Paris,France.
authors.forename: H
authors.initials: H
authors.lastname: Fouillet
mesh_terms: D000818:Animals; D017849:Animals, Inbred Strains; D015415:Biomarkers / Q000032:analysis / Q000097:blood / Q000378:metabolism / Q000652:urine; D001798:Blood Proteins / Q000032:analysis / Q000096:biosynthesis; D002417:Cattle; D003612:Dairying; D004044:Dietary Proteins / Q000378:metabolism*; D005260:Female; D005602:France; D007774:Lactation / Q000097:blood / Q000378:metabolism; D008297:Male; D039382:Maternal Nutritional Physiological Phenomena; D008460:Meat / Q000032:analysis; D008894:Milk Proteins / Q000096:biosynthesis*; D008954:Models, Biological; D009124:Muscle Proteins / Q000096:biosynthesis*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes; D012820:Silage; D013152:Splanchnic Circulation; D014886:Weaning
chemical_list: D015415:Biomarkers; D001798:Blood Proteins; D004044:Dietary Proteins; D008894:Milk Proteins; D009124:Muscle Proteins; D009587:Nitrogen Isotopes
keywords: Ruminants