Data paper: Contribution of lipids to the net carbon balance across the liver and associated measurement uncertainty in dairy cows

Livestock systems are becoming more efficient and require physiological data to better estimate the nutritional requirements of animals. The liver plays a central role in nutrient processing and metabolism. To better understand liver function, five lactating Jersey cows (78 ± 12 days in milk) were surgically fitted with blood catheters in the mesenteric vein (for para-aminohippuric acid ( pAH ) infusion), portal (PV ) and hepatic veins ( HV ), and in the mesenteric artery ( MA ). They were fed four iso-energetic treatment diets [(starch vs fibre-rich diets) × (low vs normal protein diets)] according to a 4 × 4 Latin Square design; each treatment lasted 28 days. The data reported in this study present all the metabolite concentrations (albumin, amino acids, beta-hydroxybutyrate, carbon dioxide, glucose, insulin, lactate, non-esterified fatty acids ( NEFA ), oxygen, phospholipids, total cholesterol, total lipids, total proteins, triglycerides, triiodothyronine, thyroxine, urea and volatile fatty acids) measured in the PV, HV and MA per cow, treatment diet and period. Blood or plasma flow per blood vessel was determined using the Fick principle and the pAH measurements. The afferent (MA and PV) and efferent (HV) fluxes were calculated for most of the carbon-containing metabolites (excluding NEFA, hormones and proteins for which only the concentrations are reported). The net carbon balance across the liver was then calculated as the difference between afferent and efferent fluxes, per cow and treatment diet. Laboratory methods were evaluated by Quality Assurance procedures, which may be used to select the appropriate analytical method for a study. The expanded measurement uncertainty ( MU ) associated with the net carbon balance across the liver was then determined, considering the individual MU of each parameter involved in the calculation. The latter were calculated from statistical distribution of quantity values derived from Quality Assurance procedures (Type A approach; for most of the metabolites) or from other kinds of information when this was not possible (Type B approach; for total lipids, total amino acids and carbon dioxide). The present data may be used to better understand the hepatic metabolism of dairy cows, the MU of nutrient fluxes and the net carbon balance across the liver, and to evaluate the accuracy of existing prediction models. The large expanded measurement uncertainty of the carbon balance values is useful to understand the limits of interpretation of the present net flux data.