title: Using blood urea nitrogen to predict nitrogen excretion and efficiency of nitrogen utilization in cattle, sheep, goats, horses, pigs, and rats.
abstract: The objectives of this study were to evaluate the potential for using blood urea N concentration to predict urinary N excretion rate, and to develop a mathematical model to estimate important variables of N utilization for several different species of farm animals and for rats. Treatment means (n = 251) from 41 research publications were used to develop mathematical relationships. There was a strong linear relationship between blood urea N concentration (mg/100 mL) and rate of N excretion (g x d(-1) x kg BW(-1)) for all animal species investigated. The N clearance rate of the kidney (L of blood cleared of urea x d(-1) x kg BW(-1)) was greater for pigs and rats than for herbivores (cattle, sheep, goats, horses). A model was developed to estimate parameters of N utilization. Driving variables for the model included blood urea N concentration (mg/100 mL), BW (kg), milk production rate (kg/d), and ADG (kg/d), and response variables included urinary N excretion rate (g/d), fecal N excretion rate (g/d), rate of N intake (g/d), and N utilization efficiency (N in milk and gain per unit of N intake). Prediction errors varied widely depending on the variable and species of animal, with most of the variation attributed to study differences. Blood urea N concentration (mg/100 mL) can be used to predict relative differences in urinary N excretion rate (g/d) for animals of a similar type and stage of production within a study, but is less reliable across animal types or studies. Blood urea N concentration (mg/100 mL) can be further integrated with estimates of N digestibility (g/g) and N retention (g/d) to predict fecal N (g/d), N intake (g/d), and N utilization efficiency (grams of N in milk and meat per gram of N intake). Target values of blood urea N concentration (mg/100 mL) can be backcalculated from required dietary N (g/d) and expected protein digestibility. Blood urea N can be used in various animal species to quantify N utilization and excretion rates.
authors.affiliation: Department of Animal and Avian Sciences, University of Maryland, College Park 20742, USA. rkohn@umd.edu <rkohn@umd.edu>
authors.forename: R A
authors.initials: RA
authors.lastname: Kohn
authors.forename: M M
authors.initials: MM
authors.lastname: Dinneen
authors.forename: E
authors.initials: E
authors.lastname: Russek-Cohen
mesh_terms: D000818:Animals; D000829:Animals, Domestic / Q000502:physiology*; D001806:Blood Urea Nitrogen; D002417:Cattle; D004044:Dietary Proteins / Q000378:metabolism*; D004063:Digestion / Q000502:physiology; D006041:Goats; D006736:Horses; D008322:Mammals / Q000502:physiology*; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism* / Q000493:pharmacokinetics / Q000652:urine; D051381:Rats; D012044:Regression Analysis; D012756:Sheep; D013552:Swine; D013997:Time Factors
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen