Quantification of total endogenous nitrogen losses in broilers using a minimally invasive 15N-isotope dilution method

Total endogenous nitrogen ( N ) losses ( ENLs ) measurement in broilers is important for quantifying dietary true N digestibility. Basal ENLs are commonly quantified using enzymatically hydrolysed casein ( EHC ) or EHC-ultrafiltration ( EHC-UF ), whereas diet-specific ENLs require regression methods. Total ( tENL ; basal + diet-specific) ENL can be measured using the 15 N-isotope dilution ( ID ) method. This study aimed to quantify tENL using a minimally invasive ID method based on urinary 15 N-enrichment as a proxy for 15 N-enrichment in the precursor pool for endogenous protein synthesis, and to compare ID-derived tENL with estimates from EHC and EHC-UF methods. A total of 432−day-old female broilers were randomly assigned to 48 pens (nine birds/pen), and fed one of five maize-based diets varying in fibrous ingredients (intact or ground soybean hulls with or without purified arabinoxylans, or ground sugar beet pulp), or a semisynthetic diet containing EHC (molecular weight