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

Area of Science:

• Animal Nutrition and Metabolism
• Digestibility and Nitrogen Balance Studies
• Isotope Tracer Applications in Poultry

Background:

• Accurate measurement of total endogenous nitrogen losses (tENL) is crucial for determining dietary true nitrogen digestibility in broilers.
• Current methods like enzymatically hydrolysed casein (EHC) and EHC-ultrafiltration (EHC-UF) have limitations for diet-specific tENL quantification.
• The 15N-isotope dilution (ID) method offers a potential approach for measuring both basal and diet-specific ENLs.

Purpose of the Study:

• To quantify total endogenous nitrogen losses (tENL) in broilers using a minimally invasive 15N-isotope dilution (ID) method.
• To validate the ID method by comparing its estimates with traditional EHC and EHC-UF methods.
• To assess the utility of urinary 15N-enrichment as a proxy for the precursor pool 15N-enrichment in broilers fed varied diets.

Main Methods:

• A total of 432 female broilers were fed diets varying in fibrous ingredients or a semi-synthetic diet with EHC.
• A 15N-isotope solution (milk protein concentrate and ammonium chloride) was administered orally to broilers from day 26 to 31.
• Excreta, ileal digesta, and tissue samples were collected for nitrogen and 15N-enrichment analysis; urinary 15N-enrichment served as a precursor pool proxy.

Main Results:

• Urinary 15N-enrichment rapidly reached a steady state, correlating well with tissue 15N-enrichment (r=0.84-0.90).
• Ileal tENL estimates from the ID method were significantly lower than those from EHC (-75.6%) and EHC-UF (-70.3%) methods.
• The ID method resulted in slightly lower true ileal nitrogen digestibility estimates (-1 to -4%-units) compared to EHC/EHC-UF.

Conclusions:

• The minimally invasive 15N-isotope dilution method is a viable and practical tool for quantifying total endogenous nitrogen losses in broilers.
• Utilizing urinary 15N-enrichment effectively represents the precursor pool, enabling tENL quantification across diverse dietary fiber and protein sources.
• The ID method provides a valuable alternative for comparing total endogenous nitrogen losses and assessing true ileal nitrogen digestibility in poultry.