. 2021 Jan 6;12:5. doi: 10.1186/s40104-020-00526-2

Table 3.

Methods used for the determination of basal and total endogenous amino acid losses in poultry

Item	Methods
Basal losses	• Fasting of birds for 48 h^a
	• Feeding of a protein-free diet
	• Feeding of diets with very low levels of protein
	• Protein-free diet supplemented with synthetic amino acids
	• Protein-free diets with intravenous amino acid infusion
	• Natural proteins devoid of specific amino acids
	• Enzyme hydrolysed casein^b and ultrafiltration
	• Feeding of highly digestible protein, e.g. wheat gluten, soy protein isolate, casein^b
	• Linear regression, following feeding of diets containing graded levels of specific ingredient
Total losses	• Homoarginine
Total losses	• Isotope-labelled markers

^aSpecific to precision-fed rooster assays [29, 30] and measured in the excreta. Measurement units are function of time (mg/bird/d) rather than intake (mg/kg dry matter intake) and cannot be used as correction factor in other digestibility assays

^bThese proteins are assumed to be (almost) 100% digestible and that excreted amino acids therefore represent endogenous losses