Relationship between body weight and amino acid excretion in fasted mature cockerels

A study was made of the relationship between body weight and the amino acid (AA) excretion of fasted adult Single Comb White Leghorn cockerels. Thirty birds, maintained on a balanced corn-soy diet and individually housed, were weighed and fasted for 30 hr to rid their alimentary canals of feed residues. They were then carried through another 30 hr fast during which metabolic plus endogenous (M + E) excreta were collected and analyzed for the different AA. There was a significant (P less than .05) correlation between body weight of the birds and the excretion levels of most M + E AA. However, the highest correlation coefficient was of the order of about .45. This meant that the maximum variation in the M + E AA excretion associated with changes in body weight was of the order of only 20%. It is concluded from these results that the use of birds of similar body weight as the basis for determining the correction for M + E AA losses in deriving true AA availability (TAAA) values could generate erroneous data. The implications of basing the correction for M + E AA losses upon a small group of randomly selected birds or upon birds of similar body weight to derive TAAA values are discussed.