A longitudinal study of energy and nitrogen excretion by fasted cockerels

An experiment was conducted in which the energy and nitrogen voided by cockerels during the final 48 hr of each of 14 72-hr fasts, 28 days apart, were measured. There were 12 Single Comb White Leghorn cockerels of each of two strains aged 150 days at the time of the first excreta collection and 12 birds from each of two meat-type strains aged 268 days at the first collection. Birds that died during the experiment were replaced by similar birds maintained under comparable conditions. Both excreta energy (FE + UE) and excreta nitrogen (FN + UN) varied among time periods and among birds and appeared to be related to metabolic body size. Similar patterns were observed when the FE + UE data were corrected to zero nitrogen balance (FEn + UEn ). There was a significant (P less than .01) quadratic relationship between ambient temperature and FE + UE, FN + UN, and FEn + UEn with higher excreta outputs being associated with either low or high temperatures. Frequently, but not inevitably, higher FE + UE and FN + UN were observed prior to death. The FE + UE was significantly (P less than .01) correlated with FN + UN. In general, the estimated regression coefficient relating energy to nitrogen output was similar to the value, based upon the energy content of chicken urine, used to correct FE + UE to FEn + UEn . However, the analyses indicated that the correction factor may vary among birds or over time and may be related to metabolic body weight. To what extent this variability can be defined and incorporated into metabolic energy assays requires further investigation.