The Energy Content of Fat and Protein in Chicks and Adult Cockerels

Data were obtained from analyses of the carcasses of four lots of birds: 1) 25♂ + 29♀ broiler chicks 18 days of age; 2) 40♂ + 79♀ broiler chicks 22 days of age; 3) 36♂ adult Single Comb White Leghorn (SCWL) of two strains; and 4) 95♂ adult SCWL of two strains. Energy (E) values for crude fat (CF) and crude protein (CP) in each lot were estimated by multiple linear regression and principal components analyses. There were no sex differences (P>.05) within Lots 1 and 2 and the estimates based on the two lots were not different. Pooled chick values were 37.45 ± .73 and 24.48 ± .47 MJ/kg for CF and CP, respectively. There were no strain differences within Lot 3 (P>.05), but a strain difference was observed in Lot 4 (P<.01) even after removal of outliers. There was no biological explanation for the difference and pooled estimates of 35.32 ± .36 and 25.37 ± .22 MJ/kg were obtained for CF and CP, respectively. The E of CF differed (P<.01) between chicks and adults but the E of CP did not. In all data sets, the estimates based upon principal component analysis were very similar to those from the multiple regression analysis.