Relationship of Feed Efficiency to Carcass Composition and Metabolic Rate in Laying Birds

Abstract

From a population of SCWL laying hens, 100 birds were classified according to their efficiency of conversion of feed to egg mass. From these, 4 “efficient” and 3 “inefficient” birds were used in energy metabolism studies involving indirect calorimetry, while the remainder were used for carcass analysis. Birds maintaining a criteria of 13.5—15.5 kg egg/48 weeks and classified as efficient or inefficient with respect to feed conversion had comparable body weight gains and did not differ significantly (P≤.05) in the protein or fat content of their carcasses. In terms of energy metabolism, efficient and inefficient birds (selected on the basis of similar body size and egg mass production) showed no significant (P≤.05) difference in their ability to metabolize dietary energy. In metabolism chambers, however, inefficient birds produced significantly (P≤.01) more heat under conditions of ad lib. Feeding (.148 vs. .121 kcal/min/kg ) and starvation (.110 vs. .090 kcal/min/kg.75). From a videotaped study of bird activity there was an indication that this difference in metabolic rate was related to bird movement since inefficient birds spent less time resting and more time standing and feeding than did the efficient birds.