[Energy metabolism in laying hens of different body weight genotypes]

Energy metabolism and some performance parameters were investigated in laying hens of 3 different body weight-genotypes: 6 x 7 (normal-sized, crossbred from normal-sized male and female lines, group 1), 47 x 38 (dwarf-sized, breeding from a dwarf-sized male line and a normal-sized female line, group 2) and 44 x 47 (dwarf-sized, breeding from dwarf-sized male and female lines, group 3). Energy balance was measured by indirect calorimetry through C- and N-balances in 12 animals of each group during 10 consecutive days at production peak, within the period between the 27th and the 37th week of age. Hens were caged individually at 23 degrees C environmental temperature and fed ad libitum on a laying mash. The mean body weight in the dwarf-sized groups 2 and 3 was 32% lower than in the normal-sized group 1 during the energy balance period. The daily gross energy intake in group 2 and 3 was decreased by 33 and 34%, respectively. There were no significant differences in digestibility and metabolizability of gross energy between the groups. The energy requirements for maintenance [kJ ME/kg0.75.d] derived from the energy balances were lower by 4% (P > 0.05) and 14% (P < 0.05) in the dwarf-sized groups 2 and 3 as compared with the normal-sized group 1, when equal coefficients of partial efficiency of metabolizable energy utilization for energy retention in body and eggs are assumed for the 3 body-mass genotypes. There were no relevant differences in body composition at the end of the energy balance periods as well as in egg composition between the 3 experimental groups.