Investigating the eggshell conductance and embryonic metabolism of modern and unselected domestic avian genetic strains at two flock ages

The objective of this study was to determine if broiler strain and breeder flock age affect eggshell conductance, fertility, and hatchability parameters; heart and hepatic glycogen concentrations at hatch; and embryonic metabolism throughout incubation. The 3 broiler strains investigated were HBY, a modern commercial broiler strain selected for high breast yield; WBM, a modern commercial broiler strain selected for the whole bird market; and UN78, a female broiler parent strain unselected since 1978. Fertility and hatchability parameters for each of the 3 strains were determined when the flocks were 32, 34, 37, and 38 wk of age. Eggshell conductance was measured on separate eggs produced from flocks at 37, 45, and 53 wk of age. Concurrently, fertile hatching eggs from the 3 broiler strains at 2 flock ages (33 and 38 wk) were incubated in individual metabolic chambers. Total daily CO2 production of each embryo was measured. Strain and flock age did not influence any of the fertility or hatchability parameters. Strain had no effect on conductance, but eggs from the 37-wk-old flocks had higher conductance than eggs from the 45- or 53-wk-old flocks, which did not differ from one another. Strain had no significant effect on average total CO2 production over the entire 21.5 d of incubation. However, embryos from the 38-wk-old flock produced more total CO2 than did embryos from the 33-wk-old flocks. Also, there was an interaction between strain and flock age for total CO2 production; UN78 embryos from the 33-wk flocks had higher CO2 production than WBM embryos, and the CO2 production of HBY did not differ from either strain. When embryos from the 38-wk flocks were compared, WBM embryos had higher CO2 production than did UN78 embryos, and HBY embryos did not differ from either strain. The data showed that in the 3 strains examined in this study, genetic differences in embryonic metabolic rate were dependent upon breeder flock age.