In three experiments, Peterson x Hubbard broilers were reared at different stocking densities (SD) in an environmentally controlled (cool cells) house in Yucatan, Mexico. Males were housed until 7 wk of age at: 10, 12, and 14 birds/m² in Experiment 1: 14,15, and 16 birds/m² in Experiment 2; and 17, 17.5, and 18 birds/m² in Experiment 3. For females the SD were 11, 13, and 15 birds/m², 15, 16, and 17 birds/m², and 18, 19 and 20 birds/m². The highest SD of 18 males/m² resulted in only a 3% decrease in 7-wk body weight compared with the lowest density of 10 males/m². For females, the difference between the highest and lowest SD was only 1.5%. The reductions in feed consumption at the highest SD compared with the lowest were 3.7 and 3.9% for males and females, respectively. SD did not affect feed conversion or mortality in any of the experiments. The kg of broiler/m² and profit margins increased with SD up to 17 males/m² and 19 females/m².

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.