Rapid growth rate has presented broiler chickens with serious difficulties when called on to thermoregulate efficiently in hot environmental conditions. Altering the incubation temperature may induce an improvement in the acquisition of thermotolerance (AT). This study aimed to elucidate the effect of thermal manipulations (TM) during the development of the thyroid and adrenal axis of broiler embryos on the potential of broilers to withstand acute thermal stress at marketing age. Cobb broiler embryos were subjected to TM at 39.5 degrees C and 65% RH from embryonic day 7 to 16 (inclusive), either continuously (24 h) or intermittently (12 h). After hatching chicks were raised under standard conditions to 35 d of age and then subjected to thermal challenge (35 degrees C for 5 h). Continuous TM caused a significant decline in hatchability, coupled with significantly lower BW and body temperature at hatching. The intermittent (12-h) chicks showed results similar to the controls but had significantly lower body temperature. Thermal challenge at marketing age demonstrated a significant improvement in AT in both the 12- and 24-h TM-treated broilers, which was characterized by a significantly lower level of stress (as evidenced by the level of plasma corticosterone) and rate of mortality. It was concluded that TM during the portion of embryogenesis when the thyroid and adrenal axis develop and mature had a long-lasting effect and improved the AT of broiler chickens. Whereas intermittent TM had no significant effect on hatchability and performance parameters, continuous TM negatively affected these parameters.

The temperature and relative humidity of storage, as well as the gaseous environment, interact with the fertile egg over time during storage in such a way as to affect the success of incubation either negatively or positively. This interaction occurs both above and below the "physiological zero", at which embryonic metabolism is minimal. This interaction below physiological zero implies that certain physical aspects of the egg must be affected by the environmental conditions. As the eggshell is a relatively fixed component, changes in albumen, shell membranes, cuticle, yolk, or embryo proper must account for these time- and environment-related effects. It is concluded that the major contributor is the albumen, as it is obviously the most dynamic component below physiological zero and is strategically positioned.

Three experiments were conducted to investigate the effect of increased egg temperature during the final third of incubation on BW, yolk sac, heart, and digestive organs of broiler chicks at hatching. Egg temperatures were found to be approximately 1.0 to 1.5 degrees C higher than incubator air temperature. Elevated egg temperature (39.5 degrees C) after embryonic day 14 generally accelerated hatching time but decreased the relative weight of the heart in all 3 experiments, whereas BW and relative weights of the gizzard, proventriculus, and small intestines were significantly smaller in 2 of 3 experiments as compared with the control (approximately 38.2 degrees C). Relative weights of the yolk sac or liver were significantly larger due to elevated egg temperature in single experiments only. A striking feature of the chicks that developed at an elevated egg temperature was their white color as compared with the yellow color of chicks from eggs incubated at more normal temperatures.

Broiler hatching eggs from two young (30 and 31 wk) or two old (52 and 53 wk) breeder flocks were stored for 3, 7, or 14 d at 18 C and 75% RH while being turned 0, 4, or 24 times per day in two experiments. Apparent fertility and hatchability of total eggs differed with flock age in both experiments, but the effect was greater in Experiment 1. Hatchability of total and fertile eggs were decreased with flock age in Experiment 1 (31 and 52 wk flocks), but only hatchability of total eggs was decreased in Experiment 2. Hatchability of fertile eggs declined with length of storage period in both experiments with the most obvious effect observed in eggs stored 14 d. There was an increase in percentages of early and late embryonic mortality with length of storage period in both experiments. Hatchability of fertile eggs was increased by turning 4 or 24 times per day during storage in Experiment 1 or by four times per day, with 24 times per day intermediate, in Experiment 2. There were no storage time x turning in storage interactions. A significant interaction of flock age x turning in storage for hatchability of fertile eggs in Experiment 1 suggested that eggs from an older broiler breeder flock that exhibit reduced fertility benefited more from turning during storage than did eggs from a young broiler breeder flock.

Broiler breeder hens were fed diets amended with 0 and 10 mg/kg (Trial 1) or 0, 0.2, 1, or 5 mg/kg (Trial 2) of aflatoxin (AF). Fertile eggs collected during 14 d of AF feeding were examined for AF residues. Various immunological endpoints were examined in chicks hatched from these eggs. Eggs collected at 7 d of AF feeding (Trial 1) had 0.15 to 0.48 ng/g of AFB1 and 0.22 to 0.51 ng/g of aflatoxicol, whereas eggs collected at 14 d of AF feeding had 0.05 to 0.60 ng of AFB1/g and 0.19 to 1.20 ng of aflatoxicol/g. In both trials, AF dietary exposure resulted in embryonic mortality and reduction in hatchability compared to controls. The AF progeny chicks in Trial 2 had total anti-SRBC antibodies similar to the controls during the primary antibody response. However, at 5 and 7 d after secondary SRBC injection, the antibody levels in the 1 and 5 mg/kg AF groups were lower than those of controls. Depression in anti-Brucella abortus antibodies occurred only in chicks from the 5 mg/kg AF group. Furthermore, phagocytosis of SRBC and reactive oxygen intermediate production by macrophages from AF progeny chicks were reduced as compared with the control chicks. The findings of this study imply that the progeny chicks from hens consuming a AF-amended diet may be increasingly susceptible to disease owing to suppression of humoral and cellular immunity.