This study evaluated the influence of incubation conditions on the developmental and physiological status of birds in the perinatal period, which spans the end of incubation until the early posthatch period. Embryos were incubated at a normal (37.8°C) or high (38.9°C) eggshell temperature (EST) and a low (17%), normal (21%), or high (25%) O(2) concentration from d 7 until 19 of incubation. After d 19 of incubation, EST was maintained, but O(2) concentrations were 21% for all embryos. Body and organ weights, and hepatic glycogen levels were measured at d 18 of incubation and at 12 and 48 h after emergence from the eggshell. In addition, blood metabolites were measured at 12 and 48 h after emergence from the eggshell. Embryos incubated at a high EST and low O(2) concentration had the highest mortality in the last week of incubation, which may be related to their low yolk-free body mass (YFBM) or a reduced nutrient availability for hatching (i.e., hepatic glycogen). High EST, compared with normal EST, decreased YFBM. This may be due to the shorter incubation duration of 8 h, the lower weight of supply organs (i.e., heart and lung), or a lack of glucose precursors. Because of this lack of glucose precursors, embryos incubated at high EST may have used proteins for energy production instead of for body development at the end of incubation. The YFBM at d 18 of incubation increased with an increase in O(2) concentration. However, differences between the normal and high O(2) concentration disappeared at 12 and 48 h after emergence, possibly because the high O(2) concentration had difficulties adapting to lower O(2) concentrations in the perinatal period. Blood metabolites and hepatic glycogen were comparable among O(2) concentrations, indicating that the physiological status at hatch may be related to the environment that the embryo experienced during the hatching process. In conclusion, EST and O(2) concentration differentially influence the developmental and physiological status of broilers during the perinatal period.

Environmental conditions during incubation such as temperature and O(2) concentration affect embryo development that may be associated with modifications in nutrient partitioning. Additionally, prenatal conditions can affect postnatal nutrient utilization. Using broiler chicken embryos, we studied the effects of eggshell temperature (EST; 37.8 or 38.9 degrees C) and O(2) (17, 21, or 25%) applied from d 7 until 19 of incubation in a 2 x 3 factorial design. Effects of these factors on embryonic survival, development, and nutrient utilization were assessed in the pre- and posthatch period. High EST reduced yolk-free body mass compared with normal EST (36.1 vs. 37.7 g), possibly through reduced incubation duration (479 vs. 487 h) and lower efficiency of protein utilization for growth (83.6 vs. 86.8%). Increasing O(2) increased yolk-free body mass (from 35.7 to 38.3 g) at 12 h after emergence from the eggshell, but differences were larger between the low and normal O(2) than between the normal and high O(2). This might be due to the lower efficiency of nutrient utilization for growth at low O(2). However, the effects of O(2) that were found at 12 h were less pronounced at 48 h posthatch. When O(2) was shifted to 21% for all treatments at d 19 of incubation, embryos incubated at low O(2) used nutrients more efficiently than those incubated at normal or high O(2). An additional negative effect on survival and chick development occurred when embryos were exposed to a combination of high EST and low O(2). Possible explanations include reduced nutrient availability for hatching, decreased body development to fulfill the energy-demanding hatching process, and higher incidence of malpositions. In conclusion, EST and O(2) during incubation affect nutrient utilization for growth, which may explain differences in survival and development. Embryos raised under suboptimal environmental conditions in the prenatal period may develop adaptive mechanisms that still continue in the posthatch period.

Breeder age and broiler strain can influence the availability of nutrients and oxygen, particularly through differences in yolk size and shell conductance. We hypothesized that these egg characteristics might affect embryonic responses to changes in eggshell temperature (EST). This study aimed to investigate the effect of breeder age, broiler strain, and EST on development and physiological status of embryos. A study was designed as a 2 × 2 × 2 factorial arrangement using 4 batches of 1,116 hatching eggs of 2 flock ages at 29 to 30 wk (young) and 54 to 55 wk (old) of Ross 308 and Cobb 500. EST of 37.8 (normal) or 38.9°C (high) was applied from incubation d 7 (E7) until hatching. The results showed that breeder age rather than broiler strain had an influence on yolk size (P = 0.043). The shell conductance was higher in Ross 308 than in Cobb 500 (P < 0.001). A high EST resulted in a higher yolk free body mass (YFBM) compared to the normal EST at E14 and E16, but at 3 h after hatch YFBM was lower when eggs were incubated at high EST compared to normal EST (all P < 0.001). Cobb 500 eggs yielded embryos with a lower YFBM at E14, E18, and 3 h after hatch (all P < 0.05) than Ross 308 eggs. Breeder age had no effect on YFBM, but the RSY weight was higher in embryos from the old flock compared to the young flock embryos at E14 and E16 (both P < 0.05). A 3-way interaction among breeder age, strain, and EST was found, especially for incubation duration, navel quality, and relative heart and stomach weights at 3 h after hatch (all P < 0.05). Based on the results obtained, we conclude that oxygen availability rather than nutrient availability determines embryonic development, and the egg characteristics affected embryonic responses to changes of EST, especially for variables related to chick quality.

Effects of long-term climatic stress (heat exposure), short-term hygienic stress [lipopolysaccharide (LPS)], or a combination of both challenges on performance of 4 layer lines were investigated. The lines were earlier characterized by natural humoral immune competence and survival rate. At 22 wk of age, 80 hens per line were randomly divided over 2 identical climate chambers and exposed to a constant high temperature (32 degrees C) or a control temperature (21 degrees C) for 23 d. Half of the hens housed in each chamber were i.v. injected with LPS at d 1 after the start of the heat stress period. The effect of heat, LPS, or a combined challenge on feed intake, BW, hen-day egg production, egg weight, and egg shell thickness were investigated. Feed intake, BW, hen-day egg production, egg weight, and egg shell thickness were significantly reduced by heat stress. Administration of LPS significantly reduced feed intake, BW (LPS x time interaction), hen-day egg production, and egg weight (LPS x time interaction). Hens were able to recover from LPS administration but did not completely adapt to heat stress. Hens still lost weight, had a lower feed intake and hen-day egg production after 23 d of continuous exposure to heat stress. These data suggest a different nature of short-term LPS exposure versus long-term heat exposure affecting performance parameters of laying hens, and different adaptation mechanisms of hens toward these stressors. Neither natural humoral immune competence nor survival rate, for which the lines had been earlier characterized, were indicative of the response to different stressors. However, significant line x heat interactions were found for feed intake and hen-day egg production, and a line x heat x time interaction for BW, whereas a line x LPS interaction was found for hen-day egg production and a line x LPS x time interaction for BW. The lines had similar response patterns, but differed in response levels, suggesting that some lines were better able to adapt to stressors than others.

Leg problems in broiler chickens may partly be prevented by providing optimal circumstances for skeletal development during incubation. One of the factors demonstrated to affect bone development is eggshell temperature (EST), which provides a reliable reflection of embryo temperature. The present experiment aimed to investigate the effect of EST on development and asymmetry of the femur, tibia, and metatarsus in broiler chicken hatchlings. Eggs were incubated from d 0 until hatch at 1 of 4 EST: low (36.9°C), normal (37.8°C), high (38.6°C), and very high (39.4°C). At hatch, chick quality was determined in terms of chick length, yolk-free body mass, navel score, and organ weights. Tibia, femur, and metatarsus were weighed, their length and width (mediolateral diameter) and depth (craniocaudal diameter) at the middle of the shaft were measured, and their ash content was determined. Relative asymmetry of the leg bones was determined from their relative dimensions. Hatchability, chick quality, and organ development were lower for very high EST compared with all other treatments. Very high EST resulted in lowest tibia and metatarsus lengths (-3.1 to -8.4%) compared with all other treatments, and lower metatarsus weight (-9.1%) and femur length (-4.9%) compared with high EST. Relative asymmetry and ash content did not differ among treatments and no relation between EST and bone parameters was found. To conclude, very high EST resulted in lower bone development, hatchability, and chick quality. Few differences in bone development and chick quality were found between low, normal, and high EST.