The effects of temperature during late incubation on first week broiler chicken development.

Little is known about applying various eggshell temperatures (EST) during the last week of incubation. In particular, the effect of an EST below 37.8°C during the last week of incubation is poorly investigated. Therefore, we investigated effects of EST of 35.6, 36.7, 37.8, or 38.9°C applied from d of incubation (E) 15, E17, or E19 on hatching pattern, embryonic organ development and first week broiler development and performance. A total of 2,850 first grade eggs of a 43 wk old Ross 308 broiler breeder flock were incubated at an EST of 37.8°C until E15. From E15, E17, or E19 onward, eggs were incubated at an EST of 35.6, 36.7, 37.8, or 38.9°C. Moment of internal pipping (IP), external pipping (EP), and hatch were determined and organ development was measured at E15, E17, E19, IP, EP, and hatch. Chick quality was determined at placement in the broiler house and organ development was measured at d7. BW was determined at placement, d4, and d7. Feed intake (FI) was measured at d4 and d7 and G:F was calculated between placement and d4, and between d4 and d7. A lower EST extended incubation duration compared to a higher EST. The longer incubation duration was mainly caused by the extended time until IP, whereas time between IP and hatch hardly varied between treatments. Relative organ weight was affected by EST. Relative heart weight was affected by EST already from 2 d after start of EST treatment on E15, and effects became more pronounced at longer exposure time to various EST treatments. At hatch, the largest difference in relative heart weight was found between an EST of 35.6 and 38.9°C started at E15 (Δ=64.4%). From E17 onward, EST affected yolk-free body mass (YFBM) and relative stomach weight, where a lower EST resulted in a lower YFBM and relative stomach weight before IP and a higher YFBM and relative stomach weight after IP. From E19 onward, a lower EST resulted in a higher relative liver and spleen weight regardless start time of treatment. Yolk weight and relative intestine weight were not affected by EST before and at E19, but a higher EST resulted in a higher yolk weight and lower relative intestine weight from IP onward. Chick quality at placement was higher at an EST of 35.6°C compared to all other EST treatments, expressed by a longer chick length and highest prevalence of closed navels. BW d7 was higher at an EST of 36.7°C compared to all other EST treatments, which was not caused by a higher FI during the first week. A higher G:F between d0 and d7 was found at an EST of 36.7°C compared to 35.6 and 38.9°C. At d7, a higher relative heart weight was found at an EST of 35.6 compared to 38.9°C. This study indicates that an EST of 38.9°C applied from E15 onward negatively affected chick quality, based on the lower YFBM and lower relative organ growth found at hatch. In addition, an EST of 38.9°C applied from E15 onward negatively affected organ development, and G: F until d7 compared to 37.8°C. Moreover, an EST of 36.7°C had a clear positive effect on embryo development, chick quality, organ development, G:F, and growth performance until d7. An EST of 35.6°C resulted in equal or higher chick quality and organ weights compared to 36.7°C, but this was not reflected in performance parameters. [ABSTRACT FROM AUTHOR]