The endocrine interface of environmental and egg factors affecting chick quality

Day-old chicks are the endproduct of the hatchery industry and form important starting material for the broiler farms. The major objective is to obtain a high hatchability of marketable chicks and a low spread of hatch. For the farmers, these chicks have to perform well, which is translated in high viability, high growth rate, high breast meat yield, and low feed conversion. A good-quality 1-d-old chick is hence a crucial hinge between the hatchery and the broiler farm. Moreover, maximal hatchability is not always synonymous with maximal posthatch viability and growth potential of the chick. Quantitative and qualitative scoring of chick quality is assessed. We will briefly discuss some recently developed scoring systems, which will convert differences in qualitative parameters into a quantitative score. Preincubation factors such as egg storage duration and age of broiler breeders, as well as incubation conditions, affect day-old chick quality and subsequent broiler performance. Heat production and metabolism, hormonal balances of thyroid hormones and corticosterone, and gas exchange (O(2), CO(2)) are of fundamental importance for embryonic development and survival during incubation. Results from our studies indicated that embryos with higher pCO(2) levels in the air cell and higher triiodothyronine-thyroxine ratios at internal pipping or in the newly hatched chicks had higher hatchability, chick quality, and posthatch chick growth until 7 d of age. Incubation factors such as temperature, turning conditions, or gaseous environment also affect development, change concentrations of hormones related to metabolism and growth of the embryo, and in this way affect 1-d-old chick quality. Moreover, the spread of the hatch process is affected by incubation conditions as well as by the aforementioned preincubation factors. Depending on the spread of the hatching curve together with the place in the sequence of hatching (early or late) and in interaction with quality of the eggs set for incubation, storage duration, and age of breeders, there will be a period between hatch and first feeding of variable length. This may have repercussions on overall growth and many related physiological processes such as yolk uptake, metabolic level, and gastrointestinal development. In its turn, time of first feeding is related to some crucial hormone levels and enzyme activities for growth that are strongly influenced by posthatch food intake such as insulin and p70S6 kinase activity, a key enzyme in the control of protein synthesis. The magnitude of the effect of delayed feeding is dependent on the spread of hatching as well as on the hatching period within the hatching window. This may be related to the different intrinsic quality or characteristics of chicks, e.g., early vs. late hatchers, as is shown by their respective hormonal levels. The latter may be a causal factor for the actual hatching time within the hatching window as well as for the later intrinsic quality of the hatched chick, which is not reflected in any of the actual scoring systems for chick quality. This is largely ignored in previous studies and in hatchery practice so far.