In a commercial hatchery, chicks (or poults) hatch over a 24-48 hour period. All chicks remain in the incubator until the majority of the chicks have emerged from the shell. Once removed from the incubator, the newly hatched chick has to undergo several hatchery treatments and is then transported before being placed on the broiler farm. This means that, under practical conditions, chicks are deprived of feed and water for up to 72 hours. In addition, the time of hatch within the hatching window and the spread of hatch cause variability in the amount of time that chicks are feed deprived. Literature on feed deprivation after hatch clearly demonstrates the detrimental effects of any delay in feed access on performance of the chicks with respect to growth, immune system activation, digestive enzyme stimulation and organ development. Improved management strategies, such as shortening the hatching window or the time to first feeding by specific management measures, provide an alternative in dealing with the negative effects caused by a delay in feed access. The development of pre-starter diets that better meet the needs of the newly hatched chicks or in ovo feeding to bridge the gap between hatch and first feeding provide other alternatives in overcoming these problems. However, speculation remains regarding the importance of in ovo or early feeding, or whether the in ovo or early feeding itself is responsible for the beneficial effects reported. The aim of the following review is to discuss the current status of research into early feeding and to stimulate future and further research regarding these topics.

For hatcheries, not only is it important to have a high level of hatchability, but the quality of the chicks provided also has to be good, because broiler farmers are looking for chicks with a high growth potential, resulting in a greater slaughter yield at the end of the rearing period. However, chick quality has proven to be a difficult and subjective matter to define. Therefore, the aim of this study was to investigate the predictive value of different chick quality measurements for BW at slaughter age. Body weight, chick length, shank length, and toe length measurements as well as Tona score determination were performed on 1-d-old chicks and were linked to posthatch performance parameters. Different breeder lines (Cobb and Ross) and breeder ages (39, 42, and 53 wk of age) were used to investigate line and age effects. In addition, variability between people and repeatability in time of these quality measurements were determined. Body weight at 7 d of age appeared to be the best predictor of BW at slaughter age among all the quality measurements performed. Body weight at 1 d of age had the second greatest predictive value, closely followed by the ratio between BW at 1 d of age and chick length squared. Chick length and shank length both had low to no predictive value whatsoever for posthatch performance. The lack of significant correlations between the Tona score and posthatch performance could be explained by the absence of day-old chicks with anomalies (and thus a suboptimal Tona score) because a distinction had already been made, as is done in practice, between top-grade and lower grade chicks.

A multilevel housing system for broilers was developed, named Patio (Vencomatic BV, Eersel, the Netherlands), in which the hatching and brooding phase are combined. In a Patio system, climate conditions differ from those provided in the hatchers currently in use. We compared the physiology of broilers hatched in a hatcher or in a Patio system, and included the effects of hatching time. Eggs from 1 breeder flock were incubated until embryonic d 18 in a setter and subsequently placed in a hatcher or the Patio until the end of incubation. From each hatching system, 154 chicks were collected per hatching time, at 465 h (early), 480 h (midterm), and 493 h (late) of incubation, from which 24 chicks/group were decapitated for analyses of blood plasma and organ weights. The remaining 130 chicks in each group from both systems were individually labeled and placed together in the Patio system. All chicks were given access to feed and water directly after hatch and were housed up to d 45 to monitor growth. From embryonic d 18 until the end of incubation, average ambient temperature and RH were 38.1°C and 50.8% in the hatcher and 35.2°C and 29.7% in the Patio system. Glucose and corticosterone were slightly higher in hatcher chicks, whereas organ weights were not affected by the hatching system. Although hatchling weights were lower in hatchery chicks, growth from d 0 to 45 was not affected by the hatching system. In both systems, glucose increased with hatching time, whereas lactate and triiodothyronine levels decreased. Yolk weights decreased with hatching time, whereas absolute and relative weights of the yolk-free body, intestines, stomach, lungs, and heart increased, indicating more advanced maturation of organs. Growth up to d 21 was depressed in chicks in the late group, which was possibly related to lower thyroid hormone levels at hatching. We conclude that the hatching system had minor effects on hatchling physiology and that posthatch growth and livability were not affected. Because hatching time affected broiler physiology, it seems important to take hatching time into account in future studies related to hatchling physiology.

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Embryonic development is a dynamic process that requires a fine balance between several factors in order to achieve an optimum hatchability and chick quality. These factors include the background of the embryo, such as genetic line of the breeders, the age of the breeder, egg weight, and factors related to the environment in which the egg is stored and incubated, such as temperature, humidity, gas levels and altitude. Gas exchanges are of fundamental importance for embryonic development during incubation and may affect the livability of the embryo. This paper reviews the roles of the gaseous environment (i.e. O 2 and CO 2 ) around hatching eggs during storage and during incubation and the effect it might have on the survival of the developing embryos and the chicks that hatch. The state of the art on the different attempts to establish the optimum requirements of different gases that promote the optimal developmental trajectories at different periods during incubation is presented. The roles and consequences of different levels of O 2 and CO 2 during storage and incubation on hatchability, incubation duration, hatching process, embryo growth, embryo mortality, organ development and morphology, metabolism, blood acid-base balance, chick quality and chick post-hatch growth are reviewed.