Chicken Incubation Conditions: Role in Embryo Development, Physiology and Adaptation to the Post-Hatch Environment.

The chicken hatching egg is a self-contained life-supporting system for the developing embryo. However, the post-hatch performance of birds depends on several factors, including the breeder management and age, egg storage conditions and duration before incubation, and the incubation conditions. Studies have determined the effect of incubation factors on chick post-hatch growth potential. Therefore, chick physical quality at hatch is receiving increasing attention. Indeed, although incubation temperature, humidity, turning and ventilation are widely investigated, the effects of several variables such as exposure of the embryo to high or low levels, time of exposure, the amplitude of variations and stage exposures on embryo development and post-hatch performance remain poorly understood. This review paper focuses on chick quality and post-hatch performance as affected by incubation conditions. Also, chick physical quality parameters are discussed in the context of the parameters for determining chick quality and the factors that may affect it. These include incubation factors such as relative humidity, temperature, turning requirements, ventilation, in ovo feeding and delay in feed access. All these factors affect chick embryo physiology and development trajectory and consequently the quality of the hatched chicks and post-hatch performance. The potential application of adapted incubation conditions for improvement of post-hatch performance up to slaughter age is also discussed. It is concluded that incubation conditions affect embryo parameters and consequently post-hatch growth differentially according to exposure time and stage of exposure. Therefore, classical physical conditions are required to improve hatchability, chick quality and post-hatch growth.

Unraveling signatures of chicken genetic diversity and divergent selection in breed-specific patterns of early myogenesis, nitric oxide metabolism and post-hatch growth.

Introduction: Due to long-term domestication, breeding and divergent selection, a vast genetic diversity in poultry currently exists, with various breeds being characterized by unique phenotypic and genetic features. Assuming that differences between chicken breeds divergently selected for economically and culturally important traits manifest as early as possible in development and growth stages, we aimed to explore breed-specific patterns and interrelations of embryo myogenesis, nitric oxide (NO) metabolism and post-hatch growth rate (GR). Methods: These characteristics were explored in eight breeds of different utility types (meat-type, dual purpose, egg-type, game, and fancy) by incubating 70 fertile eggs per breed. To screen the differential expression of seven key myogenesis associated genes (MSTN, GHR, MEF2C, MYOD1, MYOG, MYH1, and MYF5), quantitative real-time PCR was used. Results: We found that myogenesis associated genes expressed in the breast and thigh muscles in a coordinated manner showing breed specificity as a genetic diversity signature among the breeds studied. Notably, coordinated ("accord") expression patterns of MSTN, GHR, and MEFC2 were observed both in the breast and thigh muscles. Also, associated expression vectors were identified for MYOG and MYOD1 in the breast muscles and for MYOG and MYF5 genes in the thigh muscles. Indices of NO oxidation and post-hatch growth were generally concordant with utility types of breeds, with meat-types breeds demonstrating higher NO oxidation levels and greater GR values as compared to egg-type, dual purpose, game and fancy breeds. Discussion: The results of this study suggest that differences in early myogenesis, NO metabolism and post-hatch growth are breed-specific; they appropriately reflect genetic diversity and accurately capture the evolutionary history of divergently selected chicken breeds.

Impact of light stimulation during incubation on hatching traits and post-hatch performance of commercial broilers.

Light in terms of photo- and scoto-periods is the key ambient factor affecting the physiology of birds through establishing normal biological clock and circadian rhythms. In natural incubation light significantly influences embryonic development, however, at commercial setups eggs are incubated under a dark environment. Presently not a single commercial poultry hatchery is using light during incubation; hence, comprehensive studies are needed to address the industry for considering light as a potential embryonic growth stimulant. In the present study, white Light-emitting diodes (LEDs; 5000 K) were installed in the incubator and 250 lx light intensity was provided for 0, 12, and 24 h per day during the whole incubation period. A total of 900 broiler hatching eggs (Hubbard classic; from 58 weeks old parents) were randomly allocated to 3 treatment groups, having 5 replicates of 60 eggs each, a tray was considered as replicate during incubation and these eggs were incubated under standard incubation protocols. After hatching, a total of 300 chicks were picked and divided into 3 described treatments (0, 12, and 24 h of photo-stimulation to eggs during incubation) having 5 replicates of 20 birds each. The results indicated that incubation of eggs under 12 and 24 h of lighting significantly improved (P ≤ 0.05) hatch window, hatchability % (0.0002), a hatch of fertile % (0.001), and carcass yield % (0.0454). Embryonic mortality, dead germs, and dead in shell embryos were lower in eggs incubated under 12 h light. Significantly better FCR (0.0006), stress susceptibilities such as H/L ratio (0.0227), and physical asymmetry (0.0065) were observed among the birds incubated under 12 h light (P ≤ 0.05). In conclusion, an appropriate light stimuli (12 h) may help to improve hatching traits and post-hatch performance of commercial broiler.

In ovo feeding of beta-hydroxy beta-methylbutyrate and dextrin optimized growth performance of broiler for pre-placement holding time using the Box-Behnken response surface design.

To investigate the effect of in ovo feeding (IOF) of beta-hydroxy beta-methylbutyrate (HMB), dextrin and post-hatching water and feed deprivation time on growth performance of broilers, 1,500 eggs were assigned into 15 experimental runs of Box-Behnken design, including three levels IOF of HMB (0%, 0.5% and 1%), dextrin (0%, 20% and 40%) and three levels of the first water and feed deprivation (6, 27 and 48 hr). After hatching, day-old chicks (seven males and seven females) from each replicate were then selected and randomly assigned to 60 floor pens for a 42-day feeding trial. The experimental data were fitted to the quadratic response surface models, and the goodness of fit of the models was expressed by the R2 value. The interaction between IOF of dextrin and timing of first feed deprivation had the largest effect on body weight of chicks at day 7 (BW7) and corrected European production efficiency factor (EPEF). In ovo feeding of dextrin reduced negative effects of delayed access to feed and water after hatch up to 48 hr on BW7, body weight of chicks at day 42, EPEF and corrected EPEF. The results of the current study suggested that the EPEF corrected by hatchability could provide the better understanding of IOF experimental findings. The ridge optimization analysis revealed that the optimal levels of HMB and dextrin inclusion in eggs and timing of first feed deprivation for maximum corrected EPEF were 0.37, 15.94% and 7.22 hr, respectively. These results demonstrate that the Box-Behnken statistical design and response surface models are effective to describe the relationship between IOF of nutrients and pre-placement holding time and predict the performance of broilers to achieve the optimal target.

Egg laying characteristics, egg weight, embryo development, hatching weight and post-hatch growth in relation to oviposition time of broiler breeders.

Two experiments were conducted to determine egg laying characteristics and the effects of oviposition time on egg weight, embryo development and post-hatch growth in broiler breeders. In experiment 1, eggs collected for 3 consecutive days on hourly basis between 06:30 and 17:30h were categorized to early, middle and late oviposition times in the clutch. In experiment 2, eggs were incubated to study embryo development, remaining albumen, liver weight, heart weight and the tibia length of embryos at 12, 14, 16 and 18 days of incubation as well as the body weight of hatchlings and chickens at 7, 21 and 42 days of age in relation to oviposition time. About 76% of nest eggs were laid from 06:30 to 11:30h. A similar pattern was observed in floor eggs. Egg weight decreased (P<0.01) with advanced position in the clutch. Generally, oviposition time had no effect on embryo growth parameters. At hatch, body weight of chicks derived from eggs of late oviposition times was less (P<0.01) than that of chicks from eggs produced earlier in the clutch. From 3-week-old onwards, chickens of early oviposition time sustained heavier (P<0.05) weight than chickens of middle oviposition time whereas chickens of late oviposition time obtained a middle weight. Differences in egg weights, body weight at hatch and post-hatch growth due to time of oviposition suggest that oviposition time together with incubation conditions should be considered for obtaining greater uniformity and growth of chickens.