Gas exchange during storage and incubation of Avian eggs: effects on embryogenesis, hatchability, chick quality and post-hatch growth

Carbon monoxide affects early cardiac development in an avian model

INTRODUCTION

Carbon monoxide (CO) is a toxic gas that can be lethal in large doses and may also cause physiological damage in lower doses. Epidemiological studies suggest that CO in lower doses over time may impact on embryo development, in particular cardiac development, however other studies have not observed this association.

METHODS

Here, we exposed chick embryos in ovo to CO at three different concentrations (3, 9, 18 ppm) plus air control (4 protocols in total) for the first 9 days of development, at which point we assessed egg and embryo weight, ankle length, developmental stage, heart weight, ventricular wall thickness, ventricular-septal thickness and atrial wall thickness.

RESULTS

We found that heart weight was reduced for the low and moderate exposures compared to air, that atrial wall and ventricular wall thickness was increased for the moderate and high exposures compared to air and that ventricular septal thickness was increased for low, moderate and high exposures compared to air. Ventricular wall thickness was also significantly positively correlated with absolute CO exposures across all protocols.

CONCLUSIONS

This intervention study thus suggests that CO even at very low levels may have a significant impact on cardiac development.

Influence of non-ventilating intervals during early incubation stage on egg hatching process

Background and Aim

The exchange of oxygen and carbon dioxide (CO2) in the incubator plays a key role in embryonic development and hatching. This study aimed to study the effect of non-ventilated (NV) intervals during the early stage of embryonic development on the hatching process.

Materials and Methods

Hatching eggs (n = 7200) were equally divided into four treatment groups and incubated in four incubators. The first group was incubated in normal ventilated condition (V) during the setting phase of incubation. Ventilation holes of the three remaining incubators were closed for the first 3, 6, and 9 days and termed as NV groups (NV1, NV2, and NV3, respectively). A gradual increase in CO2 was allowed for NV groups, followed by opening the incubator holes to permit ventilation throughout the rest of the incubation periods.

Results

Obtained results demonstrated that CO2 concentration gradually increased up to 0.19% for the NV1 group, 0.41% for the NV2 group, and 0.90% for the NV3 group, while CO2 concentration remained at 0.08% during the first 9 days of incubation in the V group. Albumen pH was lowered for all NV groups. The highest hatchability percentage was recorded for NV3 followed by NV2 and NV1 groups. All NV groups represented earlier and narrower spread of hatch and higher hatched chick weight. Embryos and hatched chicks in the NV groups had higher hormonal levels of thyroxin and corticosterone.

Conclusion

All non-ventilation periods had positive effects on narrowing the spread of hatch, increasing hatched chick weight and hatchability percentage compared to the normal V condition. Furthermore, the non-ventilation throughout the first 9 days of incubation yielded the best hatching results.

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.

Effects of pre-incubation storage duration and nonventilation incubation procedure on embryonic physiology and post-hatch chick performance

This study investigated the effects and possible interactions of storage and nonventilation during incubation for eggs from Sasso broiler breeder flock on pre- and post-hatch incubation results.

A total of 1,260 Sasso eggs from a 58-wk-old broiler breeder flock were individually numbered, weighed and stored for 7 d or for 18 d in a climate-controlled room (16°C, 75% RH). After storage, eggs were weighed, and randomly assigned equally into 2 incubators. One of the incubators was ventilated (V) for the entire incubation and the second was nonventilated (NV) for the first 12 d. At d 18, the eggs were weighed, candled, and fertile eggs were transferred from the turning trays to hatching baskets. During the last 3 d of incubation, hatching eggs were checked individually every 3 h for hatching events and hatchability of fertile eggs. After pull out at d 21.5, post-hatch performances was determined until 1 wk of age.

Results showed that, embryo weights from eggs in NV incubator was significantly higher (P < 0.05) in both stored eggs compared to those from eggs in ventilated incubator, but embryos from eggs stored for 18 d were smaller (P < 0.05) than those from eggs stored for 7 d. Hatchability was higher (P < 0.0001) in NV incubator compared to V incubator in both 7 d and 18 d stored eggs and an interaction was found between incubation ventilation and storage duration on both hatchability and embryonic mortality (P < 0.0001). Chick weights from NV incubator at 7 d post-hatch was greater (P = 0.0009) than those from V incubator. Serum Tri-iodothyronine (T₃) and Thyroxin (T₄) concentrations were significantly higher (P < 0.05) in NV compare to V group.

It was concluded that the effect of long-term pre-incubation storage on embryonic physiology and post-hatch growth interacted significantly with incubation ventilation and that nonventilation can compensate for the negative effects of storage on some hatching and post-hatch performances.

Effects of incubator oxygen and carbon dioxide concentrations on hatchability of fertile eggs, some blood parameters, and histopathological changes of broilers with different parental stock ages in high altitude

The effects of incubator carbon dioxide (CO₂) and oxygen (O₂) concentrations with parental stock age (PSA) on embryonic deaths (ED), hatchability of fertile eggs (HFE), some blood parameters, and the tissue development of broilers were investigated. Four consecutive repetitions following the similar materials and methods were carried. From 3 different aged ROSS 308 broiler parental flocks 7,680 hatching eggs were obtained and classified as young (Y; 29 wk), middle (M; 37 wk) and old (O; 55 wk) as regards PSA, and randomly distributed. Four different incubator ventilation programs (IVP) as control (C; 0.67% CO₂ and 20.33% O₂), high CO₂ (HC; 1.57% CO₂ and 20.26% O₂), high O₂ (HO; 0.50% CO₂ and 21.16% O₂), and high CO₂ + O₂ (HCO; 1.17% CO₂ 21.03% O₂) were applied with oxygen concentrator, and ED and HFE were investigated. Lung and heart tissues, hemoglobin value, packed cell volume, and red blood cell count, triiodothyronine, thyroxine, adrenocorticotropic hormone (ACTH) values of the chicks were analyzed. It was found that IVP affected ED and HFE. Higher rate of early ED (EED) was obtained from the HC than HCO, and higher middle+late stage+pipped but unhatched ED (MLPED) with a lower rate of HFE was observed in the C group than HO and HCO (P < 0.05). Association was found between PSA and IVP (P < 0.05), being more evident in EED for young PSA, in MLPED with HFE for Y and O PSA. From hematological values, no statistical difference in RBC, PCV, and Hb values were found among the treatment groups, ACTH concentration known as a response to stress was found to be higher than C in all groups, triiodothyronine concentration was higher in the HO group than C. In the histopathological examination, used IVPs were found to have negative effects on the lung and heart such as vacuolization, hemorrhage in all PSA groups except for C. Conclusively, PSA and IVP affected some hatching, blood and tissue development parameters of the broiler chicks.

Genetic variations for the eggshell crystal structure revealed by genome-wide association study in chickens

Background

Eggshell is a bio-ceramic material comprising columnar calcite (CaCO₃) crystals and organic proteinaceous matrix. The size, shape and orientation of the CaCO₃ crystals influence the microstructural properties of chicken eggshells. However, the genetic architecture underlying eggshell crystal polymorphism remains to be elucidated.

Results

The integral intensity of the nine major diffraction peaks, total integral intensity and degree of orientation of the crystals were measured followed by a genome-wide association study in 839 F2 hens. The results showed that the total integral intensity was positively correlated with the eggshell strength, eggshell thickness, eggshell weight, mammillary layer thickness and effective layer thickness. The SNP-based heritabilities of total integral intensity and degree of orientation were 0.23 and 0.06, respectively. The 621 SNPs located in the range from 55.6 to 69.1 Mb in GGA1 were significantly associated with TA. PLCZ1, ABCC9, ITPR2, KCNJ8, CACNA1C and IAPP, which are involved in the biological process of regulating cytosolic calcium ion concentration, can be suggested as key genes regulating the total integral intensity.

Conclusions

The findings greatly advance the understanding of the genetic basis underlying the crystal ultrastructure of eggshell quality and thus will have practical significance in breeding programs for improving eggshell quality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08103-1.

Daily oxygen supplementation to the incubator at different stages of embryonic development alters the activity of antioxidant enzymes in the lung tissue of broiler chicks at a high altitude

1. Pulmonary hypertension, associated with mitochondrial function in the lung tissue of broilers, can occur at hypoxic high altitudes. The present research examined the impacts of O₂ supplementation at different embryonic stages on broiler organ development and antioxidant enzyme activities.2. In total, 360 eggs from Ross 308 broiler breeders at sea level were divided into a control group (O₂ non-supplementation group) and three experimental groups daily 1 h 23.5% O₂ supplementation from days 0 to 11 (O_0-11), from days 12 to 21 (O_12-21), and from days 18 to 21 (O_18-21) of embryonic age.3. The lung, heart, right ventricular (RV), and left ventricular (LV) + septum of newly hatched and seven day old chicks from every group were dissected and weighed. Antioxidant enzyme activities were examined in their lung tissue.4. The lung weight did not change in any group. At hatching, the heart weight (g and %) was higher in the O_12-21 and O_18-21 groups than in the O_0-11 and control groups, but the relative heart weight was the highest in the O_18-21 group in comparison with the O_12-21 group.5. Superoxide dismutase (SOD) activity increased in all experimental groups at both ages, but glutathione peroxidase (GPx) activity increased only in seven day old chicks. Catalase (CAT) exhibited high activity in the O_12-21 and O_18-21 groups at hatching. In the seven day old chicks, while the CAT activity did not change in the O_18-21 group, it decreased in the O_0-11 group and increased in the O_12-21 group.6. Glutathione reductase (GR) activity did not change in the O_18-21 group, but GR exhibited low activity in the O_0-11 group and high activity in the O_18-21 group in newly hatched chicks. The GR activity only decreased in the O_18-21 group of seven day old chicks.7. The results indicated that oxygen supplementation to the incubator caused alterations in the antioxidant enzyme activities in the lungs of broiler chicks, and this may have been in response to oxidative stress.

Incubation, hatchery practice and the welfare of layer hens

For modern layers to achieve optimum production performance and welfare state, the entire production process needs to be managed to achieve target bodyweight, body composition and flock uniformity. In addition to genetic improvements, flock health, environment, nutrition and on-farm husbandry practices, incubation and hatchery practices have become a focal point for producing optimum chick quality. Chick quality is a collective term involving chick size and anatomical features, physiology, robustness and liveability over the first week after placement. Chick quality is a key focus for hatcheries as this has been positively correlated with overall flock performance, especially egg production, shell quality, liveability and animal welfare. Recent advances in incubation have focussed on the benefits of all-in–all-out (single-stage) machines. Innovation in incubation systems is completely conducted today by international manufacturers, and is largely driven by the meat chicken industry. Disposal of male layer chicks has increased as a consumer welfare concern, and while investment in research and legislation changes are focussed towards providing or driving new solutions, there are currently no commercial options for industry to deal with this problem before incubation or hatch. Chick transport systems and equipment have also significantly improved in recent years, providing optimum conditions to ensure temperature uniformity and minimal moisture loss during transit before placement, thus optimising chick quality. Together, recent improvements in incubation equipment and hatchery practice can produce commercial layer chicks that are healthy, of high quality, and are then in an optimal physiological state and condition to achieve their genetic potential.

Effect of storage duration on egg quality, embryo mortality and hatchability in FUNAAB-ɑ chickens

Effect of extended storage on egg quality, embryo mortality and hatchability in FUNAAB-ɑ chickens was determined. Hatchable eggs (n = 288; weighing 53.2 ± 4.67 g) collected from a flock of FUNAAB-ɑ layer breeder hens aged 32 weeks were stored in egg tray with broad end up under 16 ± 1.5°C for either 0, 4, 8, 12, 16 or 20 d. Before incubation, eight eggs from each group were evaluated for internal and external quality traits. Remaining eggs were set in an incubator and transferred into hatcher on embryonic day 18. Data collected were subjected to one-way analysis of variance. Egg weight loss (EWL; p < .001), surface area (p < .001), yolk diameter (p < .001), inner and outer blastoderm diameters (p < .05) and dead in germ (DIG; p < .001) increased with storage duration while yolk height (p < .001), yolk index (p < .001), albumen weight (p < .05), albumen height (p < .05), albumen index (p < .01), Haugh's unit (HU; p < .05), fertility (p < .001), hatchability of set (HATCHS; p < .001) and fertile eggs (p < .05) decreased. Weight losses of 0, 1.2, 2.2, 3.4, 4.6 and 6.1% were recorded in egg stored for 0, 4, 8, 12, 16 and 20 days respectively. Eggs stored beyond 8 days exhibited higher DIG and lower HATCHS. Shell percentage in 4 days storage (11.4%) was lower (p < .05) than in 16 days storage (13.4%). Shell thickness was similar in eggs stored for 0 to 12 days, but 8 days storage (0.60 mm) had thinner (p < .01) shell than day 16 (0.71 mm) and day 20 (0.73 mm) storage. Internal quality unit (IQU) was higher (p < .05) in fresh eggs (180.4) than in 12 days (167.8) and 20 days (167.8) stored eggs. Extended storage of FUNAAB-ɑ eggs caused EWL, surface area shrinkage, lowered HU and IQU, loss of yolk and albumen quality, increased blastoderm diameters and DIG, and decreased egg fertility and HATCHS from day 8 forward. Storing FUNAAB-ɑ eggs beyond 8 days reduced quality parameters; therefore, other mitigating factors are recommended when storing beyond 8 days.

Pre-Incubation and its Effect on the Development and Malformations of The Chick Embryo

This study was conducted to evaluate the effect of eggs stored with and without pre-incubation on chick embryos with emphasis on: embryo body, heart weight, malformations, and mortality. For this study, a total of 120 chick embryos were divided into three groups, based on the length of storage before hatching (3, 7 and 10 days). Observations of the weight of chick embryo bodies, chick embryo hearts, and the level of mortality and appearance of malformations were noted. With an increase in days stored, the chick embryo’s weight decreased. The pre-incubation period had a positive effect on the weight of chick embryo, and chick hearts. Malformations, including: hydrocephalus, open body cavity and underdeveloped wings, were observed in all three groups, with the highest proportion seen in the pre-incubated hatching eggs stored for 10 days; this group also displayed the highest level of mortality. Non-pre-incubated eggs showed the most promise with better results in all experimental groups. In conclusion, the research suggests the optimal storage for chick embryos to be 3 days, with lowest levels of mortality, malformations and limited effects on the body and heart weight.

Responses of developmental and physiological traits to manipulated incubation conditions in broiler embryos at hypoxic high altitude

Abstract. The effects of hypoxia at increased altitude levels on the cardio-respiratory development of broiler embryos are distinct in comparison with those at sea level. The aim of the study was to investigate the effects of high incubation temperature (H) and oxygen supplementation (O) during hypoxic high altitude (HA) on developmental and physiological traits of embryos and hatching performance of embryonated hatching eggs in broilers at different embryonic stages. A total of 1280 eggs obtained from broiler breeders laid at sea level were used. Eggshell quality characteristics were measured for 20 eggs. The rest of the 1260 eggs were divided into seven incubation condition (IC) groups (180 eggs per group) including a control group at 37.8 ∘C and 21 % O2; O groups, with daily 1 h 23.5 % O2 supplementation at 37.8 ∘C as O0−11, O12−21, and O18−21; H groups at 38.5 ∘C high incubation temperature at 21 % O2 as H0−11, H12−21, and H18−21 from days 0 to 11, 12 to 21, and 18 to 21 of incubation, respectively. All groups were incubated in three different incubators at hypoxic HA. The effect of IC was determined on eggshell temperature, hatching performance, embryo development, right ventricular (RV) to total ventricular (TV) ratio, and blood parameters. The highest egg water loss and embryonic mortality and the lowest hatchability were in the H0−11 group, which depended on increased eggshell temperature during incubation. On day 18 of incubation, due to the decreased egg water loss in the O12−21 and O18−21 groups, there was an increase in hatchability in fertile eggs similar to the middle and late H groups. Towards the end of incubation, embryo/chick weights were not different and RV and TV weights increased in the treated groups, and the RV ∕ TV ratio changed between 15 and 26 %. At hatching, yolk sac weight increased in H0−11 and H12−21 groups. The O groups had the lowest serum tri-iodothyronine (T3) concentration as distinct from H groups. The serum thyroxine (T4) concentration increased in the treated groups, dependent on sex of the embryo. Blood hemoglobin concentration of O groups decreased relative to other groups. The hematocrit value was the lowest in the O12−21 and highest in the H12−21 groups. The H and O treatments during pre-hatch hypoxic HA condition can be positively evaluated on physiological traits of embryos after half of incubation depended on the timing of the IC exposure to the hatching eggs obtained from broiler breeders at sea level.

Maternally derived yolk antioxidants buffer the developing avian embryo against oxidative stress induced by hyperoxia

In oviparous animals, maternally transferred antioxidants protect the embryo from oxidative damage from high rates of reactive oxygen species (ROS) production incurred by rapid growth. Elevated ROS exposure – beyond that incurred by normal growth - can occur as a result of exposure to exogenous factors (e.g. pollutants, toxins, radiation), increasing the risk of oxidative damage, with potentially adverse consequences for embryonic development and long-term fitness. The capacity of the avian embryo's antioxidant protection system to counter an increased exogenous oxidative threat is poorly understood. We induced an external oxidative challenge via experimental increase in ambient oxygen concentration throughout incubation of wild great tit Parus major eggs in the laboratory. At day 11 of incubation, brain tissue revealed no consistent differences in oxidative stress status – as measured by antioxidant levels (superoxide dismutase and total glutathione), lipid peroxidation and telomere length - between control (21% oxygen) and hyperoxic (40% oxygen) embryos. However, the level of vitamin E was significantly lower and lipid peroxidation was significantly higher in yolks of eggs reared under elevated oxygen concentrations. The results suggest that maternally derived yolk antioxidants successfully buffer developing embryonic tissues against an increased exogenous oxidative threat. Furthermore, vitamin E plays a more important role in protecting the embryo than carotenoids. However, the depletion of antioxidants and increased peroxidation of lipids in the yolk could have negative consequences for embryonic development – in particular for the brain and heart that require highly unsaturated fatty acids - and protection against the oxidative burst following hatching.

Equilíbrio ácido-básico de embriões e pintos de corte em momentos críticos da incubação e submetidos a diferentes períodos de transferência para o nascedouro

Foram analisados os níveis de pCO2, pO2, pH e HCO3 - de embriões e pintos de corte provenientes de matrizes novas e velhas, nos momentos anteriores à bicagem interna e externa da casca e ao nascimento, submetidos a diferentes períodos de transferência para as condições ambientais dos nascedouros. Os tratamentos foram definidos pela idade da matriz (33 e 63 semanas) e pela transferência para o nascedouro (aos 15, 17 e 19 dias). O delineamento experimental foi em parcelas subdivididas, sendo a parcela os três momentos de transferência e a subparcela as duas idades das matrizes. Foram utilizadas seis repetições para cada tratamento, e o embrião ou o pinto foi considerado uma repetição. Os dados normais e homogêneos foram submetidos às análises de variância, e as médias comparadas pelos testes F, de Tukey e SNK. Embriões cujos ovos foram transferidos aos 15 dias para o nascedouro apresentaram melhor equilíbrio ácido-básico durante as fases pré-natal e perinatal. Durante o último terço da incubação, independentemente das diferentes condições ambientais às quais os embriões são submetidos e da idade da matriz, há capacidade de resposta fisiológica que permite uma estabilidade no equilíbrio ácido-básico dos pintos após a eclosão.

Physiological relationships of the early posthatch performance of broilers to their embryo and eggshell characteristics

Relationships between physiological parameters of early posthatch chicks with their corresponding egg and embryo parameters were examined in progeny of young broiler breeders. Four hundred and 80 broiler hatching eggs that were obtained from a 29-wk-old Ross 308 breeder flock were incubated on 8 replicate tray levels of an incubator until hatch. Between 10.5 and 18.5 d of incubation, internal (T(emb)) and external (T(ext)) egg temperatures were recorded twice daily using temperature transponders. Beginning at 18.5 d, the eggs were individually monitored for hatch every 12 h. Average T(emb), T(ext), and average daily incubational egg weight loss (EWL) for the 10.5- to 18.5-d incubation period were used to calculate eggshell water vapor conductance (G(H2O)), specific G(H2O) (g(H2O); G(H2O) adjusted to 100 g of set egg weight basis), and a G(H2O) constant (K(H2O)) for each egg. Chicks were grown out for 10 d in pens of a single battery brooder. In each pen, on d 3 posthatch, carcasses, yolk sac, liver, and pipping muscle samples were collected from at least 2 chicks that hatched from eggs implanted with transponders for determination of their relative weights and moisture concentrations. Livers and pipping muscles were also analyzed for glucose, glycogen, fat, and protein concentrations. Yolk sac weight as a percentage of chick BW (YW) and its moisture concentration (YSM) were positively correlated with T(emb). Egg g(H2O) was positively correlated with chick carcass moisture concentration and its relative weight as a percentage of set egg weight, but it was negatively correlated with YW. The positive functional relationship between T(emb) and incubation length may be mediated via their common positive relationships to YSM. A negative correlation was observed between percentage EWL and relative BW on d 0 and 0.5 posthatch for chicks hatched from unimplanted eggs. The results suggest that a higher g(H2O) results in an increased metabolism of the broiler embryo, which subsequently increases growth and yolk sac absorption in broiler chicks through 3 d posthatch.

Standardization of egg collection from aquatic birds for biomonitoring--a critical review

Collecting bird eggs is an established method of biomonitoring for specific pollution hazards. One of the most critical problems with this method is the extreme biological variability in bird eggs, but standardizing the collection and preservation of eggs can reduce these problems. Furthermore, standard practices are required so that the results can be compared among studies because mistakes cannot be corrected by laboratory analysis. Therefore, a standard procedure for collecting and preserving bird eggs may be necessary. The objective of this review is to investigate the current standard of quality assurance in the field by analyzing 86 peer-reviewed papers describing egg collection and use for aquatic birds. We show that little attention has been paid to standardizing how eggs are collected and stored in the field. Important information is often absent, including crucial aspects of sample collection and preservation, such as the freshness of the eggs, the position of the eggs in the laying sequence, the selection criteria, random sampling, and the duration and temperature of transport. Potential standards are suggested and discussed as a foundation for the development of quality assurance standards in the field.

Effect of eggshell temperature and oxygen concentration on survival rate and nutrient utilization in chicken embryos

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.

Influences of hypoxia on hatching performance in chickens with different genetic adaptation to high altitude

The experiments were conducted to assess how hatching performance is affected by chicken breeds and environment of high altitude and to analyze the vital factor of the low hatchability at a 2,900-m altitude. Eggs of Tibetan and Dwarf chickens were incubated at conditions of normobaric normoxia, normobaric hypoxia, hypobaric hypoxia, and supplemental O2 at high altitude (hypobaric normoxia) during the whole incubation or at 0 to 7, 8 to 14, and 15 to 22 d of incubation, respectively. The results showed that the Tibetan chickens had greater hatchability (79.72%), lower water loss (12.90%), greater relative embryo weight (38.08%), and relative chick weight (68.41%) compared with the Dwarf chickens (31.69, 15.79, 30.71, and 65.21%, respectively) when both of them were incubated at a 2,900-m altitude. The hatchability was 71.60% in Tibetan chicken and 36.23% in Dwarf chicken under the normobaric hypoxia condition. The hatchability of chicken was efficiently increased with supplemental O2. The previous results indicated that the O2 deficit is the main factor resulting in the low hatchability and the poor chick quality of the lowland chicken breed when incubated at a 2,900-m altitude. Breeding chickens for adaptability to hypoxia and supplemental O2 is a good way to improve the hatchability and chick quality at that altitude.