The range of hatch time was calculated as the difference between maximum and minimum hatch times. The hatch window was monitored as the time elapsed between the first and last chicks, and it included the average hatch time (h) and hatch time range (h). Hatched chicks were wing banded, weighed, and recorded as chick weight at hatch, and then placed back in the incubator after recording the hatching time. The hatcher was opened at 456 h and repeated every 4 h. At 432 h of incubation, the eggs were weighed and candled for transferring the living embryos to the hatcher. Setting eggs’ time in the incubator was determined to obtain hatch time in an hour and was considered as 0 h. Carbon dioxide concentration in the incubators was measured per hour using a CO 2 sensor (CO 2 Meter-EZTCH-GCH, 2018, USA). Gradual increase of CO 2 was allowed among the experimental treatment groups, followed by opening the incubator holes to permit ventilation until the end of the incubation periods. All eggs were incubated at 37.5☌ and 55% relative humidity during the setting phase. Ventilation holes of the incubators were closed for 3, 6, and 9 days for the rest of the treatment groups and termed as non-ventilated (NV) groups (NV1, NV2, and NV3, respectively). The first egg group was incubated in a normally ventilated (V) incubator (V) during the setting phase (0–18 days) and served as a control group. Eggs were weighed and randomly/equally divided into four incubators, whereas 1800 hatched eggs were divided into six replicates for each incubator. Hatching eggs (n = 7200) produced from Mandarah breeder chickens (an Egyptian-developed dual-purpose strain), aged 45 weeks were collected and stored for 5 days. This study aimed to determine the possible beneficial effect of non-ventilation conditions for 3, 6, and 9 days on embryonic mortality, spread of hatch, hatch time, hormonal levels, and hatchability in Mandarah breeder chickens. reported that the gradual increase of CO 2 during the first 10 days of incubation caused higher hormonal levels of triiodothyronine (T 3), tetraiodothyronine (T 4), and corticosterone and these hormones could have a cardinal role in improving hatchability and narrowing hatch time. Mortola showed that short-term hypercapnia could influence lung function causing an early pipping. mentioned that hatchability percentage and broiler chick size significantly increased with 3000 ppm CO 2 concentration. concluded that non-ventilation conditions with a circulation of CO 2 for the first 10 days of incubation are preferable to ventilation conditions for hatchability results. It decreases the barrier to the diffusion of O 2 to the embryo. Moreover, raising CO 2 levels during the first part of incubation influences albumen acidification and liquefaction along with sub-embryonic fluid formation. found that hypercapnia conditions through the first 5 days of incubation decreased albumen pH and egg weight loss.Ĭoncerning incubation conditions, previous studies have shown that non-ventilation in the first 10 days of incubation allowed a gradual increase in CO 2 up to 1.5%, and consequently reduced albumen pH, as well as enhanced embryonic growth and improved hatchability. found that 4% CO 2 could enhance embryonic growth during the first 48 h of incubation and improve amnion closure during early incubation. Carbon dioxide is an important gas in embryonic development which is released first during incubation from egg albumen as a natural reservoir and as the metabolic by-product of the embryos. Normally, the incubation conditions of oxygen (O 2) and carbon dioxide (CO 2) are 21% and 0.5%, respectively. Embryonic development is a process determined by genetic background and environmental conditions. Therefore, the poultry industry’s main goals are to improve the efficiency of incubation processes and the quality of day-old chicks. Investigating environmental conditions and their effects on the bird’s productive performance and welfare is very important for improving and advancing the global poultry industry.
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