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South African Journal of Animal Science

On-line version ISSN 2221-4062
Print version ISSN 0375-1589

S. Afr. j. anim. sci. vol.51 n.2 Pretoria  2021 



Effects of ventilation programme and eggshell thickness on hatchability rate and hatching time of broiler eggs



N. Okur#; S.A. Eratalar

Poultry Science Department, Faculty of Agriculture, Bolu Abant Izzet Baysal University, Bolu, Turkey




The aim of the research was to determine whether enrichment of the atmosphere in an incubator with carbon dioxide (CO2) and oxygen (O2) and eggshell thickness (EST) affected embryonic death (ED), hatchability of fertile eggs (HFE) and hatching time (HT). A total of 320 Ross 308 eggs were used and the experiment was repeated twice. Eggshell thickness was classified as thin (<31 μηι), medium (31 - 32 μηι) and thick (>32 μπι). The incubators were operated with their internal atmosphere enriched with CO2 (1.57% CO2; 20.23% O2) or O2 (0.50% CO2; 22.44% O2). Embryonic death, HFE and HT data were monitored at three periods, namely early (<486 hours), middle (486 - 492 hours), and late (492 - 510 hours). Early ED, late ED and hatchability of fertile eggs were not affected by EST or by the incubator's internal atmosphere (P >0.05). Thus, O2 supplementation to the incubator was deemed unnecessary at 822 m altitude. There was a highly significant interaction between EST and HT. Eggs with shells 31 to 32 μπι thick hatched at an appreciably greater rate between 486 and 492 hours of incubation (17%) than eggs with thicker (0.6%) or thinner (0.4%) shells in both the CO2 and O2 enriched atmospheres. The hatching rate was significantly higher in the eggs with an intermediate EST than in thick-shelled eggs. A greater proportion of eggs hatched at the late HT as opposed to earlier, regardless of EST.

Keywords: broiler, eggshell thickness, hatching time, incubator ventilation programme




Successful incubation of broiler eggs depends on management of the incubator (French, 1997; Yildirim & Yetisir, 2004) and certain characteristics of hatching eggs such as genetics, age, maintenance and feeding conditions of breeders, egg weight (EW), and EST (Kirk et al., 1980; Narushin & Romanov, 2002; Sarica et al., 2012; Elibol & Turkoglu, 2014; Hammershoj & Steenfeldt, 2015; Yamak et al., 2015; Popova et al., 2019). The levels of CO2 and O2 in the incubator reportedly determine the rate of embryonic development and may affect incubation and post-hatching performance (Metcalfe et al., 1981; Lourens, 2007; Molenaar et al., 2010; Tona et al., 2013).

An atmosphere that is low in O2, such as at high altitudes, can affect incubation efficiency and chick quality negatively (Ahmed et al., 2013. The content of O2 in the atmosphere is about 21% at sea level (Stock & Metcalfe, 1984). Low (<17%) and high (25%) O2 levels have both been reported to affect embryonic survival and hatchability negatively (Stock & Metcalfe, 1984; Lourens et al., 2007; Molenaar et al., 2010). In high altitude (3500 - 4000 m) areas, such as India and South America, very low hatchability rates have been reported such as 20% (Ahmed et al., 2013; Tullet 2013). To compensate for reduced levels of O2, an oxygen concentrator can be used to increase the oxygen level of the atmosphere inside the incubator (Cobb, 2013; Tullet, 2013).

Researchers reported favourable effects from an increase in the level of CO2 in the incubator. A gradual increase of up to 1.5% in CO2 levels, which should normally be around 1% in the first 10 days of incubation, improved embryo development, promoted early hatching, and increased overall hatchability (Buys et al., 1998; Onagbesan et al., 2007; Tong et al., 2015).

Eggshell thickness has an important role as an embryonic respiratory component (Hunton, 2005). It can be measured with non-destructive equipment that is produced by a few innovative companies (e.g. Orka Tech Ltd., Israel). Eggshell thickness varies between 33 and 40 μm in broiler eggs (Yamak et al., 2015). In addition, EST in the range of 35 - 39 μm (Huwaida et al., 2015) apparently does not affect embryo mortality or hatchability.

Because of their potential effects on economic criteria, including hatchability of fertile eggs and hatching time, it was hypothesized that differences in the CO2 and O2 levels of the atmosphere inside the incubator and their interrelationship with EST will affect embryonic survival, hatchability of fertile eggs and time of hatching of broiler chicks.


Material and Methods

The study was conducted in accordance with the Turkish Animal Welfare Act, and all procedures involving handling of eggs and chicks were approved by the Animal Ethics Committee of Bolu Abant Izzet Baysal University (Decision no: 2015/45 dated 30 December 2015). It took place in Bolu Province where more than 30% of poultry production in Turkey occurs. The average altitude of this province is 822 m.

The entire experiment was done twice under identical conditions. In each experiment, 2880 broiler hatching eggs were obtained from Ross 308 breeder flocks. All eggs were stored for three days before incubation, and the egg storage room was kept at 18 °C and 75% relative humidity during this period. Before the incubation period, the eggs were preheated for six hours in incubators set at 24 °C.

The eggs were weighed and classified as heavy (69.83 ± 0.25 g), medium (65.10 ± 0.10 g), and light (60.97 ± 0.21 g), and placed in trays so that there was an equal number of eggs of similar weight in all treatment groups. The incubators (Cimuka 960SH, Cimuka Ltd. Co., Turkey) were located in the incubation laboratory of Bolu Abant Izzet Baysal University Faculty of Agriculture Department of Poultry Science. Each incubator was equipped with six egg trays with a capacity of 80 eggs, and six chick baskets with the same capacity. The six trays were divided into groups of two, according to their location in the incubator. The eggs that were used in this research were positioned in the middle part of each tray. Therefore, 320 hatching eggs were weighed (± 0.1 mg) individually using an analytical balance (Radwag AS 220.R2, Radwag Balance and Scales, Poland) and numbered. Eggshell thickness was measured with an ultrasonic EST gauge (Orka Tech. Ltd., Israel) with a sensitivity of ±1 μm and classified as thin (<31 μm), medium (32 - 33 and thick (>33 μm). During the incubation period, both incubators were operated to achieve 37.8 °C eggshell temperature.

To achieve a CO2-rich atmosphere in one of the incubators, the ventilation flaps were closed during the first 10 days of incubation and CO2 was allowed to increase. After this time, the ventilation flaps were opened and the normal ventilation regime was applied. In the second incubator, an O2-rich atmosphere was achieved with an oxygen concentrator (Hikoneb Oxybreath 10LPM, Kare Medical Ltd. Co., Turkey), which produced 92 ± 3% pure O2 and was introduced at approximately 10% of the total air drawn into the incubator. The CO2 level was measured with Hatch Eco2-01 sensors (Cimuka Ltd., Turkey), and the O2 levels were recorded by PAC 7000 data loggers (Drager Safety AG & Co., KGaA, Germany). Eggshell temperature values were measured with an infrared ear thermometer (Braun Thermoscan, Braun, Germany). In both incubators relative humidity was maintained at 57.0% throughout the incubation period. The trays were turned automatically 24 times a day.

On the 18th day of incubation, the eggs were transferred from the trays to the hatching baskets in the same incubators and maintaining their position. The experimental eggs were held in a specially prepared plastic compartment that was covered to maintain the association of eggs and chicks with the treatment to which they had been subjected. Hatching time was categorized as early, middle, and late. To determine HT, the incubators were opened after 486, 492, and 510 hours of incubation. At these times, the eggs were checked, and hatched chicks were counted, recorded, and removed. Hatching rates for each treatment were calculated as:

Once hatching was finished, EDs were determined as early (0-5 days), middle (6-17 days) and late (18-21 days, and as pipped but unhatched eggs). Percentages of early-, middle-, and late-stage EDs were calculated relative to the total number of eggs set. The percentage hatchability of fertile eggs was expressed relative to the total number of fertile eggs set.

The required number of observations was calculated with PASS 11 (Hintze, 2011) power analysis. The data were analysed using IBM SPSS Statistics 22 (SPSS Inc., 2013). The Shapiro-Wilk test was used to confirm the normal distribution of the data. One-way analysis of variance and post-hoc Tukey test were used to assess the treatment effects. P-values lower than 0.05 were considered significant. The results are reported as means ± standard error.


Results and Discussion

The data in Table 1 confirm the categorization of EW as heavy, medium and light and EST as thin, medium and thick. Likewise, they demonstrate the similarity of eggs that were allocated to the treatments (P >0.05). Overall, the average EW was 65.17 g with a coefficient of variation (CV) of 6.17 and the average EST was 31.26 μm with a CV of 4.34. In the light of these data, the uniformity of the eggs used in the present research was high. These eggs were slightly heavier than those used by Kirk et al. (1980) and had thinner shells compared with other studies (Christensen et al., 1994; Huwaida et al., 2015 and Yamak et al., 2015).

In the first 10 days of incubation, the atmosphere inside the incubator could be enriched gradually with CO2 by keeping the ventilation flaps closed (Figure 1). Thus, on the tenth day of incubation, eggs in that incubator were exposed to a CO2 level of 1.50% and an O2 level of 20.25%. In contrast, eggs in the incubator in which the atmosphere was enriched with O2, were exposed to a CO2 level of 0.90% and an O2 level of 21.50% at that time.

Enriching the atmosphere inside the incubator with either CO2 or O2 through day 10 of incubation did not affect (P >0.05) the levels or timing of ED or HFE (Table 2). These results differ from the observations of Tona et al. (2013), in which a gradual increase in level of CO2 up to 1.50% improved embryo development, promoted early hatching, and increased the hatchability of chicken eggs. However, the broiler breeding companies indicated that O2 enrichment of the atmosphere inside an incubator should not be expected to alter embryo development or hatchability in places with an altitude less than 1000 m above sea level. The location in which the current study was conducted is 822 m above sea level (Cobb, 2013; Tullet, 2013). Accordingly, it can be concluded that in areas with similar altitude, the use of an oxygen concentrator to maintain the O2 level in the incubator is not necessary. Eggshell thickness did not affect the timing and level of ED or HFE (P <0.05). This result was consistent with the findings of Huwaida et al. (2015), who reported that EST did not affect ED and hatchability. The interaction of EST and atmospheric conditions in the incubator did not affect these traits (P >0.05), either.

The highly significant interaction effect resulted primarily from eggs with shells 31 to 32 μm thick, which had an appreciably greater rate of hatching between 486 and 492 hours of incubation than eggs with thicker or thinner shells in the CO2- and O2-enriched atmospheres (Table 3). In addition, eggs with this intermediate shell thickness hatched at appreciably higher rates than thin- or thick-shelled eggs. A greater proportion of eggs hatched at the late HT than at the earlier time, regardless of EST. For the late hatching, the hatching rate was significantly higher in eggs with an intermediate EST than in thick-shelled eggs.

Prolonged holding of chicks without food and water in an incubator can lead to their becoming dehydrated and losing weight. The results for the effect of EST show that it is an important parameter of egg quality (Ketta & Tumova, 2016; Dahloum et al., 2018; Ketta & Tumova, 2018) and of HT. It is known that EST decreases as the egg yield increases (Christensen et al., 1994; Yamak et al., 2015). Modern technology allows non-destructive measurement of EST (Khaliduzzaman et al., 2020; Kibala et al., 2015) and could be used in managing the incubation process. An alternative way of reducing holding time would be to empty the incubators twice instead of once.



Although they are beneficial at higher altitudes, changes in the internal atmosphere of the incubators were deemed unnecessary at 822 m altitude. However, HT was affected by EST, and the incubation process might be made more efficient and the welfare of hatched chicks could be improved by sorting the eggs according to EST when placing them in an incubator.



This research was supported by BAP Project No. 2016.10.03.990 awarded to Bolu Abant izzet Baysal University (BAIBU) and the equipment was provided by this project and additional funding (BAP project numbers 2015.10.03.881, 2015.103.88 and 2016.10.03.1029). The BAIBU and Beypi Inc. (beypilig®) for their support which allowed the first author to realize the research.

Authors' Contributions

NO designed the study and analysed data. NO and SAE collected data and prepared the manuscript.

Conflict of Interest Declaration

The authors declare that they have no affiliations with any organization or entity with any financial or non-financial interest that could bias the subject matter and outcomes discussed in this manuscript.



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Submitted 23 August 2019
Accepted 10 October
Published 9 March 2021



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