Introduction
The level of relative humidity (RH) and turning inside the incubators and hatchers is one of the main factors for successful day-old chick production. The egg consists of 75% water and, during embryonic development, water must be partially lost through the eggshell pores along a gradient, i.e. from high humidity (usually inside the egg), to low humidity (the environment outside the egg). According to Tullett (Reference TULLETT1990), as breeder age increases so does the conductivity of the shell. The conductivity term was conceptualised by the author as the ability of the shell to allow gaseous exchange and water vapour between the embryo and the environment, and directly relates to the pore number and size, eggshell thickness, strength, and the conditions of the environmental incubator. The drier the air is around the egg, the greater the evaporation rate. For this reason, the humidity around fertile eggs must be controlled to ensure proper embryonic development (Decuypere, Reference DECUYPERE2001). During incubation, oxygen diffuses into the egg, and is used by the embryo during its development. Accordingly, water and carbon dioxide produced by the embryo are eliminated, and these two processes are proportional and simultaneous. The loss of moisture from the embryo to the external environment enables an increase in air chamber volume (North and Bell, Reference NORTH and BELL1990; Taylor, Reference TAYLOR1999). By the time the chick pecks or pierces the air chamber, the chamber needs to be of adequate size for the chick to successfully transition from chorioallantoic to pulmonary respiration (Salazar, Reference SALAZAR2000). Some authors indicate that the RH in the incubator should be set between 56 to 60% for broiler breeder eggs, which have a loss of approximately 12% moisture during the first 18 days of incubation. Eggs which lose about 11 to 13% of their initial weight at this stage have better rates of hatching, as compared with eggs that have less weight loss (Tullett, Reference TULLETT1990; Mauldin and Buhr, Reference MAULDIN and BUHR1995; Brake, Reference BRAKE1996; Christensen, Reference CHRISTENSEN1997; Rosa et al., Reference ROSA, SCHEUERMANN and FIGUEIREDO1999). According to Marques (Reference MARQUES1994), the RH at hatch should remain above that of incubation. According to Taylor (Reference TAYLOR1999), Salazar (Reference SALAZAR2000) and Decuypere et al. (Reference DECUYPERE, MALHEIROS, MORAES and BRUGGEMAN2003), if the RH in the incubator is too low, there will be excessive loss of moisture from the embryo, affecting the hatchability and resulting in small and dehydrated chicks. On the other hand, if the RH is too high in the incubator, the embryos tend to hatch early, and wet residual albumen may be present. In extreme cases, the chicks can hatch without achieving full development. These authors reported that the unintended consequences of using inadequate RH levels during the incubation process could extend the growing period, as chick quality is compromised.
Another point to note is that under natural conditions the position for an egg during incubation is fully horizontal, though the hen turns the eggs frequently. In artificial incubators, the position of eggs during the first 18 or 19 days of incubation is with the wide end upwards, i.e. the air chamber facing up. For most modern incubators turning is automatic, occurring every hour at 45°. After transfer to the hatchery, the eggs are laid in a horizontal position in the hatching trays and the turning process is discontinued (Decuypere, Reference DECUYPERE2001). The benefits of turning eggs during incubation include preventing premature adhesion of the embryo and the yolk to the shell membrane, reducing distortions in the embryo positioning, complete closure of the chorioallantoic membrane in the thin end of the egg and to ensure proper use of albumen from the developing embryo (Tullett and Deeming, Reference TULLETT and DEEMING1987; Tullett, Reference TULLETT1990; Tona et al., Reference TONA, ONAGBESAN, DE KETELAERE, DECUYPERE and BRUGGEMAN2003). Tullett and Deeming (Reference TULLETT and DEEMING1987) stated that the delay in hatch or the inability of embryos to hatch which did not undergo turning is not related to egg weight, shell porosity or weight loss during incubation, but the development of the yolk sac membrane and the extent of albumen absorption which are completed at approximately 12 to 13 days of incubation. Baggott et al. (Reference BAGGOTT, DEEMING and LATTER2002) pondered the importance of turning in the formation and composition of sub-embryonic fluid which is closely linked to growth of the vasculosa area of the yolk sac membrane. According to Deeming (Reference DEEMING1989) and Wilson (Reference WILSON1991), the critical period for egg turning extends from three to seven days of incubation. During this period, the lack of turning may have a downside in gas exchange through the chorioallantoic membrane, as the unabsorbed albumen stands between this membrane and the inner shell membrane, preventing the expansion of the area vasculosa, reducing the exchange of gases between the embryo and the external environment. Pearson et al. (Reference PEARSON, HAQUE, HOU and TAZAWA1996) found physiological differences between embryos with or without turning during the incubation period, with oxygen consumption rate and the heart rate of unturned embryos being significantly lower when compared to embryos of eggs that had undergone turning. Tona et al. (Reference TONA, ONAGBESAN, BRUGGEMAN, MERTENS and DECUYPERE2005) supported these claims, reporting decreased arterial oxygen pressure in embryos during late incubation and increased haematocrit values and thyroid hormones levels. According to the authors, research on the duration, frequency and turning angle have suggested that these factors influence both embryo and chick physiological parameters, interfere with the incubation yield, raising performance but also interact with line and breeder age.
Relative humidity
When incubating broiler breeder eggs of the same weight at different levels of RH (50% and 33%), Tullett and Burton (Reference TULLETT and BURTON1982) found higher chick weights after hatching and less weight loss during incubation, when eggs were incubated with higher levels of RH. However, the yolk sac weight was not significantly affected by RH, with average weights of 8.85 g and 8.63 g when the eggs were incubated with 50% and 33% RH, respectively.
French and Tullett (Reference FRENCH and TULLETT1991) suggested that, to obtain better incubation yields, the RH may be adjusted during incubation based on the breeder age. Two experiments were conducted, in the first, the effects of two RH levels in the incubator (50 and 58%) on the hatchability of broiler breeders eggs during the period of 28 to 64 weeks of age were investigated, and the authors concluded that the younger the breeder, the better the hatching rate, and the lower the early embryonic mortality in lower RH (50%). Eggs of breeders at 60 weeks of age incubated at 58% RH presented better hatchability and lower late embryonic mortality. In the second experiment, the authors evaluated the same levels of humidity, but used eggs from breeders at 34 and 66 weeks of age. The eggs originated from breeders at 66 weeks had lower hatchability, and the younger breeder eggs had the best results at the lowest RH in the incubator (50%). Eggs from the younger breeders offered a greater resistance to the diffusion of gases and water vapour when subjected to a lower humidity, alluding to more difficult gas and water vapour exchange during incubation. However, as the eggs of older breeders do not have the same resistance, the lower RH in incubation will result in lower hatchability, due to excessive weight loss (Vick et al., Reference VICK, BRAKE and WALSH1993).
In order to evaluate the effects of incubator RH and breeder age on egg weight loss and hatchability from one to 18 days of incubation, Buhr (Reference BUHR1995) worked with Hy-Line® breeders aged 34 and 49 weeks, with eggs incubated in different RH settings. For eggs from 34 week old breeders, the percentage of weight loss were 16.6, 12.7 and 9.1%, and for eggs from breeders at 49 weeks of age, losses were 18.2, 13.6 and 9.6%, using RH levels of 40, 55 and 70%, respectively. Regardless of breeder age, the lower the RH, the greater the weight loss. In relation to hatchability, the best result was obtained with the eggs from broiler breeders at 34 weeks of age incubated at 55% RH. On the other hand, the RH in the incubator had no significant influence on the hatchability in eggs produced by 49 week old broiler breeders.
Bruzual et al. (Reference BRUZUAL, PEAK, BRAKE and PEEBLES2000a) investigated the effects of different RH levels (43, 53 and 63%) during incubation and hatching on the incubation yield and chick hatching weights with eggs from young breeders (26, 28 and 30 weeks of age). Chick weights at hatch were significantly better at higher RH in the incubator and increasing breeder age. Although chick weight was greater when eggs were incubated with higher RH, this may have an adverse effect on embryonic development and hatchability, with increased late embryonic mortality in eggs incubated with RH levels of 63% and 53%.
Hatchability and broiler performance were evaluated in broiler breeders between 26 and 31 weeks of age, whose eggs were incubated with different RH (43, 53 and 63%), during the 16th to 21st day of incubation (Bruzual et al., Reference BRUZUAL, PEAK, BRAKE and PEEBLES2000b). There were no significant differences of RH on hatchability. However, the best performance, with respect to weight gain, feed conversion and mortality rate, was achieved with 53% RH at the end of the incubation period, regardless of breeder age. Working with young breeders, Peebles et al. (Reference PEEBLES, BURNHAM, GARDNER, BRAKE, BRUZUAL and GERARD2001) suggested there a depression in embryogenesis when RH was reduced to 43% in the incubator. This may also result in poor performance and loss in chick quality after hatching.
The effects of breeder age, the relative humidity in the incubator and egg weight on hatchability, egg weight loss until transfer to the hatchery and embryo mortality were studied (Rosa et al., Reference ROSA, GUIDONI, LIMA and BERSCH2002). Broiler breeders aged 34, 39, 53 and 63 weeks, selected by egg weight classes (averages 60.0, 65.1, 66.6, 69.0 and 73.2 g), and incubated at RH levels of 51, 56 and 61% were studied. Regardless of the incubator RH level, a reduction in hatchability was observed for breeders at an advanced age. Incubator RH of 51% allowed the optimisation of hatchability and reduced embryonic mortality, irrespective of breeder age and egg weight. However, an RH of 61% for eggs from broiler breeders more than 53 weeks-old was associated with increased embryonic mortality.
Eggs incubated at different temperatures, as determined using the wet bulb thermometer (29.4°C / 84.9°F and 27.6°C / 81.7°F), showed a ratio of heart weight/chick weight at hatch of 0.78% at the lowest RH for incubation and 0.82% at the highest, although this was not statistically different (Wineland and Christensen, Reference WINELAND and CHRISTENSEN2003).
Barbosa et al. (Reference BARBOSA, CANÇADO, BAIÃO, LANA, LARA and SOUZA2008), studying the effects of incubator relative humidity and breeder age on hatchability and progeny performance, used three levels of RH (48%, 56% and 64%) and eggs from breeders of three ages (26, 41 and 56 weeks). The best rates of hatching occurred when eggs were subjected to 56% RH, regardless of breeder age, and eggs from breeders of 26 and 41 weeks showed the best results regardless of the RH. However, regarding progeny performance, no significant differences were found (Barbosa, Reference BARBOSA2005).
Monitoring incubation yield from breeder eggs during the first production cycle and after moulting, Meir and Ar (Reference MEIR and AR2008) established that, to preserve incubation within the normal range of weight loss and hatchability, the RH of the incubator should be increased gradually with breeder age, from 53% to 66% in the first production cycle. After moulting, the eggs should be incubated at a RH of 61% and increased over the production period to 67%. Regardless of the production cycle, better hatchability was achieved when eggs lost about 12 to 13% of their weight in the first 18 days of incubation.
Turning
effects of turning duration
Studying the turning period of incubating eggs on hatchability and post-hatching chick performance, Proudfoot et al. (Reference PROUDFOOT, HULAN and McRAE1981) found no evidence of effects on hatchability when turning was employed up to 13 days of incubation. Chick performance was not affected when turning was terminated at 16 days of incubation. Wilson and Wilmering (Reference WILSON and WILMERING1988) conducted experiments with broiler breeder and breeder hens eggs subjected to periods of turning up to 10, 13, 16 and 19 days in the incubator. The incidence of poor embryo positioning was not affected by treatments. The authors concluded that the turning could be discontinued for 16 days without causing decreased hatchability.
In a study by Tona et al. (Reference TONA, DECUYPERE and COUCKE2001), eggs from Hybro®, Cobb® and Ross® breeders between 27 and 75 weeks, were transferred to the hatchery with 15, 16, 17 or 18 days of incubation. The best hatchability was observed in eggs transferred at 18 days when compared to other treatments. However, hatchability differences of eggs transferred at 15, 16 and 17 days were not significant. The percentage of unhatched eggs increased with breeder age and was affected by strain, with the Hybro® line hatchability and from older breeders (over 51 weeks) being most affected by the anticipation of the transfer. The authors recommended that, in addition to individual characteristics of each strain, the time of transfer shall be considered to optimise hatchability and chick quality, especially when eggs from old breeders are incubated.
Tona et al. (Reference TONA, ONAGBESAN, DE KETELAERE, DECUYPERE and BRUGGEMAN2003) used Cobb® eggs from breeders aged between 28 and 58 weeks to assess the effects of the turning length (up to 12, 15 or 18 days of incubation) on the corticosterone levels, the thyroid hormones levels, the partial pressure of gases in the air chamber at the time of internal pipping and production parameters. The corticosterone level increased from 15 days of incubation until the hatching time, but there was no significant difference between treatments, indicating that this hormone had no influence on the parameters studied in the experiment. Turning up to 18 days of incubation increased embryo T3 and T4 levels, suggesting increased metabolic activity with a consequent reduction in the oxygen concentration and increased carbon dioxide in the air chamber. Better hatchability (90.4%) was seen when turning eggs up to 18 days of incubation as compared to eggs turned for up to 15 days (86.4%). However, turning for up to 12 days of incubation resulted in 88.7% hatchability, which was statistically similar to turning up to 15 and 18 days. Hatching chick weight was similar among treatments; however the weight loss at seven days-old significantly increased as the turning duration. It was hypothesised that, in unturned eggs, the use of the yolk is reduced, and longer periods of turning promote rapid and excessive yolk utilisation which may result in lower performance in the first week post-hatch.
In order to evaluate the effect of turning duration in three periods of embryonic development (zero to seven, eight to 14 and 15 to 18 days) on the incubation yield, Elibol and Brake (Reference ELIBOL and BRAKE2004) used Ross 308® breeder eggs aged 29 and 68 weeks. The authors tested the combinations of the presence or absence of these three turning periods. The absence of turning from zero to seven days of incubation showed the greatest negative effects on hatchability, which were most pronounced in eggs from older breeders, with high initial incubation mortality. Delayed embryonic growth and development was evidenced in the final two thirds of incubation by increased intermediate and late mortality and poor positioning problems. When turning was not made in the first week of incubation, the embryo or the extra-embryonic membranes adhered to the eggshell membrane, preventing proper chorioallantoic membrane growth and caused abnormal development or death of the embryo. The increase in albumen viscosity restricts the blood supply expansion to the embryo and leads to the formation of a ‘ring of blood, commonly seen in mortality cases at five days of incubation. With turning in the first week, the absence or presence of this procedure in the remaining days of incubation revealed no significant differences, demonstrating that if turning is continued after seven days of incubation this possessed little or no benefit regarding embryonic mortality. Absence of turning up to seven days of incubation resulted in exacerbation of these deleterious effects. Regardless of turning treatments, a lower hatching was observed for 68 weeks-old breeders as compared to 29 weeks-old breeders.
Tona et al. (Reference TONA, ONAGBESAN, BRUGGEMAN, MERTENS and DECUYPERE2005) incubated eggs from Cobb® breeders to study the effect of turning duration on the albumen utilisation and embryo weight. The treatments were defined by the absence of turning or turning maintained to nine, 12, 15 or 18 days of incubation. Turning increased albumen utilisation, possibly related to embryonic growth, as unturned embryos had lower weights and higher residual albumen. Incubation up to 12 days was sufficient for complete albumen absorption and higher weight embryos occurred at 15 and 18 turning days, with turning causing a stimulating effect on the embryonic growth rate which should be maintained at least for the first 15 days of incubation.
Mahmud and Pasha (Reference MAHMUD and PASHA2008) studied the effect of pre-heating and turning during the holding period on the hatchability of broiler breeder eggs. The eggs from 32 week-old breeders were divided into four groups: without turning and pre-heating, no turning but pre-heated, turned but without pre-heating and both pre-heating and turning. The pre-heating of eggs was performed in an incubator with hot air at a temperature of 30°C (86°F). The eggs were turned on an hourly basis at an angle of about 45° until 17 days of incubation, but no significant differences were found between treatments.
effects of turning frequency
Eggs from Ross® breeders of 37, 41, 59 and 63 weeks of age were subjected to three daily turning frequencies (24, 48 or 96 times) between the third and 11th day of incubation (Elibol and Brake, Reference ELIBOL and BRAKE2003). From one to two and 12 to 18 days, eggs were turned 24 times daily. Fertile egg hatchability was higher for eggs from younger breeders (37 and 41 weeks) when compared to older breeders (59 and 63 weeks of age). Eggs from breeders of 59 and 63 weeks of age had a higher initial (zero to six days) and late (18 to 21 days) mortality. A greater hatchability was observed for eggs subjected to 96 turns per day, mainly due to a decrease in the percentage of late death. Late embryonic death could be related to abnormal chorioallantoic membrane development due to growth delay and lack of turning in the early stages of incubation.
Investigating the influence of the turning frequency during the second week of incubation Elibol and Brake (Reference ELIBOL and BRAKE2006b) used eggs from Ross 308® breeders of 34 and 37 weeks of age; considered ‘young’, and 59 and 61 weeks; classified as ‘old’. Eggs were subjected to two frequencies (24 and 96 turns per day) and four periods of turning (up to 8, 10, 12 or 14 days of incubation). The best hatchability was observed in eggs from younger breeders regardless of the turning frequency and period of incubation. There was no significant difference between the turning periods applied in the experiment, indicating that the turning could be discontinued from eight days of incubation. Turning 96 times daily increased hatchability significantly, mainly due to the interaction between breeder age and frequency of turning, due to reduced late embryonic mortality in eggs from older breeders. Increased turning frequency and egg quality are breeder age-associated subjects of interest, especially for older breeders.
Elibol and Brake (Reference ELIBOL and BRAKE2008), examined the effect of the eggs position and storage duration associated with the subsequent turning during incubation on hatchability and embryonic mortality of eggs from broiler breeders at 60 and 62 weeks of age. The eggs were arranged with the blunt end facing up or down for 3 or 14 days of storage, and after these periods, were incubated with a turning frequency of 24 or 96 times per day during the first 18 days of incubation. Longer periods of storage caused a decrease in hatchability independent of the other variables. There was an interaction between egg positioning and storage for 14 days. Eggs stored with the blunt end down had better hatchability. This result may be related to the fact that in periods of prolonged storage, this position leads to more centralisation of the yolk sac, located in the equatorial region of the egg blastoderm, preventing embryonic mortality in the first days of incubation. In the same period of storage, it was also observed that turning eggs 96 times per day significantly improved hatchability. This was justified by the possibility of better interaction of the blastoderm with fresh albumen at increased turning frequency during periods of prolonged storage. Data from this experiment suggested that the harmful effects of prolonged storage can be mitigated by both the inverted position of the egg during this period, and the subsequent increase in the turning frequency during incubation.
effects of the turning angle
French (Reference FRENCH1997) suggested that reducing the turning angle could increase the space and facilitate the air flow between the incubator trays, benefiting the egg's ventilation and resulting in a reduced air velocity being required within the incubation machine, since the distance between the trays is reduced during the turning when compared to the distance between them in a horizontal position.
In a first experiment, Elibol and Brake (Reference ELIBOL and BRAKE2006a) incubated eggs from Ross 308® breeders of 55 and 57 weeks of age in three turning angles, 35°, 40° and 45°. Eggs were subjected to 24 turns per day until the day of transfer. The incidence of malpositioned embryos increased with turning made at an angle of 35°, compared to turning at an angle of 40° and 45°, which were similar, although angles were not sufficient to alter hatchability.
In the second experiment, eggs from breeders of 57 and 61 weeks of age were turned at angles of 35° and 45°, at two frequencies for the 35° angle (24 and 96 times daily) and 24 turns daily at the 45° angle. The incidence of malpositioned embryos was increased with the turning angle of 35° at a frequency of 24 times a day compared with the other two treatments, which were similar. However, hatchability was not impacted by the turning angle. The authors concluded that the turning angle did not affect hatchability and the incidence of malpositioned embryos can be ameliorated by a concomitant increase in the frequency of turning.
Cutchin et al. (Reference CUTCHIN, WINELAND, CHRISTENSEN, DAVIS and MANN2009) conducted an experiment to determine the effects of a reduced turning angle on embryonic and extra-embryonic development. Turning eggs at 15° caused an increase in embryonic mortality from day 11 to 16 and day 17 to 21 and an overall decrease in hatch when compared with turning eggs at 45°. There was no difference in the area vasculosa at day three, but there was a reduced amount of sub-embryonic fluid at day six. Overall, it was determined that a reduced turning angle decreases the hatchability of fertile eggs.
Conclusions
Many factors should be considered to successfully manage relative humidity and turning machine incubators. Among these are the breeder age, strain, egg weight and eggshell conductance. In order to maximise the productivity of poultry, hatching studies involving industrial scales should be continued to determine appropriate levels of relative humidity and duration, frequency and turning angle.
