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Incubation lighting schedule and broiler performance
Abstract
Commercial hatching eggs are incubated in complete darkness. In nature a hen will leave the nest intermittently, exposing the eggs to light. To test the effects of differing lighting schedules during incubation on chicken development, Ross 308 eggs (N = 1,005) from a 40 week old parent flock were incubated from embryonic day 0 (E0) until hatch using 1 of 3 lighting regimes: continuous light (24L), 12 hours of light, followed by 12 hours of darkness (12L:12D), or continuous darkness (24D). The type of lighting used was a 500 lux white light emitting diode (LED) with a colour temperature of 6,050K, and eggshell temperatures were maintained at 37.8°C. Chickens were grown out until day 35 post hatch. Hatch time and sex were recorded and chickens were sampled within 3 hours post hatch for body weight, length, navel score, and organ weights. Post hatch body weight, feed intake and growth:feed were determined weekly. At day 21 post hatch, or-gan weights were determined. Hamburger-Hamilton (H&H) embryonic stage, hatcha-bility, and culls at hatch were not affected by treatment. Average hatch time was affected by a treatment x sex interaction, but the most conclusive finding was the main effect of treatment: overall incubation time was shorter for 24L (490 hours) than for 12L:12D and 24D (497 hours; P < 0.001). Yolk free body mass (YFBM), liver weight, and intestine weight at hatch were higher for 12L:12D than for 24L (+0.2 g, +0.13% of body weight, and +0.42% of body weight, respectively; P < 0.031). Intestinal weight at hatch was furthermore higher for 12L:12D than for 24D (+0.34% of body weight). Organ weights no longer differed at D21 post hatch. Body weight, feed intake, and growth:feed were not different between treatments. These results suggest that 12L:12D white LED light applied during incubation at a set eggshell temperature of 37.8°C stimulated chick deve-lopment at hatch, independent of sex, when compared to a 24L regime. The stimulatory effect of 12L:12D was no longer observed during the grow out period when body weight, organ weights, feed intake, and growth:feed were investigated. To conclude, while a ligh-ting schedule of 12L:12D during incubation seems to increase embryonic development, post hatch performance parameters such as growth and growth:feed were not improved when compared to using the industry standard of 24D.
Incubation lighting schedule and broiler performance
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1 | Implications
In commercial incubation, eggs are incubated in complete darkness. Light during in-cubation may be necessary for optimal embryonic development, which may be related to later life health and productivity. In the present study, providing continuous darkness, light, or a light-dark schedule during incubation was investigated in relation to hatch-ling quality and development. This is an area that is of particular interest, both for our scientific understanding of chicken embryo physiology, and as a potential tool utilised by hatcheries for improving long term chicken development and health.
2 | Introduction
In commercial practice, eggs are incubated in complete darkness, except for the moment the eggs are candled and transferred from the setter to the hatcher. However, there is evidence to suggest that by providing light during the incubation process a positive ef-fect on embryonic development may be observed (see for example Özkan et al., 2009, who used white fluorescent light; and Rozenboim et al., 2004, Shafey and Al-Mohsen, 2002, and Shafey, 2004, who used monochromatic green light). In nature, a brooding hen will leave the nest intermittently, exposing her eggs to light (Archer and Mench, 2014). Although an eggshell absorbs about 99.8% of the light reaching its surface (Shafey et al., 2002), some light is able to penetrate the egg and can be perceived by the em-bryo through its light-sensitive pineal gland (which is located directly under the skull) (Skwarło-Sońta, 1996) as well as through its developing eyes; the establishment of retinal vision is thought to be completely mature by E19 (Mey and Thanos, 2000).
Previous studies have shown that by providing a chicken embryo with light during in-cubation, compared with dark inin-cubation, various aspects of the chicken’s life are affec-ted, such as embryonic brain development (reviewed by Tzschentke, 2012), post hatch fear behaviour (full spectrum fluorescent light; Archer and Mench, 2014), pectoralis muscle growth (green light, Rozenboim et al., 2004; Halevy et al., 2006; Zhang et al., 2012 or fluorescent white light, Özkan et al., 2012a), and corticosterone levels (fluores-cent white light, Özkan et al., 2012b). Lighted incubation applied from set till embryonic day (E)18 or hatch can influence subsequent embryonic development: it has been shown to increase embryo weight when it was applied as a 24L (white fluorescent, Garwood et al., 1973; white incandescent, Lauber, 1975; green fluorescent, Shafey and Al-Mohsen, 2002; Shafey, 2004), 15 min L:15 min D (monochromatic green LED light, Rozenboim et al., 2004) or 18L:6D (white fluorescent, Özkan et al., 2009) lighting schedule. In-cubation time furthermore decreased by 5 to 30 hours for 24L compared to 24D (white incandescent, Siegel et al., 1969; Walter and Voitle, 1972, 1973; green fluorescent, Shafey and Al-Mohsen, 2002). This suggests that the application of a light-dark schedule and the provision of continuous light can have a stimulatory effect upon embryo
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ment when compared to dark incubation.
As demonstrated, several authors have investigated the effect of light during incubation on broiler embryo development. However, additional light sources also produce heat and this may have an influence upon the temperature the embryo experiences inside the egg.
Initially, embryonic development may be accelerated by high incubation temperatures, but when applied throughout incubation they have a retarding effect on embryo develop-ment (Van der Pol et al., 2014). This may have been the case for some authors who did not find an effect of lighted incubation on body weight at hatch (Tamimie, 1967; Walter and Voitle, 1972; Zakaria, 1989; Shafey et al., 2005; Zhang et al., 2012) but made no menti-on of measures to prevent overheating of the eggs. Other authors did take into account the difference in air temperature between lighted treatments. For example, Tamimie and Fox (1967) measured air temperature inside the incubator with and without bulbs before the start of the experiment, and Shafey (2004) performed a pilot study concluding that there were no air temperature differences between dark or lighted incubation. However, air temperature can differ greatly from the temperature an embryo experiences inside the egg. Embryo temperature can vary independently from air temperature because it is dependent upon both embryonic heat production and heat transfer from the embryo to its surroundings (Meijerhof and Van Beek, 1993). Heat transfer depends on factors such as egg characteristics, air velocity, and air temperature (Lourens et al., 2011). Internal egg temperature is a more reliable readout for embryo temperature (Rozenboim et al., 2004), but it is invasive and risks killing the embryo, eliminating its own heat production from the energy balance. Lourens et al. (2011) recommend using eggshell temperature (EST) as a non-invasive, reliable reflection of embryo temperature. In the present study, heat transferred by the LED lights was taken into account by continuously incubating at a set EST of 37.8°C for all treatments, meaning that air temperature was constantly adjusted to meet the EST requirement. A constant EST of 37.8°C is considered to be optimal, leading to the most optimal hatchability and yolk free body mass (YFBM), (Molenaar et al., 2010, 2011a).
The present study aimed to investigate the effect of light during incubation on embryonic development and post hatch growth in broiler chickens, distinguishing between males and females. An EST of 37.8°C was maintained throughout incubation to eliminate em-bryo temperature as a confounding factor. We hypothesized that a lighting schedule of 12L:12D would stimulate embryonic development more than 24L or 24D, resulting in higher chick quality at hatch and better production performance up until slaughter age.