Researchers in Turkey, led by Dr Sezen Özkan at Ege University, have investigated the effects of photoperiodic lighting (16 hours of light and eight hours of dark) programmes during incubation of chicken eggs. Their studies have been published in two papers in Poultry Science.

The first examined the effects on growth and circadian physiological traits of embryos and early stress response of broiler chickens (Özkan et al., 2012a), while the second looked at the effects on early post-hatching growth, blood physiology and production performance in broiler chickens in relation to post-hatching lighting programmes (Özkan et al., 2012b). Dr Özkan's co-authors included others from Ege University as well as Yüzüncü Yil University in Van and Dokuz Eylül University in Izmir.

Photoperiodic Lighting and Adaptation to the Post-hatch Environment

The first paper (Özkan et al., 2012a) reports a study was conducted to evaluate the effect of a 16L:8D photoperiod during incubation, either during the whole incubation period (Inc0-21) or the last week of incubation (Inc14-21) on embryo growth, incubation performance and light:dark rhythm of plasma melatonin and corticosterone in relation to early stress responses of newly hatched chicks to the post-hatching environment. A dark incubation condition (IncDark) served as control.

Three batches of eggs (n=1,080, 1,320, 720) from Ross 308 broiler breeders were used in the experiment. Embryos from Inc0–21d presented a daily rhythm of melatonin at internal pipping and hatching but IncDark embryos did not.

The Inc14–21 group had rhythmic plasma melatonin at hatching only. A L:D rhythm of corticosterone was apparent at hatching. A significant incubation × sampling time interaction suggested that a lower increment in blood corticosterone level in Inc0–21 at eight hours post-hatching (light period) - as compared with hatching (dark period) values - might be associated with probable changes in the hypothalamic-pituitary-adrenal axis in Inc0–21 through incubation lighting.

This finding may also suggest improved adaptation to the post-hatching environment, according to Özkan and co-authors. Incubation lighting did not consistently affect brain malondialdehyde concentration; the only difference between groups was higher concentrations at hatching in Inc14–21, whereas incubation groups at the internal pipping stage had similar values.

Mean relative asymmetry (RA) did not differ with incubation lighting.

The malondialdehyde and RA results indicate that neither lighting nor darkness during the overall incubation exacerbated embryo oxidative and developmental stress.

An increased breast muscle weight was observed at hatching only in Inc14–21. The Inc0–21 group had heavier embryo weights relative to egg weight and decreased residual yolk but had no effect on chick weight, relative heart and liver (as a percentage of embryo weight), hatchability, embryo mortality, incubation time, oxidative stress or mean RA.

From these results, Özkan and co-authors concluded that their results provide further evidence that photoperiodic lighting during incubation (Inc0–21) may improve adaptation of chicks to a novel environment at hatching, possibly giving birds a better start for early post-hatching development.

Photoperiodic Lighting and Effects on Post-Hatch Performance

Photoperiodic incubation lighting might improve bird adaptation to a novel environment at hatching for a better start in early post-hatching development, hypothesised Özkan and co-authors in the second paper (Özkan et al., 2012b).

Again, they evaluated the effect of 16L:8D lighting for either the whole incubation period (Inc0–21) or the last week of incubation (Inc14–21) but this time, they focused on early post-hatching growth, blood melatonin and corticosterone at day six as well as malondialdehyde levels in brain tissue, relative asymmetry and overall broiler performance as an interaction with the post-hatching lighting programmes. Again, dark incubation conditions (IncDark) served as control.

There were three incubation batches in the experiment. Chicks from two of three batches were reared either at 16L:8D or under continuous lighting (24 hours) for the first six days after hatching. Batch 3 chicks were reared to 35 days of age under either 16L:8D or 23L:1D.

The researchers' main finding was a significant incubation × post-hatching lighting interaction for 35-day bodyweight in broilers. Although groups had similar bodyweight under continuous lighting, Inc0–21 and Inc14–21 broilers were, respectively, 94g and 78g heavier than IncDark birds under 16L:8D at 35 days.

Lighted incubation groups increased gain to six days of age and increased breast muscle weights at the same time-point with no effect on other traits measured.

Post-hatching 16L:8D reduced the gain and day-6 breast muscle.

Significant incubation × post-hatching lighting and post-hatching lighting × sampling time interactions for blood melatonin may indicate that Inc0–21 affects melatonin diurnal rhythms even at six days of age under continuous light.

Lower blood corticosterone levels at six days of age in Inc0–21 chicks reared under 16L:8D post-hatching may support the hypothesis that incubation lighting can modify the bird stress response, probably affecting the hypothalamic-pituitary-adrenal axis during ontogeny, and may improve adaptation to a similar environment post-hatching.

The lower malondialdehyde concentration in brain tissue of Inc0–21 birds on day 6 may indicate lower lipid peroxidation and thus lower oxidative stress compared with IncDark.

These results provide further evidence that Inc0–21 may improve both bird adaptation to a similar photoperiodic environment and growth, probably through early entrainment of circadian physiology.

References

Özkan S., S. Yalçin, E. Babacanoglu, H. Kozanoglu, F. Karadas and S. Uysal. 2012a. Photoperiodic lighting (16 hours of light:8 hours of dark) programs during incubation: 1. Effects on growth and circadian physiological traits of embryos and early stress response of broiler chickens. Poult. Sci. 91(11):2912-2921. doi: 10.3382/ps.2012-02426

Özkan S., S. Yalçin, E. Babacanoglu, S. Uysal, F. Karadas and H. Kozanoglu. 2012b. Photoperiodic lighting (16 hours of light:8 hours of dark) programs during incubation: 2. Effects on early posthatching growth, blood physiology, and production performance in broiler chickens in relation to posthatching lighting programs. Poult. Sci. 91(11):2922-2930. doi: 10.3382/ps.2012-02427 http://ps.fass.org/content/91/11/2922.abstract

Further Reading You can view the first paper by clicking here, and the second paper clicking here. A fee may be payable in each case.

January 2013