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Growth rate and feed efficiency during the pullet phase as well as reproductive status during the laying phase are 2 of the main parameters underlying the performance of commercial laying hens; each of these can be influenced by artificial lighting. Once pullets are ready for sexual maturation, increased photoperiod stimulates the release of GnRH-I, while reducing the expression of GnIH, and the HPG axis is activated. Currently, the effect of lighting spectra on production performance has been a topic of great interest for both growth in broilers and egg production in layers. Furthermore, exposure of broiler breeders and layers to green light has been suggested to have an inhibitory effect on reproductive performance by stimulating retinal photoreceptors. On the other hand, longer wavelengths, such as red (660 nm) light, have been reported to stimulate sexual maturation. However, most studies on the impact of light spectrum in layers focused on adult hens and egg production, while limited research has been conducted on the rearing of commercial layer pullets. Thus, this study investigated whether 60% red LED (light emitting diode) light or 60% green LED light (hereinafter RL and GL, respectively) during the rearing phase has the ability to impact pullet growth and sexual maturation, and whether it will result in any carry-over effect on the production performance of adult hens later in life.
A total of 14,500 Lohmann Brown-Lite day-old chicks were housed in 2 light isolated sections. Experimental lights were either RL (640 to 660 nm) or GL (515 to 525 nm). RL was used to investigate whether the rate of sexual maturation could be enhanced, whereas GL was used to investigate any effect on pullet growth during the rearing phase and whether it may result in delayed sexual maturation. Hens were kept in the adult barn until 70 woa, with feed and water provided ad libitum according to NRC requirements. Body weights were recorded weekly during the rearing phase (from 8 to 18 woa) on 50 randomly selected pullets per quadrant (n = 2 sections per treatment; n = 50 birds per section). After transfer to the adult barn, BW was recorded weekly until 30 woa and biweekly thereafter on 50 randomly selected birds per treatment. Egg production was recorded daily. During flock health care checks, BW records, blood samples, and carcasses of 10 individuals per treatment were obtained at 7, 11, 18, 25, 41 and 69 woa. From the carcasses, the left ovary and right femur were collected for further analysis, and relative weights of liver and ovary (without F1 to F6) were calculated.
A significant interaction between age and treatment on BW (P < 0.001) was observed; however, individual significant difference was observed only at 18 woa between light treatments, when pullets exposed to RL (1.57 kg ± 0.01) were heavier than GL (1.52 kg ± 0.01). Interestingly, the significant difference observed at 18 woa was at the time of transfer to the adult barn, and this may be attributed to an earlier sexual maturation of pullets reared under RL as the egg production at 19 and 20 woa of birds exposed to RL was observed to be 5 and 15% greater than birds exposed to GL, respectively. Following sexual maturity and throughout the laying period, BW was dependent on age (P < 0.001). Following transfer into the adult barn, hens from the RL treatment appeared to enter lay sooner than hens from GL, with production of 10.7% vs. 5.0% at 19 woa and 48.7% compared to 33.3% at 20 woa, for the RL and GL treatments, respectively. By the end of the production cycle, hens originating from the RL rearing treatment laid approximately 3 more eggs per hen compared to birds from GL on a hen-housed basis. No differences in relative liver or ovary weights, plasma levels of E2, bone density, cross-sectional area, or mineral content of the femur total content, trabecular space, and cortical tissues were observed between light treatments.
Spectrum lighting during the rearing period did not affect growth in layer pullets; however, rearing pullets under RL possibly accelerated sexual maturation as observed from higher egg production rate and heavier BW at initiation of lay. No carry-over effect of LED light treatments was observed from rearing to the active laying stage on the production performance of hens. The higher than expected production performance observed during the mid-lay cycle may require an advancement in the timing of calcium and vitamin D supplementation to synchronize calcium with E2 profiles and reduce the occurrence of cracked eggs and possible calcium deficiency.