Nutritional supplementation of breeding hens may promote embryonic development through the growth hormone-insulin like growth factor axis

The late stage of embryo development is a crucial period of metabolic changes, with rapid organ development requiring a substantial supply of nutrients. During this phase, maternal nutritional levels play a vital role in the growth, development, and metabolism of the offspring. In this study, we added 2 doses of β-carotene (βc) (120 mg/kg and 240 mg/kg) to the daily diet of Hailan Brown laying hens to investigate the impact of maternal nutritional enrichment on embryo development. Maternal nutrition supplementation significantly increased the expression of chicken embryo liver index, growth hormone (GH), insulin-like growth factor-1 (IGF-1), and hepatocyte growth factor (HGF) in serum. At the same time, the expression of GH/growth hormone receptor (GHR), IGF-1 mRNA, and Proliferating Cell Nuclear Antigen (PCNA) protein in the liver was upregulated, indicating that maternal nutrition intervention may promote chicken embryo liver development through the GH-IGF-1 axis. Transcriptome sequencing results showed that differential genes in liver after maternal nutritional supplementation with β-carotene were enriched in pathways related to cell proliferation and metabolism. Consequently, we postulated that maternal β-carotene supplementation might operate via the GH-IGF-1 axis to regulate the expression of genes involved in growth and development, thereby promoting liver development. These results contribute to formulating more effective poultry feeding strategies to promote offspring growth and development.

Effects of prenatal dichromatic light exposure on hatching results and post-hatch performance of Japanese quail

Present study evaluated the effect of lighted incubation on pre- and post-hatch performance of Japanese quail. In a completely randomized design, 1200 eggs were evenly divided into 4 treatments groups having six replicates (each tray was considered as replicate), 50 eggs each. Different dichromatic lights (Green + Red; GR, Green + Blue; GB, and Blue + Red; BR) of 250 lux were provided during incubation for 12 h daily and effects of these lights very evaluated on hatching results and post-hatch growth. After hatch, 600 quail chicks were divided into 4 treatments, 6 replicates, and 25 birds each. Regarding hatching traits, better hatchability was found in the GR group compared to GB, BR, and dark group; while early embryonic mortality was lower in BR, GB, and dark group than GR; mid embryonic mortality was lower in dark group and late embryonic mortality was noted in the GR group than those of other treatment groups. In addition, moisture loss during incubation was minimum in BR and dark groups; however, chick spread was better in the GR group. In terms of growth performance, weight gain was better in the GR group; feed intake in dark, feed conversion ratio in BR, and livability were better in BR and GR group. In morphometrics, keel and shank length were higher in all the colored groups (GB, BR, and GR) whereas body length, wing spread, shank circumference, drumstick length, and circumference were higher in the GR group. Regarding serum chemistry, glucose, albumin, and globulin levels were higher in the GR group. It was concluded that under the experimental conditions, GR light at the prenatal stage to Japanese quail eggs positively influenced hatching performance and post-hatch growth.

Effect of photoperiod during incubation on embryonic temperature, hatch traits and performance of two commercial broiler strains

Provision of light during incubation has shown the potential to enhance hatching traits and affect posthatch productivity, physiology, and behavior. In this study, 2 repeated trials were conducted to investigate the effect of photoperiod and strain on the embryo temperature, hatching traits and posthatch growth performance of 2 commercial strains of broilers (Ross 308 and Cobb 500). In each trial, hatching eggs were randomly distributed into 6 incubators with 3 photoperiod treatments: blue LED light for 12 h d^-1 (12L:12D) or 18 h d^-1 (18L:6D) during entire incubation were compared with no illumination condition (DARK). Data were analyzed as a 3 × 2 factorial arrangement with the trial as the blocking factor. Embryos incubated under 12L:12D and 18L:6D had lower air cell temperature (P < 0.05) than the DARK embryos from d 13 of incubation onward except on the day of candling. The response of air cell temperature to periodic illumination differed between 2 strains. Cobb embryos had lower air cell temperature in 12L:12D than those incubated with 18L:6D from d 16 of incubation onward, whereas lower air cell temperature was found in Ross embryos when illuminated with 18L:6D photoperiod compared to those under 12L:12D. The 12L:12D treatment was associated with improved (P < 0.05) navel closure condition of hatchlings. There were no differences in hatchability, embryo mortality, body weight, or length at hatch among photoperiod groups or its combination with strain. No differences in production parameters were found between DARK and illuminated groups. However, 12L:12D had heavier (P < 0.05) body weight on d 14 of age and higher (P < 0.05) body weight gain than 18L:6D from d 7 to 14 of age. The results of this study indicate that providing blue LED light up to 18 h d^-1 has no detrimental effect on production of broilers, however, 12L:12D light regime improved chick quality at hatch compared to DARK and resulted in heavier birds by d 14 compared to 18L:6D.

Monochromatic Green Light Stimulation during Incubation Alters Hepatic Glucose Metabolism That Improves Embryonic Development in Yangzhou Goose Eggs

The influence of monochromatic green light stimulation on hatching performance and embryo development has been studied in chickens, but not geese. The liver has crucial functions in the regulation of energy metabolism during embryogenesis, but its involvement in green light transduction is still unidentified. We aimed to determine the influence of monochromatic green light on Yangzhou goose hatching performance and embryo development. We also investigated the metabolomics and transcriptomic responses of the embryonic liver to green light to determine the underlying molecular mechanisms. Eggs were incubated under either 12 h of monochromatic green light/dark (12 L:12D) cycles or 24 h of darkness (0G:24D). Green light promoted embryonic development and hatching performance, also affected the expression of myogenic regulatory factors associated with muscle development. It also shortened hatching time and elevated plasma levels of growth hormone and insulin-like growth factor-1. Metabolomics and transcriptomic results revealed differentially expressed genes and metabolites with enhanced gluconeogenesis/glycolysis and increased plasma glucose and pyruvate levels under green light. Hence, the growth-promoting effect possibly through regulating energy metabolism in the liver and myogenic regulatory factors in muscle. Our findings provide important and novel insights into the mechanisms underlying the beneficial effects of green light on goose embryos.

The Role of Incubation Conditions on the Regulation of Muscle Development and Meat Quality in Poultry

Muscle is the most abundant edible tissue in table poultry, which serves as an important source of high protein for humans. Poultry myofiber originates in the early embryogenic stage, and the overall muscle fiber number is almost determined before hatching. Muscle development in the embryonic stage is critical to the posthatch muscle growth and final meat yield and quality. Incubation conditions including temperature, humidity, oxygen density, ventilation and lighting may substantially affect the number, shape and structure of the muscle fiber, which may produce long-lasting effect on the postnatal muscle growth and meat quality. Suboptimal incubation conditions can induce the onset of myopathies. Early exposure to suitable hatching conditions may modify the muscle histomorphology posthatch and the final muscle mass of the birds by regulating embryonic hormone levels and benefit the muscle cell activity. The elucidation of the muscle development at the embryonic stage would facilitate the modulation of poultry muscle quantity and meat quality. This review starts from the physical and biochemical characteristics of poultry myofiber formation, and brings together recent advances of incubation conditions on satellite cell migration, fiber development and transformation, and subsequent muscle myopathies and other meat quality defects. The underlying molecular and cellular mechanisms for the induced muscle growth and meat quality traits are also discussed. The future studies on the effects of external incubation conditions on the regulation of muscle cell proliferation and meat quality are suggested. This review may broaden our knowledge on the regulation of incubation conditions on poultry muscle development, and provide more informative decisions for hatchery in the selection of hatching parameter for pursuit of more large muscle size and superior meat quality.

Incubation Temperature and Lighting: Effect on Embryonic Development, Post-Hatch Growth, and Adaptive Response

During incubation, the content of the egg is converted into a chick. This process is controlled by incubation conditions, which must meet the requirements of the chick embryo to obtain the best chick quality and maximum hatchability. Incubation temperature and light are the two main factors influencing embryo development and post-hatch performance. Because chicken embryos are poikilothermic, embryo metabolic development relies on the incubation temperature, which influences the use of egg nutrients and embryo development. Incubation temperature ranging between 37 and 38°C (typically 37.5–37.8°C) optimizes hatchability. However, the temperature inside the egg called “embryo temperature” is not equal to the incubator air temperature. Moreover, embryo temperature is not constant, depending on the balance between embryonic heat production and heat transfer between the eggshell and its environment. Recently, many studies have been conducted on eggshell and/or incubation temperature to meet the needs of the embryo and to understand the embryonic requirements. Numerous studies have also demonstrated that cyclic increases in incubation temperature during the critical period of incubation could induce adaptive responses and increase the thermotolerance of chickens without affecting hatchability. Although the commercial incubation procedure does not have a constant lighting component, light during incubation can modify embryo development, physiology, and post-hatch behavior indicated by lowering stress responses and fearful behavior and improving spatial abilities and cognitive functions of chicken. Light-induced changes may be attributed to hemispheric lateralization and the entrainment of circadian rhythms in the embryo before the hatching. There is also evidence that light affects embryonic melatonin rhythms associated with body temperature regulation. The authors’ preliminary findings suggest that combining light and cyclic higher eggshell temperatures during incubation increases pineal aralkylamine N-acetyltransferase, which is a rate-limiting enzyme for melatonin hormone production. Therefore, combining light and thermal manipulation during the incubation could be a new approach to improve the resistance of broilers to heat stress. This review aims to provide an overview of studies investigating temperature and light manipulations to improve embryonic development, post-hatch growth, and adaptive stress response in chickens.

Light regimen on health and growth of broilers: an update review

The importance of lighting regimen is increasing with the industrialization of poultry production, as lighting has been intimately associated with not only the establishment of rhythm and synchronous physiology of broiler chickens, but also the secretion of hormones associated with broiler maturation and growth. In recent years, increasing attention has been paid to the effects of lighting management on growth performance, immune status, and welfare of broilers. An appropriate lighting regimen, including proper source of lighting, intensity, duration, and wavelength (color) of light, is crucial to improve the growth performance and welfare of broilers. In this review, we updated the impacts of different light regimens on health and growth performance of broilers.

Mel1b and Mel1c melatonin receptors mediate green light-induced secretion of growth hormone in chick adenohypophysis cells via the AC/PKA and ERK1/2 signalling pathways

A previous study showed that melatonin (MEL) membrane receptors 1b (Mel1b) and Mel1c promoted the secretion of growth hormone (GH) in chick adenohypophysis cells under monochromatic green light. However, the intracellular signalling pathways of these two receptors are unclear. Therefore, cultured adenohypophysis cells derived from chickens exposed to monochromatic green light were treated with MEL, Mel1b- and Mel1c-specific blockers, protein kinase A (PKA) inhibitors and adenylate cyclase (AC), or AC activator in vitro to explore the signal transduction mechanism that promote the secretion of GH. The results showed that Mel1b and Mel1c participate in MEL-mediated green light-induced secretion of GH in chick adenohypophysis cells. However, MEL increased cyclic adenosine monophosphate (cAMP) levels, and p-PKA protein levels were blocked by a Mel1b-specific antagonist but not a Mel1c-specific antagonist, which indicated that Mel1b affected the secretion of GH via the AC/cAMP/PKA signalling pathway. Moreover, Mel1b and Mel1c both activated ERK1/2 to regulate the secretion of GH. In addition, intracellular and extracellular Ca²⁺ channels were also involved in secretion of GH in chick adenohypophysis cells. These results demonstrate that the MEL mediated green light-induced secretion of GH in chick adenohypophysis via the Mel1b/AC/PKA/ERK1/2, Mel1c/ERK1/2, and intracellular and extracellular Ca2⁺ channel signalling pathways.

The effect of selected in ovo green light photostimulation periods on post-hatch broiler growth and somatotropic axis activity

Targeted in ovo green light (GL) photostimulation during the last days of broiler egg incubation increases embryonic expression of the somatotropic axis, similar to in ovo green light photostimulation from embryonic day (ED) 0 to the end of incubation. The aim of this study was to examine the effect of selected in ovo GL photostimulation periods on post-hatch broiler growth. Four hundred twenty fertile broiler eggs were divided into 7 treatment groups: the first incubated in the dark (standard conditions) as a negative control; the second incubated under monochromatic GL from ED0-ED20 (positive control); the third group incubated under monochromatic GL light from ED15-ED20; the fourth, fifth and sixth groups were incubated under monochromatic GL on ED16, ED17, and ED18, respectively; and the seventh group was incubated under monochromatic GL from ED18-ED20. All illumination was provided intermittently using LED lamps. After hatch, all chicks were transferred to a controlled room under standard rearing conditions. The group incubated under green light from ED18 until hatch showed similar results to the positive control group in body weights, as well as breast muscle weights (as % of body weights), and an elevation in the somatotropic axis activity during the experiment. We suggest that broiler embryos can be exposed to in ovo GL photostimulation from ED18 until hatch (hatching period), and still exhibit the same performance as obtained by photostimulation from d 0 of incubation.

Providing colored photoperiodic light stimulation during incubation: 1. Effects on embryo development and hatching performance in broiler hatching eggs

Providing lighting schedule during incubation has been shown to improve chick quality and reduce stress posthatch. This study was conducted to evaluate the effects of providing light of different colors during incubation on embryo development, air cell temperature, the spread of hatch, and hatching performance. Four batches of eggs (n = 2,176, 1,664, 1,696 and 1,600) from Ross 308 broiler breeders were used in the experiment. In each trial, eggs were randomly distributed into 4 lighting treatments. The incubation lighting treatments included: incubated under dark as control, illuminated with white, red or blue lights for 12 h daily. There were no incubation lighting treatment differences in embryo development, the spread of hatch, hatchability, embryo mortality, hatch weight, chick length, navel closure quality, yolk-free body weight, or relative spleen weight. However, embryos incubated under red light had lower average air cell temperature than those in dark, white or blue light treatments. This finding may suggest higher melatonin secretion during the scotophase when illuminated with red light. Male chicks incubated under dark had a higher bursa of Fabricius weight than males illuminated with blue light. In conclusion, these results suggest that the red, white and blue light stimulation during incubation had no negative effects on hatchability, embryo mortality, spread of hatch or day-old chick quality, but may have potential impacts on immunity and energy metabolism in broiler embryos.

Providing colored photoperiodic light stimulation during incubation: 2. Effects on early posthatch growth, immune response, and production performance in broiler chickens

Previous findings have reported that providing light during incubation can affect hatchability and chick quality. This study was conducted to investigate the effects of providing light during incubation on posthatch broiler production parameters, thermoregulation and immune response. Lights with different wavelengths were used over the course of four separate hatches. Ross 308 broiler hatching eggs were randomly distributed into 4 lighting treatments for each hatch. The incubation lighting treatments included: dark as control, white, red, or blue lights for 12 h d^-1 (200 lux at egg level). Broilers hatched from each incubator with the same gender were placed into one of 8 sets of pens (3 pens/set) and raised under 18 h d^-1 photoperiod. Six birds per pen were immunized intraocularly with AviPro ND-IB Polybanco vaccine on d 10 and 21 posthatch. Chicks hatched under white and blue lights had heavier (P < 0.05) body weight and higher (P < 0.05) feed consumption than the control group during the first 6 h postplacement. No differences in vent temperature were found among treatments at 24 h posthatch (P > 0.05). Chicks hatched with light stimulation however had more stable (P < 0.05) cloaca temperature at 36 h posthatch. No differences in average body weight gain, feed consumption or feed conversion ratio were found among lighting treatments between d 7 and d 35. On d 14 of age, birds hatched from red light had higher (P < 0.05) total IgG concentration than those hatched under dark, blue or white light. These results indicated that in ovo light stimulation with different wavelengths did not affect growth parameters of broilers at market age. Providing photoperiodic blue and white light during incubation improved the production parameters of broilers during the first week posthatch.

Effect of exposure to different light colors on embryonic development and neurophysiological traits in the chick embryo

Background and Aim:

Many environmental factors exist that influence embryonic development which is missing in the poultry industry, such as light in incubation facilities or hatcheries. Light plays an important role in the growth and development of chick embryos, whereas dark environments can lead to hatching failure or embryo distortion. Therefore, this study aimed to demonstrate the importance of light and its various colors on the growth and development of broiler chick embryos.

Materials and Methods:

Four treatments were used to study the impact of various light colors on the growth of embryos and their neurophysiological traits: Dark without light (D), red light (RL), blue light (BL), and green light (GL), with three replicates per treatment (25 eggs/replicate) for a total of 300 fertile Ross 308 eggs. Each treatment was assigned to one incubator (75 eggs/incubator), whereas all other conditions were kept the same.

Results:

The results showed a significant increase (p<0.01) in embryonic development for embryo weight, chick body weight, hatchability, and embryo index for RL, BL, and especially GL. RL, BL, and especially GL significantly increased (p<0.01) neurophysiological traits of the neurons, brain weight, and brain index.

Conclusion:

The use of light during the embryonic period affects the development of the embryo and its neurophysiological traits.

Targeted differential illumination improves reproductive traits of broiler breeder males

Artificial targeted illumination has a pivotal role in reproductive processes of poultry. The light-absorption mechanism in birds consists of 2 main components: the eye (retinal photoreceptors) and extraretinal photoreceptors located in the brain. Previous studies conducted on hens have shown that photostimulation of brain extraretinal photoreceptors elevates reproductive activity, whereas retinal photostimulation suppresses it. We tested the effect of targeted differential photostimulation (TDP) on reproductive activities of broiler breeder males. Fifty broiler breeder roosters (Ross), 21 wk of age, were divided into 5 environmentally controlled light-treatment rooms (n = 10) equipped with individual cages. Rooms 1 and 2 had 2 parallel lighting systems consisting of red light (630 nm) and green light (514 nm), and rooms 3 and 4 had parallel red and blue (456 nm) lighting systems. Room 5, illuminated with white light, served as the control. Birds of all groups were kept under short day (6L:18D) for 2 wk with both lighting systems in each treatment room turned on. At 23 wk of age, birds were photostimulated by gradually increasing one of the lighting systems to 14 h of light in each room, while the other lighting system was left on short day (6L:18D). Weekly semen samples were collected until 65 wk of age and analyzed for volume, motility, concentration and vitality. Monthly blood samples were drawn for plasma hormone assays. At 65 wk of age, roosters were euthanized and hypothalamus, pituitary gland, retina and testes samples were taken for mRNA expression analysis. TDP using long-day red light and short-day green light significantly increased reproductive performance, manifested by higher semen volume, motility and concentration, and testis weight; furthermore, this group had higher plasma testosterone levels, higher GnRH mRNA expression in the hypothalamus, lower levels of aromatase in the testes, and lower mRNA expression of hypothalamic serotonin transporter, and of pituitary prolactin and its receptors in the testes. This is the first study showing a positive effect of TDP on reproduction of broiler breeder roosters.

Effects of age at photostimulation on sexual maturity and reproductive performance in rooster breeders

The 2 × 4 factorial experiment was designed to determine the effect of strain and photostimulation age on sexual maturity and reproductive performance of rooster breeders. A total of 96 White Leghorn (WL) and 120 Beijing You Chicken (BYC) roosters were randomly allocated to 4 treatments at 14 wk of age. The treatments represent photostimulation at 16, 18, 20, and 22 wk of age, respectively (PS16, PS18, PS20, and PS22), in both strains. Photostimulation was achieved by increasing the day length from 8L:16D to 14L:10D and by increasing lighting intensity from 10 lx to 80 lx. Three birds from each interaction were sacrificed to characterize the comb and testis weights at 4 time points: 1 d before photostimulation and 2, 4, and 6 wk after photostimulation. Semen quality and hatching performance with the semen of the experimental roosters were measured at 30 and 45 wk of age, respectively. Results showed that the testis weight of PS20 and PS22 in WL and BYC was 6.4- and 2.9-fold higher than that of PS18 before photostimulation, while testis weight of PS18 in both strains increased sharply after photostimulation. The diameter of seminiferous tubules increased in the photostimulated roosters as compared with the nonphotostimulated ones, and mature spermatozoa were produced 4 wk after photostimulation and at 20 wk of age for PS16. The WL had lower semen volume and total sperm count than BYC (P < 0.01), but there was no difference on effective sperm count (P > 0.05). In addition, semen quality traits were not affected by age at photostimulation (P > 0.05) in both strains. The fertility and hatching performance were not affected by strain or photostimulation age (P > 0.05). In summary, the sexual maturation of rooster breeders can be advanced by photostimulation at an early age, which does not lead to a difference in semen quality or hatching performance at adult stage.

Effects of green light emitting diode light during incubation and dietary organic macro and trace minerals during rearing on tibia characteristics of broiler chickens at slaughter age

This study was designed to evaluate the effects of green light emitting diode (LED) light during incubation and dietary organic macro and trace minerals during rearing on tibia morphological, biophysical, and mechanical characteristics of broiler chickens at slaughter age. The experiment was setup as a 2 × 2 × 2 factorial arrangement, with the following treatments: 1) light during incubation (green LED light or darkness), 2) macro mineral source during rearing (organic or inorganic Ca and P), and 3) trace mineral source during rearing (organic or inorganic Fe, Cu, Mn, Zn, and Se). A total of 2,400 eggs (Ross 308) were either incubated under green LED light (16L:8D) or in complete darkness. After hatch, a total of 864 male broiler chickens were reared until slaughter age (day 42) and provided with 1 of 4 diets, differing in macro and/or trace mineral source. During rearing, the experiment had a complete randomized block design with 9 replicate pens per treatment and 12 chickens per pen. At slaughter age (day 42), 2 chickens per replicate were randomly selected and tibia bones were obtained. Tibia weight, length, thickness, osseous volume, pore volume, total volume, mineral content, mineral density, ultimate strength, and stiffness were determined. Green LED light during incubation did not affect any of the tibia characteristics. Dietary organic macro minerals positively affected most of the tibia morphological, biophysical, and mechanical characteristics compared to the inorganic macro minerals, whereas trace mineral sources did not affect tibia characteristics. It can be concluded that dietary organic macro minerals Ca and P stimulated tibia characteristics, whereas green LED light during incubation and dietary trace minerals during rearing did not affect tibia characteristics, locomotion, or leg disorders.

In ovo green light photostimulation during the late incubation stage affects somatotropic axis activity

Targeted green light photostimulation during the last stage of broiler incubation increases expression of the somatotropic axis. The purpose of this study was to further shorten the in ovo green light photostimulation and determine the critical age for photostimulation in broilers embryos, as a future strategy for broiler incubation. Fertile broilers eggs (n = 420) were divided into 5 treatment groups. The first group was incubated under standard conditions (in the dark) as the negative control group. The second was incubated under intermittent monochromatic green light using light-emitting diode lamps with an intensity of 0.1 W/m² at shell level from embryonic day (ED) 0 of incubation until hatch, as a positive control. The third, fourth, and fifth groups were incubated under intermittent monochromatic green light from ED 15, 16, and 18 of incubation, respectively, until hatch. All treatment groups showed elevated somatotropic axis expression compared with the negative control, with the group incubated under monochromatic green light from ED 18 until hatch showing results closest to the positive control. This suggests that broiler embryos can be exposed to in ovo green light photostimulation from a late stage of incubation (when transferring the eggs to the hatchery) and exhibit essentially the same outcome as obtained by photostimulation during the entire incubation period.

Mel1c Mediated Monochromatic Light-Stimulated IGF-I Synthesis through the Intracellular Gαq/PKC/ERK Signaling Pathway

Previous studies have demonstrated that monochromatic light affects plasma melatonin (MEL) levels, which in turn regulates hepatic insulin-like growth factor I (IGF-I) secretion via the Mel1c receptor. However, the intracellular signaling pathway initiated by Mel1c remains unclear. In this study, newly hatched broilers, including intact, sham operation, and pinealectomy groups, were exposed to either white (WL), red (RL), green (GL), or blue (BL) light for 14 days. Experiments in vivo showed that GL significantly promoted plasma MEL formation, which was accompanied by an increase in the MEL receptor, Mel1c, as well as phosphorylated extracellular regulated protein kinases (p-ERK1/2), and IGF-I expression in the liver, compared to the other light-treated groups. In contrast, this GL stimulation was attenuated by pinealectomy. Exogenous MEL elevated the hepatocellular IGF-I level, which is consistent with increases in cyclic adenosine monophosphate (cAMP), G_αq, phosphorylated protein kinase C (p-PKC), and p-ERK1/2 expression. However, the Mel1c selective antagonist prazosin suppressed the MEL-induced expression of IGF-I, G_αq, p-PKC, and p-ERK1/2, while the cAMP concentration was barely affected. In addition, pretreatment with Ym254890 (a G_αq inhibitor), Go9863 (a PKC inhibitor), and PD98059 (an ERK1/2 inhibitor) markedly attenuated MEL-stimulated IGF-I expression and p-ERK1/2 activity. These results indicate that Mel1c mediates monochromatic GL-stimulated IGF-I synthesis through intracellular G_αq/PKC/ERK signaling.

In-ovo green light photostimulation during different embryonic stages affect somatotropic axis

Previous studies demonstrated that in-ovo photostimulation with monochromatic green light increased the somatotropic axis expression in broilers embryos. The objective of the current study was to detect the critical period for in-ovo GL photostimulation, in order to find the optimal targeted photostimulation period during the incubation process. Three hundred thirty-six fertile broiler eggs were divided into 4 groups. The first group was incubated under dark conditions as a negative control. The second incubated under intermittent monochromatic green light using light-emitting diode (LED) lamps with an intensity of 0.1 W\m2 at shell level from d 0 of the incubation as a positive control. The third group incubated under intermittent monochromatic green light from d 10 of the incubation. The last group incubated under intermittent monochromatic green light from d 15 of the incubation. In-ovo green light photostimulation from embryonic d 0 (ED0) increased plasma growth hormone (GH), as well as hypothalamic growth hormone releasing hormone (GHRH) and liver growth hormone receptor (GHR) and insulin-like growth factor-1 (IGF-1) mRNA levels. In-ovo green light photostimulation from ED10 increased the GH plasma levels compared to the negative control group, without affecting somatotropic axis mRNA genes expressions of GHRH, GHR, and IGF-1. In-ovo green light photostimulation from ED15 caused an increase in both the plasma GH levels and the somatotropic axis mRNA genes expressions of GHRH, GHR, and IGF-1, compared to the negative control group. These results suggest that the critical period of somatotropic axis acceleration by GL photostimulation start at 15 d of incubation.