Targeted differential photostimulation alters reproductive activities of domestic birds.

Modern poultry production systems use environmentally controlled houses providing only artificial illumination. The role of light in reproduction of poultry depends on light quality (photoperiod, intensity/brightness, and spectrum), which enables us to provide custom-made illumination, targeted for the elevation of reproductive activities. Artificial targeted illumination significantly affects poultry reproduction. This phenomenon is based on the mechanism of light absorption in birds, which consists of two main components: the eye (retinal photoreceptors) and brain extraretinal photoreceptors. Several experiments on turkey hens and broiler breeder males and females have shown that photostimulation of brain extraretinal photoreceptors, while maintaining retinal photoreceptors under non-photostimulatory conditions, elevates reproductive activity by increasing egg production of hens and semen quality of roosters. In addition, we found acceleration in all gonadal axis parameters, leading to the acceleration in the production rate. Furthermore, we studied the role of retinal activation in gonadal axis suppuration and identified the role of serotonin in this phenomenon. As for today, several broiler breeder farms use targeted illumination based on our studies with excellent results.

Role of the serotonergic axis in the reproductive failure associated with aging broiler breeder roosters.

Reproductive failure associated with aging is a well-known phenomenon. However, the mechanism by which this failure occurs in broiler breeder roosters is still unclear. A previous study conducted in our laboratory, comparing young and aging broiler breeder roosters, demonstrated an elevation in hypothalamic vasoactive intestinal peptide (VIP) and pituitary prolactin (PRL) gene expression accompanied by a deterioration of gonadal axis function. This resulted in a decrease in semen-quality variables as roosters aged. The objective of this study was to examine the involvement of the serotonergic axis in the age-associated reproductive failure in broiler breeder roosters. Cobb roosters aged 64 wk were divided into 3 groups (n = 20 each): parachlorophenylalanine (PCPA) administration, active immunization against chicken VIP, and controls. At 69 wk of age, each group was divided into 2 equal subgroups: 1 received ovine PRL and the other served as controls. Weekly semen volume, concentration and motility, and plasma testosterone, estradiol, and PRL concentrations were examined. At the end of the experiment, roosters were euthanized, testes were weighed, and hypothalamus and pituitary were removed to assay the expression of genes encoding hypothalamic GnRH-I, pituitary FSH, pituitary LH, hypothalamic VIP, and pituitary PRL. Both PCPA administration and active immunization against chicken VIP significantly increased testis weight, semen volume, sperm concentration, ejaculation grade, plasma testosterone level, and GnRH-I, FSH and LH gene expression compared with controls (P ≤ 0.05). In addition, a decrease in plasma estradiol and PRL concentrations and VIP and PRL gene expression was observed in PCPA- and VIP-immunized birds compared with controls (P ≤ 0.05). Administration of PRL in all groups decreased gonadal axis function and semen-quality variables (P ≤ 0.05). Collectively, these results suggest that the increasing expression levels of the serotonergic axis in aging broiler breeder roosters inhibit proper gonadal function and reproductive performance. This article establishes for the first time the inhibitory role of serotonin on reproduction in aging roosters.

Age-related changes in gonadal and serotonergic axes of broiler breeder roosters.

Fertility of domestic roosters decreases at ≈ 50 wk of age. In a previous study on aging white leghorn roosters, low fertility was accompanied by low levels of both hypothalamic vasoactive intestinal peptide (VIP) and pituitary prolactin (PRL) mRNA expression; however, their role in aging broiler breeder rooster reproduction is still unclear. In this study we compared reproductive activities of young (35-wk-old) and aging (73-wk-old) broiler breeder roosters. Weekly semen volume; concentration and ejaculation grade; and concentrations of plasma testosterone, estradiol, and PRL were examined. Every other week, 10 roosters from each group were euthanized, their testes weighed, and hypothalamus and pituitary removed to determine mRNA expression of hypothalamic GnRH-I, pituitary FSH, pituitary LH, hypothalamic VIP, and pituitary PRL. Aging roosters had significantly lower testis weight and semen volume, sperm concentration, ejaculation grade and plasma testosterone and low hypothalamic GnRH-I, pituitary FSH, and pituitary LH mRNA expression than young roosters (P ≤ 0.05). Aging roosters had higher concentrations of plasma estradiol and PRL and higher hypothalamic VIP and pituitary PRL mRNA expression than young roosters (P ≤ 0.05). We suggest that PRL, which is known to inhibit the gonadal axis, and its releasing factor, VIP, play an important role in the reproductive failure associated with age in broiler breeder roosters.

The effect of active immunization against vasoactive intestinal peptide (VIP) and inhibin on reproductive performance of aging White Leghorn roosters.

Decreasing fertility in aging domestic roosters is a well-known phenomenon. Aging is manifested by a decrease in plasma testosterone level, testis function, and spermatogenesis, resulting in a low level of fertility. The roles of vasoactive intestinal peptide (VIP) and testicular inhibin in this aging process are not clear. The effects of active immunization against VIP, inhibin, or the combination of both hormones on the reproduction of aging White Leghorn (WL) roosters were assayed. In experiment 1a, 60 White Leghorn roosters (67 wk of age) were divided into 4 groups (n = 15/group). The first group was actively immunized against VIP, the second against inhibin, the third against VIP and inhibin, and the fourth served as a control. Active immunization against VIP decreased semen quality parameters, plasma steroid levels, and gene expression of gonadotropin-releasing hormone-I (GnRH-I), follicle-stimulating hormone (FSH), luteinizing hormone (LH), LH receptor, VIP, and prolactin (Prl). Immunization against inhibin increased some of the semen quality parameters and FSH mRNA gene expression but decreased inhibin gene expression. In experiment 1b, at 94 wk of age, we took the actively immunized against VIP group and the control group and divided them into 2 subgroups (n = 7 or 8): the first group was injected with 1 mg of ovine Prl (oPrl) daily for 7 d, and the second group served as a control. Administration of oPrl to previously VIP-immunized birds significantly elevated semen quality parameters. We suggest that VIP, Prl, and inhibin have an important effect on the reproductive axis in aging roosters. Active immunization against VIP-depressed reproductive activity and Prl administration restored their reproduction, indicating that both VIP and Prl are essential for reproduction in aging roosters. Immunization against inhibin improved FSH mRNA gene expression, suggesting a negative role of inhibin on FSH secretion in aging roosters. Not all semen quality parameters increased significantly after immunization against inhibin, even though FSH mRNA gene expression increased, suggesting interference in testicular function in aging roosters.

The effect of active immunization against vasoactive intestinal peptide and inhibin on reproductive performance of young White Leghorn roosters.

The neuropeptides vasoactive intestinal peptide (VIP) and gonadal inhibin have long been considered putative regulators of reproduction in hens. However, their role in young roosters remains unclear. We studied the effect of active immunization against VIP, inhibin, and a combination of both hormones on reproduction in young White Leghorn roosters. At 13 wk of age, White Leghorn roosters (n = 60) were split into 4 groups (n = 15). One group was actively immunized against VIP, the second against inhibin, the third against both VIP and inhibin, and the fourth, untreated, served as a control. Active immunization against VIP enhanced reproductive parameters as manifested by increased semen quality, plasma steroid levels, and mRNA gene expression of hypothalamic gonadotropin-releasing hormone-I, pituitary follicle-stimulating hormone, pituitary luteinizing hormone (LH), and decreased mRNA gene expression of hypothalamic VIP, pituitary prolactin, and testicular LH receptor. In contrast, immunization against inhibin decreased reproductive parameters such as semen quality, plasma steroid levels, mRNA gene expression of pituitary follicle-stimulating hormone and testicular inhibin. The combined treatment showed the greatest increase in semen quality parameters, plasma steroid levels, and mRNA gene expression of hypothalamic gonadotropin-releasing hormone-I, pituitary follicle-stimulating hormone, pituitary LH, and testicular LH receptor. Moreover, it significantly reduced mRNA gene expression of hypothalamic VIP and pituitary prolactin and mildly reduced that of testicular inhibin. These results suggest that VIP plays a negative role, at a young age, in reproduction of roosters that is similar to that in hens and that inhibin is as important in reproductive function in young roosters as in mammals.

The role of retinal and extra-retinal photostimulation in reproductive activity in broiler breeder hens.

Photostimulation of retinal photoreceptors, which are sensitive to green light, appears to inhibit reproductive activity in birds, whereas photostimulation of extra-retinal photoreceptors, which are sensitive to red light, accelerates it. The objective of this study was to determine the effect of either retinal or extra-retinal photostimulation on reproductive activities of broiler breeder hens. At 23 wk of age, Cobb hens (N=135) were divided into 9 rooms with individual cages (n=15). At 24 wk of age, 3 rooms were photostimulated (14L:10D) with white light (Control, n=45). Six rooms had 2 parallel lighting systems, red (660 nm) and green (560 nm), which were both on during 6 out of 14 h of the light period. Then, in 3 of these rooms, the green light was turned off and hens were exposed to a total of 14 h of red light (Red, n=45), and in the other 3, the red light was turned off and green lighting continued for a total of 14 h (Green, n=45). The Green group had reduced egg production; reduced plasma concentrations of ovarian steroids; reduced luteinizing hormone (LH)-beta, vasoactive intestinal peptide (VIP), and prolactin mRNA expression; and greater retinal green opsin mRNA expression (P < or = 0.05). The Red group had greater egg production; greater gonadotropin-releasing hormone-I (GnRH-I) and red opsin gene expression in the hypothalamus; and lesser green opsin gene expression in the retina (P < or = 0.05). We suggest that selective photostimulation of extra-retinal photostimulation as opposed to retinal photostimulation is a key factor in the determination of successful reproduction of broiler breeder hens.

Monochromatic light stimuli during embryogenesis enhance embryo development and posthatch growth.

Photostimulation with green light accelerated BW and muscle development of broilers. In experiment 1, temperature sensors were inserted into 50 broiler eggs. The eggs were placed under 5 green light-emitting diode (LED) lamps at an intensity of 0.1 W/m2 at eggshell level for 5, 10, 15, 20, and 25 min (n = 10). Egg temperatures were recorded continuously. A high correlation was found between lighting period and egg temperature elevation, and an intermittent light regimen of 15 min on and 15 min off was found to eliminate light-induced egg overheating. In experiment 2, the effect of in ovo green light photostimulation on embryonic development was studied. Five hundred fertile eggs were divided into 2 groups: the first was photostimulated with green light from 5 d of incubation until hatch (0.1 W/m2 intensity) and the second was incubated in the dark. In ovo green light photostimulation caused a significant elevation in BW and breast muscle weight during embryo development and posthatch until 6 d of age. In experiment 3, 240 fertile broiler eggs were divided into 2 groups as described in experiment 2. At hatch, chicks from each in ovo light treatment were divided into 2 subgroups: the first was reared under green light and the second under white light. In ovo photostimulation with green light enhanced BW and breast muscle weight. However, rearing under green light did not have any synergistic effect on BW. Collectively, the results suggest that stimulation with green light enhances development and growth in chicks and that the best effect is achieved when this stimulus is provided during incubation.