Artificial Photoperiod Research Articles

Exposure to a winter photoperiod to produce large Atlantic salmon smolts (Salmo salar) increases energetic costs and reduces hypoxia tolerance during seawater transfer

A goal of salmon aquaculture is to produce larger, physiologically robust smolts to improve performance at time of seawater transfer and reduce time spent in marine net pens. However, little is known about whether standard processes to induce smoltification provide benefits in the production of large smolts. In Atlantic salmon (Salmo salar) reared under continuous light (24 L:0D) we applied an artificial photoperiod treatment (8 weeks of 12 L:12D followed by 4 weeks of 24 L:0D before seawater transfer) at three sizes to produce fish of ∼150–200 g, ∼400–600 g, and ∼ 1200–1300 g at seawater transfer. We then measured O2 consumption (a proxy for metabolic rate) of photoperiod treated and control salmon (kept in constant 24 L:0D until time of seawater transfer) at three time points (in freshwater prior to seawater entry, 24 h after seawater entry, and 1 month after seawater entry) to assess impacts of photoperiod treatment and seawater transfer on performance. Consistent with known higher metabolic rates in smolts vs parr, photoperiod treatment (12 L:12D) increased minimum O2 consumption (ṀO2min) by ∼13% across all three sizes and at all time points measured. Increased ṀO2min was not solely a result of increased growth rates and was associated with lower hypoxia tolerance at time of seawater transfer in ∼500 g and ∼ 1200 g salmon. Transfer to seawater reduced maximum O2 consumption (ṀO2max) acutely in ∼200 g and ∼ 500 g salmon regardless of the photoperiod treatment (12 L:12D or 24 L:0D), consistent with potential ion and osmotic disturbances leading to an osmo-respiratory compromise 24 h after seawater transfer. For both sizes of ∼200 g and ∼ 500 g, ṀO2max recovered to freshwater levels 1 month after seawater transfer. In contrast, ∼1200 g salmon showed no significant changes in ṀO2max following seawater transfer. Overall, we showed little benefits of traditional photoperiod treatments (12 L:12D) on performance of large salmon following seawater transfer. In fact, photoperiod treatment (12 L:12D) may lead to negative impacts on large salmon by increasing ṀO2min and sensitivity to environmental stress such as hypoxia. Our results, combined with other recent studies, suggest that traditional photoperiod manipulations may be unnecessary for the development of larger Atlantic salmon smolts. However, further research is needed to fully understand impacts of photoperiod manipulations on physiological performance of larger salmon at time of seawater transfer.

The dynamic landscape of chromatin accessibility and active regulatory elements in the mediobasal hypothalamus influences the seasonal activation of the reproductive axis in the male quail under long light exposure

BackgroundIn cold and temperate zones, seasonal reproduction plays a crucial role in the survival and reproductive success of species. The photoperiod influences reproductive processes in seasonal breeders through the hypothalamic-pituitary-gonadal (HPG) axis, in which the mediobasal hypothalamus (MBH) serves as the central region responsible for transmitting light information to the endocrine system. However, the cis-regulatory elements and the transcriptional activation mechanisms related to seasonal activation of the reproductive axis in MBH remain largely unclear. In this study, an artificial photoperiod program was used to induce the HPG axis activation in male quails, and we compared changes in chromatin accessibility changes during the seasonal activation of the HPG axis.ResultsAlterations in chromatin accessibility occurred in the mediobasal hypothalamus (MBH) and stabilized at LD7 during the activation of the HPG axis. Most open chromatin regions (OCRs) are enriched mainly in introns and distal intergenic regions. The differentially accessible regions (DARs) showed enrichment of binding motifs of the RFX, NKX, and MEF family of transcription factors that gained-loss accessibility under long-day conditions, while the binding motifs of the nuclear receptor (NR) superfamily and BZIP family gained-open accessibility. Retinoic acid signaling and GTPase-mediated signal transduction are involved in adaptation to long days and maintenance of the HPG axis activation. According to our footprint analysis, three clock-output genes (TEF, DBP, and HLF) and the THRA were the first responders to long days in LD3. THRB, NR3C2, AR, and NR3C1 are the key players associated with the initiation and maintenance of the activation of the HPG axis, which appeared at LD7 and tended to be stable under long-day conditions. By integrating chromatin and the transcriptome, three genes (DIO2, SLC16A2, and PDE6H) involved in thyroid hormone signaling showed differential chromatin accessibility and expression levels during the seasonal activation of the HPG axis. TRPA1, a target of THRB identified by DAP-seq, was sensitive to photoactivation and exhibited differential expression levels between short- and long-day conditions.ConclusionOur data suggest that trans effects were the main factors affecting gene expression during the seasonal activation of the HPG axis. This study could lead to further research on the seasonal reproductive behavior of birds, particularly the role of MBH in controlling seasonal reproductive behavior.

Effects of Photoperiod on Survival, Growth, Physiological, and Biochemical Indices of Redclaw Crayfish (Cherax quadricarinatus) Juveniles

Through a 30-day experiment, this study investigated the effects of five photoperiods (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) on the survival, enzyme activity, body color, and growth-related gene expression of redclaw crayfish (Cherax quadricarinatus) juveniles. The results showed that C. quadricarinatus juveniles under 18L:6D and 24L:0D photoperiods exhibited the highest survival rate, which was significantly higher than the survival rates of juveniles under the other three photoperiods (p < 0.05). However, the 0L:24D group had the highest final body weight and weight gain rate, significantly surpassing those of the 12L:12D, 18L:6D, and 24L:0D groups (p < 0.05). Regarding enzyme activity and hormone levels, juveniles under the 18L:6D photoperiod exhibited relatively higher activity of superoxide dismutase (SOD), acid phosphatase (ACP), and lysozyme (LZM) enzymes than those under other photoperiods, but their levels of melatonin and cortisol were relatively low. In addition, the 24L:0D group showed the highest malondialdehyde (MDA) content. Analysis of gene expression levels revealed that retinoid X receptor (RXR) and α-amylase (α-AMY) genes in C. quadricarinatus juveniles exhibited significantly higher expression levels under the 18L:6D photoperiod than those under the other four photoperiods (p < 0.05). With increasing daylight exposure, the body color of C. quadricarinatus changed from pale blue to yellow–brown. In summary, C. quadricarinatus juveniles achieved high survival rates, good growth performance, strong antioxidant stress response, and immune defense capabilities under an 18 h photoperiod. Therefore, in the industrial seedling cultivation of redclaw crayfish, it is recommended to provide 18 h of daily light. Further, the study demonstrated the ability to manipulate the body color of C. quadricarinatus through controlled artificial photoperiods. These findings provide essential technical parameters needed for the industrial cultivation of C. quadricarinatus juveniles.

Differential responses to artificial photoperiods of the rising and falling phases of human melatonin rhythm are consistent with a dual oscillator hypothesis.

Circadian rhythms and sleep-wake cycles were measured in volunteers staying singly in temporal isolation unit where they were exposed to artificial short and long light-dark (LD) cycles for 7 days. The long day consisted of 16-h light and 8-h dark (LD 16:8) and the short day consisted of 8-h light and 16-h dark (LD 8:16). During the light period, bright light of approximately 5,000 lux was given from the ceiling and during the dark period there was no illumination. Sleep was monitored by bed sensors, wrist actiwatch, and polysomnography (PSG) on the first and last nights of the schedule. Sleep length was significantly longer under LD 8:16 than under LD 16:8 and the sleep quality estimated by PSG was worse under LD 8:16 than under LD 16:8, which were comparable to natural seasonality in sleep. The circadian rhythm in plasma melatonin was measured in dim light (10 lux) before and after the LD exposures. The nocturnal melatonin secretion (NMS) was significantly longer after LD 8:16 than after LD 16:8 due to differential phase shifts of the rising and falling phases of NMS. After LD 8:16, the falling phase was much advanced than the rising phase, whereas after LD 16:8 the rising phase was much delayed than the falling phase, resulting in the NMS compression. These results indicate that the light sensitivity in terms of phase shifting is different in the two circadian phases, supporting a dual oscillator hypothesis with different phase-response curves for light in the human circadian system.NEW & NOTEWORTHY The present study demonstrated differential light responsiveness of the rising and falling phases of nocturnal melatonin secretion in human subjects exposed to artificial long (LD 16:8) and short days (LD 8:16) and suggested the involvement of different oscillators under these phases. The findings well mimicked the seasonality of the circadian rhythms in nature and consisted with the evening/morning dual oscillator hypothesis proposed originally for nocturnal rodents, providing a new concept for the human circadian system.

Effects of artificial photoperiods on antigen-dependent immune responses in rainbow trout (Oncorhynchus mykiss).

In this study, we investigated the effects of the artificial photoperiods that mimic summer (16L:8D; 16 h Light: 8 h Dark) and winter (8L:16D) solstices, equinoxes (12L:12D), and the artificial 24-h light regimen (24L:0D) on the leukocyte populations and the T helper and regulatory type responses on rainbow trout (Oncorhynchus mykiss). Using flow cytometry analysis, we found that photoperiod induces changes in head kidney leukocyte subsets. The lymphoid subset increased in the 16L:8D summer solstice regime. The analysis using antibodies against B and T cells showed the increase of CD4-1+ T lymphocytes and other unidentified lymphoid cells, with no changes in the B cells. To investigate the modulatory influence of the photoperiod on the fish T cell response, we quantified in the head kidney the transcript levels of genes involved in the Th1 type response (t-bet, ifn-ƴ, il-12p35, il-12p40c), Th2 type response (gata3, il-4/13a), Th17 response (ror-ƴt, il-17a/f), T regulatory response (foxp3α, il-10a, tgf-β1), and the T cell growth factor il-2. The results showed that the seasonal photoperiod alone has a limited influence on the expression of these genes, as the only difference was observed in il-14/13a and il-10a transcripts of fish kept on the 16L:8D regimen. In addition, the 24L:0D treatment used in aquaculture produces a reduction of il-14/13a and il-17a/f. We also evaluated the effect of photoperiod in the presence of an antigenic stimulus. Thus, in fish immunized with the recombinant viral protein 1 (rVP1) of infectious pancreatic necrosis virus (IPNV), the photoperiod had a striking influence on the type of adaptive immune response. Each photoperiod fosters a unique immune signature of antigenic response. A classical type 1 response is observed in fish subjected to the 16L:8D photoperiod. In contrast, fish in the 12L:12D photoperiod showed only the upregulation of il-12p40c. Furthermore, none of the cytokines were increased in fish maintained on the artificial 24L:0D regimen, and a decrease in the master transcription factors (t-bet, ror-ƴt, and foxp3α) was observed. Thus, fish on the 12L:12D and 24L:0D photoperiod appear hyporesponsive regarding the T cell response. Altogether, this study showed that photoperiods modify the magnitude and quality of the T-helper response in rainbow trout and thus impact essential mechanisms for the generation of immune memory and protection against microorganisms.

Evaluation of locomotor activity in female Chelonoidis chilensis (Testudinidae, Gray 1870) in response to artificial photoperiod and temperature treatments

Abstract Turtles as many other reptiles are capable of orientating their bodies toward the sun. This conduct requires the presence of an internal biological chronometer in the organism that regulates this behavior. Thus, a description of the internal clock in these reptiles is of interest. The assessment of locomotor activity can be considered a reliable indicator of biological clock function. This study aimed to investigate the effect of different artificial photoperiod and ambient temperature schedules on total locomotor activity of female Chelonoidis chilensis and its rhythmicity. Six C. chilensis specimens were exposed to different artificial photoperiods and temperature regimes each fixed for seven days. It was observed that the activity period during the different experimental schedules was close to the 24 hours indicating a daily rhythmicity. Moreover, all tortoises showed a similar total locomotor activity pattern displaying the most of motion during light phase. Under the condition of constant light tortoises exhibited a self-sustaining rhythm not entrained to light and temperature zeitgebers, thus, suggesting its possible endogenous periodicity. Though this study deepens the knowledge on the rhythmic system of C. chilensis, further investigations are needed to achieve a more detailed understanding of tortoise biological clock.

Revisiting TSHβ's Role in Avian Seasonal Reproduction, Insights, and Challenges from Mammalian Models.

The core neuroendocrine pathways regulating seasonal reproduction in vertebrates were characterized over a decade ago. This has led to the development of a "consensus" model of seasonal reproduction that appears to be largely conserved across mammals, birds, amphibians, reptile and fish. This model centers around the photoinduced increase in TSHβ expression in the pars tuberalis of the anterior pituitary gland as the key transducer of photic information from sensory cells to the critical switch in hypothalamic deiodinase enzyme expression that drives changes in localized thyroid hormone signaling. These changes in localized thyroid hormone signaling in the medial basal hypothalamus ultimately activate the reproductive axis. This model has in turn, been consistently supported by studies in a variety of taxa. As such, it has become the standard against which subsequent work is compared, particularly in the non-mammalian literature. However, as new studies move away from the handful of canonical model systems and begin to explore the effects of naturalistic rather than artificial photoperiod manipulations, a more nuanced picture has begun to emerge. Yet, progress in elucidating the detailed events of reproductive photostimulation has been uneven across the research community. In this perspective, I draw on emerging data from studies in free living animals that challenges some of the established assumptions of the avian consensus model of reproduction. Specifically, the role of TSHβ and its dissociation from deiodinase signaling. I then discuss how these apparently surprising findings can be contextualized within the context of the mammalian seasonal literature. In turn, this ability to contextualize from the mammalian literature highlights the breadth of the current gap versus our understanding of the molecular neuroendocrine mechanisms of seasonality in mammals versus birds and other non-mammalian seasonal breeders.

EN LOS CABRITOS MACHOS DE REGIONES SUBTROPICALES, LA EXPOSICIÓN A DÍAS LARGOS ARTIFICIALES ESTIMULA UNA MAYOR TASA CRECIMIENTO, UN MEJOR DESARROLLO E INCREMENTA LA GLUCEMIA

<p><strong>Background.</strong> Small ruminants from subtropical regions are sensitive to respond physiologically to natural photoperiodic changes. In some subtropical goat production systems as located in semi-arid areas of México, the main objective is to obtain in the shortest possible time, males with a suitable weight and body development for sale. <strong>Objective.</strong> The present study determines if the exposure to artificial long day photoperiod could promote a growth rate, body development and an increased glycemia in male goat kids compared with those under natural short days. <strong>Methodology.</strong> Starting on late September, 21 creole male goat kids (13 ± 0.1 week aged; mean ± SEM) were assigned to one of the two experimental groups. In the natural short days group, males remain under natural short days from autumn-winter (GDC, n = 10). In the artificial long days group, males were exposed to artificial photoperiod consisting in 16 h light and 8 h darkness (GDL, n = 11). The study lasted until the animals had 35 weeks of age. All animals were fed according their nutritional requirements. <strong>Results.</strong> During the study, the body weight of the GDL animals was higher than that of the GDCN males (P < 0.05). Due to this, the daily weight gain (GDP) obtained at 23 weeks of age was higher in the GDL males (165 g/day) than that registered in the GDC males (143 g/day; P <0.05). In some periods, the males of the GDL had higher body mass index (IMC) than the males of the GDC (P < 0.05). Thoracic perimeter at week 32 was greater in the GDL males than in the GDC males (P <0.05). The height at the withers did not reach significant differences in the comparisons between groups in the different weeks measured (P > 0.05). However, the total height at the withers gained during the study was significantly higher in the GDL males than in the GDC males (P < 0.01). Under fasting conditions, GDL males had higher levels (P < 0.05) of blood glucose in some periods than GDC males. <strong>Implications.</strong> The present study demonstrate that artificial long days stimulates growth in goats as occurs in other ruminants<strong>. Conclusion.</strong> Exposure of the male goat kids from subtropical regions to artificial long days, promotes a higher growth rate, better body development and increased glycemia compared to kids maintained under natural short-day photoperiods.</p>

Daylength Shapes Entrainment Patterns to Artificial Photoperiods in a Subterranean Rodent.

Photoperiodism plays an important role in the synchronization of seasonal phenomena in various organisms. In mammals, photoperiod encoding is mediated by differential entrainment of the circadian system. The limits of daily light entrainment and photoperiodic time measurement can be verified in organisms that inhabit extreme photic environments, such as the subterranean. In this experimental study, we evaluated entrainment of circadian wheel-running rhythms in South American subterranean rodents, the Anillaco tuco-tucos (Ctenomys aff. knighti), exposed to different artificial photoperiods, from extremely long to extremely short photophases (LD 21:3, LD 18:6, LD 15:9, LD 9:15, LD 6:18 and LD 3:21). Artificial photoperiods synchronized their activity/rest rhythms and clear differences occurred in (a) phase angles of entrainment relative to the LD cycle and (b) duration of the daily activity phase α. These photoperiod-dependent patterns of entrainment were similar to those reported for epigeous species. Release into constant darkness conditions revealed aftereffects of entrainment to different photoperiods, observed in α but not in the free-running period τ. We also verified if animals coming from summer and winter natural photoperiods entrained equally to the artificial photoperiods by evaluating their phase angle of entrainment, α and τ aftereffects. To this end, experimental animals were divided into "Matching" and "Mismatching" groups, based on whether the experimental photoperiod (short-day [L < 12 h] or long-day [L > 12 h]) matched or not the natural photoperiod to which they had been previously exposed. No significant differences were found in the phase angle of entrainment, α and τ aftereffects in each artificial photoperiod. Our results indicate that the circadian clocks of tuco-tucos are capable of photoperiodic time measurement despite their natural subterranean habits and that the final entrainment patterns achieved by the circadian clock do not depend on the photoperiodic history.

The High Testosterone Concentrations of the Bucks Used in the "Male Effect" Is Not a Prerequisite for Obtaining High Ovarian Activity in Goats from Mediterranean Latitudes.

Simple SummaryThe introduction of males to anovulatory females previously separated from males (or even without separation) can induce estrous activity within a few days; this is termed the “male effect”. It is a common reproductive management practice on the extensive and semi-extensive goat farms of the Mediterranean area. High testosterone concentrations at the moment of the induction of the “male effect” are usually considered essential to obtain a high reproductive response from female goats. By controlling the secretion of GnRH, it is possible to control the gonadotropins and testosterone secretion. GnRH agonists have been used to control testosterone concentration in different species. Two experiments were carried out to determine if the contact during the seasonal anestrous of the males with the females modifies the testosterone concentrations and if the use of a GnRH agonist on the bucks to avoid variation in testosterone concentrations when the male effect is induced causes variation in the reproductive response of the does.Two experiments were carried out. Firstly, 54 anestrous females were placed in contact with photostimulated males (Photo; n = 27) or with no photostimulated males (Natural; n = 27). Moreover, a group of bucks treated with artificial photoperiod and a group of bucks subjected to natural photoperiod without contact with females was used (Photo Isolated and Natural Isolated, respectively). In the Natural groups, the testosterone concentrations were similar except for three days after the introduction of the bucks to the does (19.72 ± 4.11 vs. 2.05 ± 0.25 ng/mL for Natural and Natural isolated bucks, respectively, p < 0.05). However, no differences were observed in the Photo groups during the entire experiment. The percentage of females showing estrous was higher in the group of females in contact with photostimulated bucks (96 vs. 74%, respectively, p < 0.05). In the second experiment, a GnRH agonist, deslorelin, was used to regulate the testosterone concentrations of the bucks. Seventy anestrous females were divided into five groups depending on the treatment received by the bucks to which they were exposed: photostimulated bucks (Photo group, n = 14); photostimulated bucks but treated with the agonist at the onset of the photoperiod treatment (Photo-Ago Long group, n = 13); photostimulated bucks but treated with the agonist at the end of the photoperiod treatment (Photo-Ago Short group, n = 15); bucks receiving no photostimulation but treated with the agonist at the end of the photoperiod treatment period (Natural-Ago Short group, n = 13) and bucks receiving no photostimulation nor agonist (Natural group, n = 15). The agonist treatment increased testosterone concentrations after the injection, which remained high for the entire experiment (p < 0.05). Six days after the introduction of the bucks to the does, the testosterone concentrations increased only in the Natural group reaching similar concentrations to the other groups (12.17 ± 6.55, 16.69 ± 4.53, 8.70 ± 0.61, 11.03 ± 1.45 and 14.42 ± 3.64 ng/mL for Photo, Photo-Ago Long, Photo-Ago Short, Natural-Ago Short and Natural bucks, respectively, p > 0.05). No differences in reproductive parameters were observed (p > 0.05). These results demonstrate that, at Mediterranean latitudes, anestrous females can stimulate the testosterone concentrations of bucks after a period of isolation. The high testosterone concentrations are not a prerequisite for an adequate response to the male effect.

Effects of Continuous Light (LD24:0) Modulate the Expression of Lysozyme, Mucin and Peripheral Blood Cells in Rainbow Trout

Continuous photoperiod is extensively used in fish farming, to regulate the reproductive cycle, despite evidence suggesting that artificial photoperiods can act as a stressor and impair the immune system. We evaluated the potential effects of an artificial photoperiod on mucus components: lysozyme and mucin, in juvenile rainbow trout (Oncorhynchus mykiss) after exposure for one month to natural photoperiod (LD12:12) or constant light (LD24:0) artificial photoperiod. For each treatment, we assessed changes in peripheral blood cells (erythrocytes and leukocytes) and skin mucus component concentrations. Our results show a decrease in lysozyme concentration, while mucin levels are increased. Similarly, we find elevated monocytes and polymorphonuclears under constant light photoperiod. These findings suggest that LD24:0 regulates lysozyme, mucin, and leukocytes, implying that artificial photoperiods could be a stressful.

Effect of Photoperiod with Sunlight at Thermal Stress and Sperm Parameters in Guinea Pigs.

&lt;b&gt;Background and Objective:&lt;/b&gt; Photoperiod can regulate reproductive physiological processes in mammals, in which improvements in testosterone concentration, testicular volume and seminal quality have been reported. The aim was to evaluate the influence of photoperiod treatments on guinea pigs' spermatic parameters. &lt;b&gt;Materials and Methods:&lt;/b&gt; Thirty guinea pigs, between males and females, were distributed in two rooms with the photoperiodic treatment of 10 hrs light and 14 hrs dark (PT&lt;sub&gt;1&lt;/sub&gt; with artificial photoperiod and PT&lt;sub&gt;2&lt;/sub&gt; photoperiod with sunlight by opening windows from 08:00-18:00) and one without any direct light stimulus (PT&lt;sub&gt;0&lt;/sub&gt;) for 78 days. The temperature and humidity were recorded and the TH index was calculated for each room. The sperms were recovered in Tris base medium from the epididymis of 16 males to determine sperm concentration, motility, kinetic parameters, vitality, HOST, acrosomal integrity and DNA fragmentation. &lt;b&gt;Results:&lt;/b&gt; Sperm values in PT&lt;sub&gt;1&lt;/sub&gt; and PT&lt;sub&gt;0&lt;/sub&gt; were similar but PT&lt;sub&gt;2&lt;/sub&gt; obtained values lower in sperm concentration, non-progressive motility, total motility, VCL, ALH, vitality, HOST+, acrosomal integrity, sperm with non-fragmented DNA and no pregnancies were reported (0/5). A 100% pregnancy was observed in PT&lt;sub&gt;0&lt;/sub&gt; (4/4) and 50% in PT&lt;sub&gt;1&lt;/sub&gt; (2/4). However, precocity was evidenced in PT&lt;sub&gt;1&lt;/sub&gt; compared to PT&lt;sub&gt;0&lt;/sub&gt;. PT&lt;sub&gt;2&lt;/sub&gt; recorded higher peaks in temperature (33.8°C, THI 81, considered as thermal stress) compared to PT&lt;sub&gt;0&lt;/sub&gt; (32.65°C, THI 81.8) and PT&lt;sub&gt;1&lt;/sub&gt; (32.75°C, THI 81.6). &lt;b&gt;Conclusion:&lt;/b&gt; An artificial photoperiod can improve sperm characteristics and reproductive precociousness of guinea pigs, unlike the photoperiod with sunlight, which generated low spermiogram values and absence of pregnancy due to thermal stress.

Pekin duck productivity, physiological stress, immune response and behavior under 20L:4D and 16L:8D photoperiods

As duck production becomes more prevalent on a global scale, modern duck housing systems must utilize artificial lighting photoperiods to maximize production and welfare; however, limited research has examined the manipulation of photoperiods on Pekin ducks. The objective of this study was therefore to determine the effects of two photoperiods – 20 h of light (L): 4 h of darkness (D) and 16 L:8D - on the growth, stress, and fear responses of 384 Pekin ducks during the grow-out period. The 20L:4D ducks had a more efficient feed conversion ratio (P < 0.02). The 20L:4D ducks were less stressed, as indicated by reduced plasma corticosterone concentration, heterophil to lymphocyte ratio, and composite asymmetry score (P < 0.02), and elevated humoral immune response to a Newcastle Disease Virus vaccine (P = 0.035) compared to 16L:8D ducks. These results indicated ducks reared under the 20L:4D photoperiod had more efficient nutrient metabolism and stronger humoral immune response to a Newcastle Disease Virus vaccine due to improved FCR and decreased stress and the effects of stress compared to the 16L:8D photoperiod group. Fear response data from this study was considered inconclusive, and future investigation is still required to elucidate how various photoperiod schedules influence the fear response of Pekin ducks. The results of this study emphasize the need for appropriate, species-specific artificial photoperiods in modern grow-out facilities to maximize the production of Pekin ducks while also reducing stress.

Effects of artificial photoperiod on the body colouration in the ornamental fish poecilia sphenops

In Orange balloon Molly, Poecilia sphenops, the development of chronic stress due to continuous exposure to artificial LED lighting irrespective to photoperiod causes deterioration in the body colour even in the presence of carotenoid rich green water and artificial feed with added additives in the experimental fishtank setup. In the present study, the effects of continuous exposure to lighting and its consecutive development of chronic stress causes the body colouration to fade off in the freshwater ornamental live bearer, Poecilia sphenops, though the fishes were provided with colour enhancing as well as stress relievingfactors. Several trials showed that, whatever may be the colour enhancing agents provided, artificial lighting for long exposure irrelevant to the normal photoperiod remains as a strong anti-colouration as well as stress inducing factor and remains unaffected to any antagonistic factors. To conclude photoperiod is an essentialfactor to be concerned for colour enhancement in Poecilia sphenops.

Reproductive management of the transitional mare

The mare is a seasonally polyoestrous long-day breeder with a physiological breeding season lasting from April–October in the Northern Hemisphere. The hypothalamic-pituitary-gonadal axis in the mare is subject to a circannual endogenous rhythm that is primarily regulated by day length. Increasing ambient photoperiod in the spring alters the pattern of melatonin secretion. The resulting stimulation of hypothalamic gonadotropin-releasing hormone secretion triggers pituitary follicular stimulating hormone release and follicular growth. Exposure of mares in deep anoestrus to a stimulatory photoperiod remains the most successful method of advancing the first ovulation of the season. The most commonly used lighting regimen is providing a fixed length of 15–16 hours of light exposure and 8–9 hours of dark, with a minimum light intensity in a stable of 100-lux (100–200 watt incandescent bulb). Other methods include using an additional 2.5 hours of light beginning at sunset and a pulse lighting system, providing 1 hour of light, 9.5–10.5 hours after the onset of darkness, during the photosensitive phase. Alternatively, the EquilumeTMlight masks provide a unilateral LED light source emitting 50 lux of blue-light directly to the eye during the hours after dusk (until 11 pm). Mares that have not been maintained under lights, or that have been exposed to ineffective light therapy, may require therapeutic hormonal intervention to advance the onset of the first ovulation of the season. Many hormone protocols involving progestins, GnRH, dopamine agonists and recombinant luteinising hormone/follicle stimulating hormone have been studied with variable results. Therapy is typically more effective when started either in late transitional mares or following a period of stimulatory artificial photoperiod.

Reproductive management of the transitional mare

The mare is a seasonally polyoestrous long-day breeder with a physiological breeding season lasting from April–October in the Northern Hemisphere. The hypothalamic-pituitary-gonadal axis in the mare is subject to a circannual endogenous rhythm that is primarily regulated by day length. Increasing ambient photoperiod in the spring alters the pattern of melatonin secretion. The resulting stimulation of hypothalamic gonadotropin-releasing hormone secretion triggers pituitary follicular stimulating hormone release and follicular growth. Exposure of mares in deep anoestrus to a stimulatory photoperiod remains the most successful method of advancing the first ovulation of the season. The most commonly used lighting regimen is providing a fixed length of 15–16 hours of light exposure and 8–9 hours of dark, with a minimum light intensity in a stable of 100-lux (100–200 watt incandescent bulb). Other methods include using an additional 2.5 hours of light beginning at sunset and a pulse lighting system, providing 1 hour of light, 9.5–10.5 hours after the onset of darkness, during the photosensitive phase. Alternatively, the EquilumeTM light masks provide a unilateral LED light source emitting 50 lux of blue-light directly to the eye during the hours after dusk (until 11 pm). Mares that have not been maintained under lights, or that have been exposed to ineffective light therapy, may require therapeutic hormonal intervention to advance the onset of the first ovulation of the season. Many hormone protocols involving progestins, GnRH, dopamine agonists and recombinant luteinising hormone/follicle stimulating hormone have been studied with variable results. Therapy is typically more effective when started either in late transitional mares or following a period of stimulatory artificial photoperiod.

The role of exogenous melatonin and photoperiod on productive and reproductive performance of Ossimi sheep.

To determine effect of the administration of exogenous melatonin and photoperiod on initiating the lambing season and improving reproductive efficiency of sheep, a total of thirty-four multiparous, non-pregnant Ossimi ewes aged 3-5 years with average body weight 55.94±1.80 kg were used. After weaning and the starting of the breeding season, the ewes were divided into four groups; the 1st group (7 ewes) was exposed to natural daylight (NL) and severed as a control group, the 2nd group (9 ewes) was exposed to 16-hour artificial lighting (AL), the 3rd group (10 ewes) was exposed to natural daylight+18-mg/h melatonin (NL+MEL), while the 4th group (8 ewes) was exposed to 16-hour artificial lighting+18-mg/h melatonin (AL+MEL). The treatment of the ewes continued throughout the mating season and for three consecutive estrus cycles (60 days). Ewes were weighed before mating and after parturition. Reproductive traits were recorded after parturition. Results revealed that exogenous melatonin (induced by either natural daylight or artificial photoperiod) exhibited significantly (P≤0.05) higher body weights (6.20±1.711 and 4.14±1.91kg for NL+MAL and AL+MEL groups more than the control group). Both of the melatonin treatment and the use of artificial light for 16 h insignificantly influenced reproductive parameters (percentages of fertility, conception rate, scanning, lambing rate, and fecundity rate of Ossimi ewes. Fertility and conception rates tended to be higher in (NL+MEL) and (AL+MEL) groups, while SP percentage, lambing and fecundity rates were higher in treated groups than control. The percentage of the number of services per conception (NSC) and abortion rate were insignificantly reduced in treated ewes as compared with the control. Both weaning rate and the survival rate was elevated (P≥0.05) in treated ewes than untreated ones. Lambing interval and days open were significantly lower (P≤0.05) in AL+MEL group than AL and NL+MEL groups. The lambs’ weight at birth, weaning, net gain, and average daily gain tended to be higher in (NL+MET) and (AL+MEL) groups than other groups with insignificant differences. It can be concluded that, stimulation of melatonin (induced by natural daylight and artificial photoperiod manipulation) might be a useful tool in improving reproductive performance and lamb production in Ossimi sheep.

In dual-purpose subtropical goats, 1 h of extra-light given from 16 to 17 h after dawn (pulse of light) in winter stimulates milk yield.

This research communication addresses the hypothesis that in dual-purpose goats, exposure to 1 h of extra-light given from 16 to 17 h after dawn (pulse of light) in winter stimulates milk yield. One group of goats was maintained under natural short photoperiod (natural day; ND (n = 7)). Another group of lactating females was submitted to an artificial long-day photoperiod consisting of 16 h light and 8 h darkness (long days; LD (n = 7)). A third group of females received one single hour of extra-light 16 h after the fixed dawn (pulse of light; PL (n = 6)). Goats from LD and PL yielded 30% more milk than goats from ND. Mean percentages of fat, protein and lactose contents in milk did not differ between the 3 groups at any stage of lactation, but these components in grams/day were higher in goats from PL than in the others two groups within the first 45 d of lactation. In conclusion, dual-purpose lactating goats that started their lactation during natural short days, the daily exposition to a 1-h pulse of light is sufficient to stimulate milk yield compared to females maintained under natural short photoperiod.

Biological Measurements and Hormonal Profile in Female Gilthead Sea Bream (Sparus Aurata) In Response to Human Chorionic Gonadotropin (HCG) Injection

Water temperature and photoperiod only or with HCG injection are the most important factors driving sexual maturation in fish. This study investigates the possibility of induced spawning of Gilthead Sea bream in captivity by exposing to program of water temperature and artificial photoperiod with or without HCG injection. A total number of 60 Gilthead Sea Bream were collected and kept in indoor fiber circular holding tanks filled with salt water, under controlled photoperiods and temperature. They were divided into two groups. The first group was exposed to water temperature 21.5 to 18 °C and artificial photoperiod programs (control). The second group was exposed to water temperature 21.5 to 18 °C and artificial photoperiod programs and injected with single dose of HCG. The experiment conducted for 4 months. After the end of the third and fourth months, and after 24 and 48 hours after HCG injection, K factor, gonadal weight, gonadosomatic index (GSI %), fecundity and egg diameter were measured and blood samples were collected. The Results of gonadal weight, fecundity, egg diameter, LH and progesterone levels were increased in injected group when compared to control while the results of GSI, and FSH showed significant decreased (P<0.05) when compared to control. It could be concluded that HCG injection in single dose (1000 IU/Kg BW) aiding with water temperature and artificial photoperiod programs induced increasing the maturation of gilthead sea bream in captivity.

Effect of Artificial Photoperiod Program on the Maturation Stages of Gilthead Sea Bream (Sparus Aurata)

Photoperiod is one of the most important factors driving sexual maturation in fish. This study showed the effect of artificial photoperiod program on the maturation stages of Gilthead Sea bream in captivity. A total number of 78 Gilthead Sea bream (Sparus aurata) broodstock (48 male and 30 female) of 295.56 g and 332.03 g average body weight, respectively, fishes were collected and kept in indoor fiber circular tanks filled with salt water and under controlled photoperiods. They were divided into 2 groups. The first group was exposed to water temperature 22 ± 1 C, natural photoperiod and natural light intensity (control). Fish of the second group was kept at water temperature 22 ± 1° C and exposed to artificial photoperiod program with 600 lux light intensity. The experiment was conducted for 4 months. At the end of every month Gonadosomatic Index (GSI %) and histological sections were done. Results showed that GSI value was highest in second group after the third month in female and in second month in male when compared to fish in the control group. The histological sections confirmed these results. It could be concluded that photoperiod program is an initiative for reproductive cycle and gonadal maturation but it couldn’t reach the final maturity and can induce spawning of gilthead sea bream in captivity.