Initiating egg production in turkey breeder hens: thyroid hormone involvement.

The role of thyroid hormones in the expression of photosensitivity-photorefractoriness in female turkeys was investigated through the use of an antithyroidal agent, 6-n-propyl-2-thiouracil (PTU). In experiment 1, females held continuously from hatch on long day lengths (16L:8D; LD) and fed 0.1% PTU from 0 to 16 wk, began laying eggs at 26 wk of age, peaking at 75% hen-day egg production by 29 wk, whereas controls initiated lay 3 wk earlier but only achieved less than 50% hen-day egg production. In experiment 2, PTU treatment from 10 to 18 wk severely suppressed plasma triiodothyronine and thyroxine, as confirmed by RIA. Egg production of PTU and control hens held on LD from hatch began by 23 wk, with PTU hens reaching a substantially greater rate of lay than controls. Eggs were smaller initially in both treatments but exceeded 75 g by 28 wk. In experiment 3, recycled hens on short day lengths (8L:16D) received PTU for 2 wk before LD and 12 wk thereafter; a subset of these hens was killed after 48 h of LD for immunohistochemical analysis of fos-related antigen (FRA) expression in the tuberal hypothalamus as a marker of photoinduced neuronal activity. The PTU treatment completely forestalled egg production until its withdrawal; egg production then rose sharply to control levels before resuming, along with controls, a typical seasonal decline. The PTU treatment did not impair photoinduced FRA expression. Together, these results demonstrate the following: 1) that a period of pharmacological suppression of triiodothyronine and thyroxine can substitute for short day exposure in conferring photosensitivity on juvenile-aged turkeys (and is actually superior to short day exposure), 2) that reproductive development does not limit egg production of turkey hens photostimulated as young as approximately 20 wk of age, and 3) that effects of thyroid suppression on photostimulation lie downstream of photoinduced FRA expression. Taken together, these results suggest that there is ample physiological potential to substantially advance the age of photoinduced egg production in commercial flocks.

Initiation of egg production by turkey breeder hens: sexual maturation and age at lighting.

Experiments were completed addressing photo-responsiveness in juvenile Large White turkey breeder hens, the age at sexual maturity, and the earliest age at photostimulation for egg production using conventional lighting management. In the first experiment, hens were photostimulated at 8 or 16 wk of age with a daily photoperiod of 16L:8D after receiving 8L:16D from hatch. Controls received 16L:8D continuously from hatch. In experiment 2, hens were given naturally declining long day lengths from hatch to 14 wk of age, a daily photoperiod of 8L:16D for the next 10 wk, and were then photostimulated at 24 wk of age with a daily photoperiod of 16L:8D. Data were collected by pen for the onset and rate of egg production, BW, and egg weight. The hens reached sexual maturity and laid eggs as early as 21 to 22 wk of age and the weight for the first 7 eggs was 56.1 g +/- 1.5. The hens were not photoresponsive to photoinduced egg production at 16 wk of age but were fully responsive by 24 wk of age as compared with controls. Photostimulation at 24 wk of age resulted in a slight delay in onset of lay (4 to 5 d) but otherwise typical egg production. These hens produced 113.3 eggs per hen to 54 wk of age as compared with 95.2 eggs for controls photostimulated at the more conventional 30 wk of age. Egg weight was 73.0 versus 80.0 g for the first 7 eggs laid for hens photostimulated at 24 wk of age versus 30 wk of age. At 36 wk of age, egg weights were similar (84.0 vs. 83.7 g). We may conclude that Large White turkey breeder hens can become sexually mature and lay eggs as early as about 22 wk of age. Appropriate pre-lay short day exposure is required to fully photosensitize juvenile hens for photoinduced egg production and this requires a development time beyond 16 wk of age. Photostimulation of fully photosensitive hens for a typical production period can occur as early as 24 wk of age. We demonstrated that the conventional age at lighting of 29 to 30 wk of age can be significantly advanced.

Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens.

In addition to inducing egg production, exposure to long days concomitantly activates processes that eventually result in photorefractoriness (PR) and cessation of egg production. Experiments were conducted to evaluate the duration of exposure to long days that result in these processes. In each of 3 experiments, we subjected Large White turkey breeder hens to long days (16 or 18 h per day) for differing lengths of time from initial photostimulation and then returned them to a photoperiod (12L:12D) that provided sufficient, but decreased, photoperiodic drive to support egg production but not induce PR. Photoresponsiveness was then evaluated by egg production after a return to a longer day length (20 h per day) late in the lay period and beyond the mean onset of PR typical for these turkey hens. Hens that have undergone any reduction in photoresponsiveness should not increase egg production in response to the increased photoperiod. From experiments 1 and 2, exposure to long days for as little as 1 d and as much as 9 wk from initial photostimulation did not result in an alteration in subsequent photoresponsiveness. This was based on an increased egg production response to a change in photoperiod from 12L:12D to 20L:4D after 20 wk of photostimulation that was similar to controls held continuously on 12L:12D and opposite to the response of controls held continuously on 18L:6D. It was clear that PR had been fully programmed by 20 wk of exposure to long days. Exposure to long days for 12 wk (experiment 3) resulted in a partial alteration of subsequent photoresponsiveness. It was concluded that programming of PR during late spring-summer season occurs after 9 wk of long day exposure, is not fully expressed by 12 wk of long days, and can be fully expressed by 20 wk of photostimulation.

Photostimulated expression of type 2 iodothyronine deiodinase mRNA is greatly attenuated in the rostral tuberal hypothalamus of the photorefractory turkey hen.

For many temperate-zone avian species, termination of breeding occurs when individuals no longer respond to previously stimulatory day lengths, a condition called photorefractoriness. Long day lengths induce significantly greater expression of c-fos and fos-related antigens (FRAs) in the tuberal hypothalamus of the photosensitive hen than that of the photorefractory hen. The tuber is also a site of photoinducible glial expression of type 2 iodothyronine deiodinase (Dio2), which converts thyroxine into its active form, triiodothyronine (T3). T3 induces withdrawal of glial processes from gonadotrophin-releasing hormone (GnRH) I nerve terminals, which is believed to permit the efficient release of GnRH I into the associated portal vasculature. Using a riboprobe, we tested whether long days induce Dio2 mRNA expression in the turkey tuber and, if so, whether this expression is reduced in photorefractory hens. Long days significantly induced rostral and caudal tuberal hypothalamic Dio2 expression in photosensitive hens. Photorefractory hens had reduced expression of Dio2 with most subjects expressing no detectable mRNA in the rostral tuber and variably attenuated amounts throughout the medial and caudal tuber. We also performed double-label immunohistochemistry to identify co-localisation between FRAs and glial fibrillary acidic protein, a glial marker. FRAs were present in the nuclei of a few astrocytes in the median eminence and infundibular nucleus of the tuber. The temporal and spatial coincidence between FRA and Dio2 expression, their mutual association with glia, and the attenuation of their response during photorefractoriness suggests that the two events are linked and that photorefractoriness involves a reduced capacity for photo-inducible gene expression within glia of the tuberal hypothalamus.

Diurnal variation in the cellular and humoral immune responses of Japanese quail: role of melatonin.

Experiments were conducted to determine if diurnal variations occur in the cellular and humoral immune responses of sexually mature, male Japanese quail and if this diurnal variation is mediated by the daily rhythm of melatonin. In Experiment 1, quail were exposed to LD 12:12 light-dark cycles and immune responses were measured in response to a single antigenic challenge given to different groups every 4h over a 24h period. Diurnal changes occurred in both the cellular and humoral immune responses. The cellular response was higher during the light phase than during the dark phase whereas the opposite was true for the humoral immune response. Experiment 2 was designed to determine if melatonin mediated these diurnal immune responses. Quail were maintained in continuous light (LL) to suppress endogenous melatonin production and half of them were given melatonin in the drinking water for 12h each day for 2 weeks. Contrary to control quail, significant daily variations occurred in both the humoral and cellular immune responses of birds given melatonin. As in Experiment 1, the cellular and humoral immune responses were out of phase with one another, with the humoral response being maximal when melatonin was present. We may conclude that there exists a melatonin dependent diurnal variation in both cellular and humoral immune responses of quail. The responses were inverse to one another during the daily light-dark cycle with the cellular response being maximal during the daily light period and the humoral response being maximal during the daily dark period.

Lighting for summer egg production by turkeys: day length and light intensity.

This experiment tested the hypothesis that typical poor egg production during the summer is a consequence of insufficient lighting and reduced photoperiodic drive. Large White turkey breeder hens were photostimulated at 30 wk of age with incandescent light on May 12 for summer (off-season) egg production and continued for 28 wk. The lighting treatments were given in a 2 x 2 factorial arrangement with day length and light intensity as main effects. Day lengths used were 15L:9D and 18L:6D, whereas the intensities were 567 +/- 67 and 22 +/- 2 lx. All the treatments were within a light-controlled building, and there were 8 replicate pens of 4 hens for each treatment. Data were collected, by pen, for onset and the rate of lay; BW and feed consumption at 4-wk intervals; and egg weight (EW) at 4-wk intervals including the weight of the first 14 eggs laid, livability, and plasma thyroid hormones for 8 wk postlighting. The rate of egg production through 28 wk of photostimulation was better in the hens receiving 18 than 15 h of light per day (14 eggs/hen difference) but was similar between the 2 intensity treatments. The lower number of eggs in the 15-h group was associated with a greater number of photorefractory hens than in the 18 h of light per day group (39 vs. 14%, respectively). Egg weights were similar between the 18 and 15 h of light/day treatment groups but was significantly greater in the low intensity treatment as compared with the high intensity treatment. We may conclude that by increasing photoperiodic drive by increased day length, but not light intensity, there results an improved summer egg production by turkeys and reduced incidence of photorefractoriness. Egg weight was best at a reduced light intensity.

Potential role of thyroid hormones and prolactin in the programming of photorefractoriness in turkey hens.

The domestic turkey hen is a seasonal breeder, requiring a period of short days to establish photosensitivity and a long day length to initiate egg production. The reproductive season is then limited by the onset of photorefractoriness (PR), which causes a decline, and then termination, of egg laying. In passerine birds, PR is programmed early in the reproductive season by the presence of thyroid hormones and a long photoperiod. High circulating prolactin (PRL) is thought to hasten the onset of PR. In a prior study, we reported that hens destined to have PR exhibited lower levels of thyroxine (T4) and PRL at certain points (weeks) following photostimulation than did hens destined to remain photosensitive (PS), a result opposite to what might be expected. The present study was conducted to further explore the possible relationship between circulating hormone levels and subsequent PR in the commercial turkey hen at times (days) closer to photostimulation than our previous study. Plasma levels of triiodothyronine (T3), T4, and PRL were compared in 2 subpopulations of hens identified retrospectively after 50 wk of egg production: A group of 17 hens that exhibited PR (mean onset = 27 wk of photostimulation) and a group of "good" layers that remained PS (mean production = 210 eggs/50 wk). Results showed no differences between groups in plasma T3 or T4 levels or in the T3:T4 ratio at -6, 0, 1, 3, and 7 d from photostimulation. Plasma PRL levels were significantly higher at 8 and 9 wk after photostimulation in hens that remained PS vs. those that became PR. We conclude that thyroid hormone levels around the time of photostimulation either are not actively related to programming of subsequent PR in turkeys or programming for PR in the turkey hen occurs later in the reproductive cycle than in passerine birds. We further conclude that hens that exhibit PR tend to have lower circulating PRL levels early in the reproductive season than hens that remain PS and lay at a relatively high rate.

Spontaneous recovery of photosensitivity by turkey breeder hens given prolonged exposure to long day lengths.

Three experiments were done to examine spontaneous photosensitivity (SP) and the associated renewal of egg production in Large White turkey breeder hens. In experiment 1, hens were photostimulated with 16 h of light:8 h of dark in December for 54 wk. In experiment 2, SP was examined in a different season than experiment 1. One group of hens was recycled and then photostimulated with 16 h of light:8 h of dark for 23wk. Another group of hens was not recycled and received 16 h of light:8 h of dark throughout the experiment. Egg production was used to assess SP in both experiments 1 and 2. Experiment 3 was designed to produce SP and renewed egg production during prolonged exposure (64 wk) to constant, long day lengths and to evaluate circulating thyroid hormones immediately prior to the renewal of egg production. Egg production was recorded daily to assess SP, and blood samples were taken weekly for radioimmunoassay for thyroid hormones. In both experiments 1 and 2, there was SP and renewed egg production, and this occurred in the fall season. Egg production increased gradually from less than 5% to a peak of 67% (experiment 1) and 38% (experiment 2) in November. In experiment 3, SP occurred in the fall, and egg production increased gradually and was similar to control hens from 8 wk of lay to the end of the experiment. Both groups also had similar declines in egg production following a decrease in photoperiod at wk 24 of the experiment. In the 8-wk period preceding the onset of laying, there were no significant differences between control and SP hens in plasma thyroid hormone levels. In both groups, there was a significant time effect for plasma triiodothyronine, expressed as a parabolic pattern of change. It was concluded that for turkey hens maintained in prolonged and constant long day lengths that SP and renewal of egg production occurs in the fall season. This response was independent of season of photostimulation, did not alter photoresponsiveness to shorten day lengths, and was preceded by a parabolic increase in plasma triiodothyronine.

Enhancement of cellular and humoral immunity following embryonic exposure to melatonin in turkeys (Meleagris gallopavo).

Two experiments were performed to determine the effect of in ovo melatonin supplementation on the ontogeny of immunity in the Large White turkey poult. Different levels of melatonin were injected into the air cell of the egg 4 days prior to hatch. In Experiment 1, turkey embryos received 3 ml of solution containing 200, 100, 50, 25, 10, or 1 microg/ml of melatonin. The hatchability at each dose was determined and compared to vehicle-injected controls. In Experiment 2, only poults from melatonin treatments in Experiment 1 that resulted in normal hatchability (10 and 1 microg/ml) were used. Lymphoproliferative responses to phytohemagglutinin (PHA-P) and primary antibody responses to Chukar red blood cells (CRBC) were determine at five time intervals: 0, 1, 7, 14, and 21 days post-hatch. At each of these times, including 28 days post-hatch, treatment effects on body weights were determined. At 28 days post-hatch, bursal, thymic, and splenic weights were obtained. In ovo melatonin administration significantly accelerated (P0.05) the development of cell-mediated (PHA-P) and humoral (CRBC) immune responses, and these responses were significantly elevated above vehicle-injected controls through 21 days post-hatch. No effect was observed on bursal, thymic, splenic or body weights. These data suggest that embryonic exposure to melatonin enhances post-hatch immune development and responsiveness.

Thyroid hormone and prolactin profiles in male and female turkeys following photostimulation.

The turkey hen, a photosensitive bird, will become photorefractory (PR) during the reproductive cycle and will cease laying despite a stimulatory day length. This response is thought to be "programmed" by hormonal events early in the reproductive cycle. The turkey tom, in contrast, produces semen for extended periods and has not been shown to exhibit PR. We compared hormone profiles following photostimulation of hens and toms to assess differences that might program one, but not the other, for PR. We photostimulated with 16 h light per day and measured plasma prolactin (PRL), thyroxine (T4), and triiodothyronine (T3) weekly for 12 wk, and again at 16 and 22 wk. Hens were fed ad libitum, and toms were moderately feed-restricted. Results showed increasing PRL levels following photostimulation in hens, with peak levels occurring at about the time of peak egg production, and declining thereafter. Toms maintained significantly lower concentrations of PRL (P < 0.0001) than hens after 2 wk of photostimulation. A highly significant sex by time interaction in plasma T3 levels was observed due to extreme fluctuations in males. Similar, often reciprocal, fluctuations in mean T4 concentrations also occurred in males. We recycled the toms and repeated blood collections under identical conditions, but with ad libitum feeding to determine if feed restriction may have produced these unusual results. This study revealed an initial significant decline in plasma T3 levels and an increase in T4 levels immediately following photostimulation, and then steady (T4) or slowly rising (T3) levels through 12 wk photostimulation. We conclude that PRL profiles of toms and hens differ markedly during the reproductive cycle, lending support to the suggestion that rising PRL may mediate the onset of PR. Further study is needed to determine if the low plasma T3 levels in males may be related to delayed PR. The extreme fluctuations in plasma T3 and T4 levels of toms receiving relatively mild feed restriction suggest a need for further study of the metabolic effects of feed restriction in turkeys.

Effect of a single short-term reduction in photoperiod on photorefractoriness in turkey hens.

In a prior study, we reported that a high proportion of hens in a winter-laying flock became relatively photorefractory (rPR) early in the reproductive cyand that successive short-term reductions in photoperiod in such hens each initially depressed egg production but then caused a rebound in rate of lay to briefly exceed that of hens that did not exhibit rPR. The present study was conducted to assess rPR in a summer-laying flock and to determine whether a single short-term reduction in day length early in the reproductive cycle might enhance egg production and delay the onset of absolute photorefractoriness (aPR). Control hens received a photoperiod of 16L:8D throughout the experiment. Experimental hens were photostimulated with 16L:8D, received a reduced (but still stimulatory) photoperiod of 11.5L:12.5D for 2 wk beginning 8 wk after photostimulation, and then were returned to 16L:8D for the remainder of the 23-wk test period. Results showed that a single 2-wk reduction in day length shortly after the hens reached peak egg production did not significantly reduce overall flock egg production, but it also did not improve late-season egg production or retard the onset or incidence of aPR. The incidence of rPR was substantially less in this study than we had observed with a winter-laying flock (32.9 vs. 67.1%), but similar proportions of treated hens exhibited the most severe rPR response (a brief but complete cessation of egg production) in both studies (21.1 vs. 24.0%), and all treated hens that subsequently became aPR had shown this severe rPR response to the test photoperiod. We concluded that a core proportion of hens (approximately one-fifth) exhibited a strong rPR response when presented with a reduced photoperiod early in the reproductive cycle, regardless of season of the year, and that such hens were more likely to subsequently exhibit poor egg production or become aPR than flockmates that did not exhibit rPR. Therefore, some indication of the incidence of rPR early in the lay period may have a predictive value for the overall egg production of the flock.

Photostimulated fos-like immunoreactivity in tuberal hypothalamus of photosensitive vs. photorefractory turkey hens.

Photorefractoriness in commercial turkey hens can be viewed as a failure of previously sexually stimulatory photoperiods to maintain egg production via activation of cGnRH I neurons, but the neural locus of photorefractoriness, i.e., where in the brain failure occurs, is not known. We used a c-fos antiserum that detects c-Fos and Fos-related antigens to characterize Fos-like immunoreactivity (FLI) as a measure of neuronal activation. FLI was measured in somatically mature, photosensitive hens (held on short photoperiods [8L:16D] for at least 10 weeks) before (non-photostimulated-photosensitive group) and after 48 h of exposure to long photoperiods (16L:8D; photostimulated-photosensitive group). We also measured FLI in hens that had become photorefractory, transferred to short photoperiods for 1 week--an insufficient time period to reverse photorefractoriness--and then exposed to long photoperiods for 48 h (photostimulated-photorefractory group). FLI was nearly absent in the tuberal hypothalamus of non-photostimulated-photosensitive hens but FLI was abundant in photostimulated-photosensitive hens. FLI was greatly reduced (P<0.01) in the rostral tuberal hypothalamus of photostimulated-photorefractory hens. All hens showed variable extra-tuberal FLI in locations associated with stress, e.g., paraventricular nucleus, lateral septal area, and nucleus taenia. Double-label fluorescence immunohistochemistry with c-fos antiserum and anti-Neu-N, a neuron-specific protein, showed that a substantial fraction of tuberal FLI-positive cells in photostimulated-photosensitive hens were neuronal. These results implicate neurons in the rostral tuberal hypothalamus as a potential neural locus of photorefractoriness, as FLI in this region appears coupled with cGnRH I activation in photostimulated-photosensitive but not photostimulated-photorefractory turkey hens.

Photoresponsiveness of turkey breeder hens changes during the egg-laying season: relative and absolute photorefractoriness.

Photosensitive species undergo neuroendocrine changes during a reproductive season that cause them to gradually become unresponsive to a photoperiod that initially stimulated reproduction. They may first become relatively photorefractory (rPR), when they will cease egg laying only if photoperiod is reduced, and then absolutely photorefractory (aPR), when they will cease laying despite long day length. Our objective was to test the photoresponsiveness of breeder turkey hens during egg production at various times following photostimulation and to relate photoresponsiveness to rPR and aPR as well as plasma levels of prolactin (PRL) and luteinizing hormone (LH). Hens were maintained in cages in light-controlled facilities and photostimulated at 31 wk of age (September) with a photoperiod of 16L:8D. At 8, 14, and 20 wk after photostimulation, treated hens received a 2-wk exposure to an 11.5L:12.5D photoperiod and were then returned to 16L:8D. Exposure to the shortened photoperiod at 8 wk of photostimulation resulted in three distinct responses of declining egg production: nonresponders (NR, 32.7% of hens), partial responders (PAR, 43.9%), or full responders (FR, 23.4%). Egg production returned to control levels following return to a 16L:8D photoperiod. This response repeated at the 14- and 20-wk treatment periods but with greater declines in egg production in the NR and PAR groups. The incidence of subsequent aPR in the NR, PAR, and FR groups was 5.7, 8.5 and 24%, respectively, as compared to 23.3% for the controls. Plasma LH and PRL concentrations also declined in response to 11.5L:12.5D and also rebounded following return to 16L:8D. The hormonal responses of NR, PAR, and FR were similar. We conclude that turkey hens exhibit varying degrees of rPR early during the egg laying season and that the incidence and severity of the rPR response increases as the laying season progresses. Further, PRL and LH levels did not reflect the differences in egg production among the responder and nonresponder groups to changes in photoperiod.

Melatonin enhances cellular and humoral immune responses in the Japanese quail (Coturnix coturnix japonica) via an opiatergic mechanism.

It is known that melatonin has important immunomodulatory properties in the Japanese quail. However, the mechanism of melatonin action on the immune system is not clearly understood in avian species. In mammals, the immunostimulatory properties of melatonin are mediated by the release of opioid peptides from activated T-lymphocytes. The present study was performed to determine if these same melatonin-induced opioids (MIO) are involved with the immunoenhancing effects of melatonin in quail. Three treatment groups were given melatonin (50 microg/ml) in the drinking water ad libitum along with naltrexone, a known opioid receptor-blocking agent. Melatonin was administered throughout the 3 week study and each bird received a daily intramuscular injection of naltrexone at a dose of 0.1, 1.0, or 10.0 mg/kg. In addition, three control groups were established that received only melatonin, naltrexone, or diluent. Evaluation of the cellular and humoral immune responses was initiated after 2 weeks of treatments. A cutaneous basophil hypersensitivity reaction to phytohemagglutinin (PHA-P) was measured to evaluate the cellular immune response. To evaluate the humoral immune response, primary antibody titers were determined 7 days post-intravenous injection with a Chukar red blood cell (CRBC) suspension. Both the cellular and humoral immune responses were significantly increased by 22 and 34%, respectively, upon melatonin exposure as compared to quail receiving diluent only. Concomitant administration of naltrexone and melatonin significantly reduced the immunoenhancing effect of melatonin across all naltrexone doses. We conclude that melatonin enhances a cellular and humoral immune response in Japanese quail via an opiatergic mechanism.

Immune function in turkey breeder hens during the short day prelighting period and renewal of photosensitivity for egg production.

Photorefractoriness (PR) in the turkey breeder hen is characterized by a lack of responsiveness to photoperiods that previously induced or maintained egg production. The consequence of PR is spontaneous regression of ovarian function and cessation of lay. Photosensitivity (PS) may be regained by giving at least 8 wk of short photoperiod (8L:16D) (light restriction). Following the transition from PR to PS, the birds may be photostimulated with long photoperiods, which allows for the recrudescence of ovarian function and normal egg production. Although the return of reproductive viability is the parameter for determining the successful recycle of ovarian function, there are no known reports of the physiological costs of this transition on immune function in the turkey breeder hen. We conducted an experiment to determine the immune responsiveness at various stages of recycle in the turkey breeder hen. Fifty photorefractory birds were selected and distributed equally among five treatment groups (time points). All birds were given an 8-wk period of light restriction (8L:16D) followed by a 12-wk period of photostimulation (16L:8D). The cellular (cutaneous basophil hypersensitivity CBH) and humoral (antibody titer) immune responses were determined in each treatment group (sequential time points): prelight restriction, 2-wk light restriction, 7-wk light restriction, 2-wk photostimulation, and 12-wk photostimulation. After 2-wk light restriction, there was a reduction in the cellular (64.1%) and humoral (59.5%) immune responses from that of the PR hens at the start. After 7-wk light restriction, the humoral responses increased (33.5%) as compared to the 2-wk light restriction time point Upon photostimulation, both the cellular (23.3%) and humoral (52.4%) immune responses were reduced at 2 wk of photostimulation as compared to the prior 7-wk light restriction time point. Finally, there was a rise in cellular (45.7%) and humoral (72.3%) immune responses after 12 wk of photostimulation as compared to the prior 2-wk photostimulation time point. We concluded that recycling of PR turkey hens was associated with altered cellular and humoral immune responses characterized by initial decline then recovery in both the light restriction and the postphotostimulation periods.

Melatonin can produce immunoenhancement in Japanese quail (Coturnix coturnix japonica) without prior immunosuppression.

In recent years, it has been determined that melatonin has important immunostimulatory properties in mammalian and avian species. Typically, this immunoenhancement has only been examined in immunosuppressed animals. The effect of melatonin on normal (unsuppressed) immune systems is yet to be evaluated in avian species. An experiment was performed to determine if transient and/or continuous melatonin treatments could enhance immune functions in Japanese quail without prior immunosuppression. All quail were kept on a short photoperiod (8:16LD) throughout the study. In this experiment, 50.0 microg/ml melatonin was provided ad libitum to adult Japanese quail in the drinking water either continuously or for 3h per day. Control birds received diluent continuously throughout the experiment. Both the cellular and humoral immune responses were determined immediately after 3 weeks treatment. A cutaneous basophil hypersensitivity reaction to phytohemagglutinin (PHA-P) was measured to evaluate the cellular immune response. To evaluate the humoral immune response, primary antibody titers were calculated 7 days post-intravenous injection with a Chukar red blood cell (CRBC) suspension. The cellular and humoral immune responses were significantly elevated in the transient (3h) and continuous (24h) melatonin treatment groups as compared to the control group (0 h). As compared to the control group, the cellular immune response was increased 25% and 38% for the 3 and 24h melatonin treatments, respectively. The humoral immune response was increased 26% and 32% for the 3 and 24h melatonin treatments, respectively. Furthermore, continuous (24h) melatonin availability significantly increased the cellular, but not humoral immune responses as compared to the transient (3h) group, given melatonin for 3h prior to the scotophase (13:00-16:00 h). From these data, it was clear that transient and continuous administration of melatonin increased the cellular and humoral immune responses of Japanese quail without prior immunosuppression. These data suggest that the immunoenhancing effect of melatonin is not limited to reconstitution of weakened immune systems, but can be observed in normal, immunologically unsuppressed birds.

Apposition of enkephalinergic axons with cGnRH I-containing perikarya in turkey hen brain.

Several lines of evidence support a role of endogenous opioids in the brain's regulation of gonadotropin secretion in birds and mammals, although the neuroanatomic basis of such regulation is not clear. We used double-label fluorescence immunohistochemistry employing polyclonal antisera raised in sheep against chicken gonadotropin-release hormone I (cGnRH I) and in rabbits against met-enkephalin to determine whether the potential exists for synaptic contact between neurons containing these neuropeptides in the preoptic/septal region of domestic turkey breeder hens. The cGnRH I antiserum was highly specific for cGnRH I, while the met-enkephalin antiserum showed some cross-reactivity with leu-enkephalin. We found numerous instances in which enkephalinergic neuronal elements appeared to contact cGnRH I perikarya and axons in and around the diagonal band of Broca, the bed nucleus of the pallial commissure and in the lateral septal nucleus. These appositions, confirmed by confocal scanning microscopy, appear to provide a neuroanatomic basis for how enkephalinergic innervation might influence gonadotropin secretion in turkey hens by directly regulating activity of cGnRH I neurons.

Relative and absolute photorefractoriness in turkey hens: profiles of prolactin, thyroxine, and triiodothyronine early in the reproductive cycle.

An experiment was conducted to determine whether a commercial strain of turkey hens exhibits relative photorefractoriness (rPR) during a reproductive cycle and to ascertain whether plasma levels of certain hormones early in the reproductive cycle might be associated with subsequent expression of rPR or absolute photorefractoriness (aPR). Twenty-seven percent of hens maintained on a stimulatory photoperiod of 18L:6D for 19 wk and then given a shorter, but still stimulatory, photoperiod (13L:11D) ceased to lay and their ovaries regressed within 4 wk. These hens were considered rPR. Subsequent exposure to the 18L:6D photoperiod resulted in ovarian recrudescence in 41.7% of these PR individuals, confirming the presence of rPR at 19 wk after photostimulation. Absolute PR was observed in 15.1% of hens during a 27-wk reproductive season. Hens that became rPR or aPR exhibited significantly lower plasma prolactin levels at 8 and 14 wk after photostimulation than did hens that remained photosensitive (PS). Plasma levels of thyroxine were lower at 1 and 2 wk following photostimulation in hens that subsequently became PR than in hens that remained PS. We conclude that turkey hens may exhibit rPR and aPR during a reproductive cycle, whereas flockmates may remain PS for at least 27 wk. The presence of long daylengths, thyroid hormones, and PRL did not assure expression of PR. The expression of PR appears to be associated with reduced plasma throxine levels during a period when programming of PR is thought to occur and with reduced levels of prolactin following peak egg production.

Circulating thyroid hormone levels in recycled turkey breeder hens during a short day prelighting period and renewal of photosensitivity for egg production.

Two experiments were conducted with yearling turkey hens at the end of their first season of egg laying. The purpose was to examine changes in plasma thyroid hormone levels during recycling and renewal of photosensitivity for egg production. Plasma concentrations of thyroid hormones were determined weekly or biweekly for 8 wk following a change from existing photoperiods of long days (LD) to short days (SD) and during the associated complete renewal (recycling) of photosensitivity for egg production. In both experiments, neither thyroxine (T4) nor triiodothyronine (T3) declined from starting values during the SD exposure but plasma T3 increased significantly from LD controls. There were no significant treatment effects (SD vs. LD) for T4 in either experiment. The increase in T3 was 101 and 145% in Experiments 1 and 2, respectively, and extended over the 8-wk SD treatment period in a parabolic fashion. The T3/T4 ratio was also significantly increased in the SD treatments of both experiments as compared to LD controls. Plasma concentrations of T3, but not T4, clearly changed during recycling and renewal of photosensitivity for egg production in breeder hens. These results were consistent with a participation of plasma T3 in promoting photosensitivity and diminishing photorefractoriness in turkey hens during SD-induced recycling.

Pineal melatonin secretion, but not ocular melatonin secretion, is sufficient to maintain normal immune responses in Japanese quail (Coturnix coturnix japonica).

Reports that plasma melatonin is an important immune regulator in avian species have been rather sparse and contradictory. Also, the primary source of immune-modulating melatonin has yet to be determined in birds. In Japanese quail (Coturnix coturnix japonica), the pineal gland and eyes contribute roughly two thirds and one third of the melatonin found in the blood, respectively. Two experiments were conducted to evaluate melatonin as an immune modulator in Japanese quail and to determine the primary source of immune-modulating melatonin in this species. Experiment 1 was designed to evaluate the involvement of the pineal gland and the eyes in immunocompetence. Each of three groups of quail was assigned a surgical treatment and the cellular and humoral immune responses were determined 8 weeks following surgery. The surgical treatments were pinealectomy (Px), sham pinealectomy (SH-Px), and ocular enucleation (eye removal (Ex)). Experiment 2 utilized exogenous melatonin as a replacement to reconstitute immune responses in surgically immunocompromised birds. In this experiment, 50.0 microg/ml of melatonin, or diluent only, was provided to Px and SH-Px birds in the drinking water ad libitum. The cellular and humoral immune responses were determined after 8 weeks of melatonin treatment. In both experiments, a cutaneous basophil hypersensitivity reaction to phytohemagglutinin was measured to evaluate the cellular immune response. To evaluate the humoral immune response, primary antibody titers were determined 7 days postintravenous injection with a Chukar red blood cell suspension. Flow cytometric analysis of peripheral blood lymphocytes was performed to determine the relative percentage of CD4(+) and CD8(+) T- and B-lymphocytes in all treatments of Experiment 2. In Experiment 1, both the SH-Px and Ex surgical treatments produced similar cellular and humoral immune responses, and these responses were significantly greater than those in Px-treated birds. Pinealectomy significantly reduced the cellular and humoral immune responses from SH-Px by 25.8% and 41.3%, respectively. In Experiment 2, Px again resulted in depressed cellular and humoral immune responses. In addition, Px significantly reduced CD8(+) T-lymphocyte numbers compared to SH-Px, while B-lymphocytes remained unchanged. Melatonin administration to Px birds increased the cellular (32.9%) and humoral (30.6%) immune responses to the level of control (SH-Px) birds, although this reconstitution was not due to increased CD8(+) T- or B-lymphocytes. From these data, it was clear that removal of the pineal gland, but not the eyes, reduced cellular and humoral immune responses, which were reconstituted to normal levels by exogenous melatonin. These data suggest that immunodepression is only observed in birds with two thirds of the plasma melatonin removed by pinealectomy. Removal of one third of the plasma melatonin (by ocular enucleation) is not sufficient to reduce cellular and humoral responses in the Japanese quail.