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Photostimulation of retinal photoreceptors appears to inhibit reproductive activity in birds. In the present study, the involvement of serotonin and vasoactive intestinal peptide was investigated in relation to reproductive failure associated with retinal photostimulation. Hens at 23 wk of age were divided into six rooms equipped with individual cages. At 24 wk of age, three rooms were photostimulated (14L:10D) with white light (control). Three rooms had two parallel lighting systems, red (660 nm) and green (560 nm), which were both on during 6 h of the 14-h light period. Upon photostimulation, the red light was turned off after 6 h, and the green light was left on for a total of 14 h (Green). Five hens from each room served as controls, five hens were immunized against vasoactive intestinal peptide, and five hens received parachlorophenylalanine, an inhibitor of serotonin biosynthesis. Parachlorophenylalanine treatment increased reproductive performance and mRNA expression of GnRH-I, LH-beta and FSH-beta (P < 0.05) in the Green group to levels which did not differ from those of the White (control) group. Immunization against vasoactive intestinal peptide reduced plasma concentration and pituitary mRNA expression of prolactin but did not affect expression of gonadal axis genes. Collectively, the results suggest that retinal photostimulation inhibits the reproductive axis through serotonin and not through vasoactive intestinal peptide.

The purpose of this study was to examine the role of vasoactive intestinal peptide (VIP) in prolactin (PRL) release in young turkey poults. Poults obtained from hens immunized with keyhole limpet hemocyanin (KLH)-chicken VIP (cVIP-KLH) conjugate or with KLH alone were used in this study. Plasma VIP antibody was tested by means of monoiodinated cVIP. Plasma samples were prediluted (1:100) in 0.05 EDTA PBS and used as a source of primary antibody in a cVIP-binding assay. Antibody levels averaged 50.8 +/- 10.3% at hatch and then declined with age to a level of 5.0 +/- 2.1% after 3 wk. Plasma PRL concentration was lower in cVIP-KLH-immunized poults (p < 0.05) than in KLH-immunized birds. Exogenous VIP administration at 7 days of age (7.8 micrograms/kg) increased plasma PRL level (p < 0.05) to a peak value of 359 +/- 32 ng/ml in the KLH-immunized birds. A smaller increase (p < 0.05) was obtained when the KLH-immunized poults received injections at 2 and 3 wk of age. The PRL response to cVIP administration was not observed in 1- and 2-wk-old poults maternally immunized with cVIP-KLH. Similarly, electrical stimulation of the ventromedial nucleus of the hypothalamus, at 1 and 8 days of age, induced a significant increase in the plasma PRL level of maternally KLH-immunized birds but not in maternally cVIP-KLH-immunized birds. These findings suggest that cVIP is a PRL-releasing factor in young turkey poults, similar to the finding in adult turkey hens.

Photostimulation of retinal photoreceptors appears to inhibit reproductive activity in birds. In the present study, the involvement of serotonin and vasoactive intestinal peptide was investigated in relation to reproductive failure associated with retinal photostimulation. Hens at 23 wk of age were divided into six rooms equipped with individual cages. At 24 wk of age, three rooms were photostimulated (14L:10D) with white light (control). Three rooms had two parallel lighting systems, red (660 nm) and green (560 nm), which were both on during 6 h of the 14-h light period. Upon photostimulation, the red light was turned off after 6 h, and the green light was left on for a total of 14 h (Green). Five hens from each room served as controls, five hens were immunized against vasoactive intestinal peptide, and five hens received parachlorophenylalanine, an inhibitor of serotonin biosynthesis. Parachlorophenylalanine treatment increased reproductive performance and mRNA expression of GnRH-I, LH-beta and FSH-beta (P0.05) in the Green group to levels which did not differ from those of the White (control) group. Immunization against vasoactive intestinal peptide reduced plasma concentration and pituitary mRNA expression of prolactin but did not affect expression of gonadal axis genes. Collectively, the results suggest that retinal photostimulation inhibits the reproductive axis through serotonin and not through vasoactive intestinal peptide.

The effect of exogenous ovine prolactin (oPRL) on preovulatory follicle P450 17 alpha-hydroxylase (C17) and aromatase (ARO) mRNA abundance was investigated in turkeys. Ovine PRL (124 IU/hen per day) was injected i.m. into four sets (n = 8) of laying turkeys for 2, 4, 8, or 14 days. Vehicle was injected into control hens for 8 days (n = 8). Blood samples were collected and serum was assayed for LH, progesterone (P), testosterone (T), and estradiol (E). Theca layers from the largest (F1) and the third (F3), fifth (F5), and seventh (F7) largest preovulatory follicles and from small white follicles (SWF) were examined for C17 and ARO mRNA contents. The number of atretic follicles increased from 0 (vehicle-injected controls) to 9 (14-day-oPRL-injected hens). Serum E, T, and LH levels decreased, while P levels remained unchanged. There was a transient increase in theca C17 mRNA abundance of 2- and 4-day-oPRL-treated hen follicles. Cytochrome P450 ARO mRNA levels were reduced in SWF and F7 in response to oPRL. Thecal C17 and ARO mRNA content was reduced during follicular maturation in laying hens. ARO mRNA was not detectable in granulosa cells. The progressive decline in C17 and ARO mRNA content associated with follicular maturation as well as the absence of ARO mRNA in granulosa cells is consistent with the secretory activity of P, T, and E in preovulatory follicles. These findings suggest that reduced circulating E may be a consequence of suppressed ARO gene expression whereas the oPRL suppression of T secretion may not be coupled to C17 gene expression.

Vasoactive intestinal peptide (VIP) is a hypothalamic prolactin (PRL)-releasing factor in the turkey. The hypothesis in the present study was that active immunization of turkeys with VIP would neutralize endogenous VIP, decrease circulating PRL, and consequently prevent the expression of incubation behavior. Large white female turkeys were divided into three experimental groups comprising untreated controls, control turkeys immunized with keyhole limpet hemocyanin (KLH), and turkeys immunized with synthetic chicken VIP conjugate (KLH-cVIP). Each turkey received four injections at 4-wk intervals, starting on the day of photostimulation. The immune response, measured by the percentage binding of monoiodinated chicken VIP (cVIP) to plasma at a dilution of 1:1000, averaged 11.8 ± 2.5% during the reproductive life cycle. Immunization against KLH-cVIP prevented the normal increases of PRL that are associated with the photo-induced reproductive cycle. Over a 21-wk period beginning at photostimulation, KLH-cVIP-immunized birds exhibited a maximal plasma PRL level of 82.2 + 29.5 ng/ml, compared to 367.7 + 66.6 ng/ml and 227.5 + 51.7 ng/ml for non- and KLH-immunized turkeys, respectively. The total number of nest visits per hen during the 147-day experimental period decreased from 320.0 ± 48.2 in the nonimmunized controls to 180.7 53.7 and 149.4 ± 13.1 visits in KLH- and KLH-cVIP conjugate-immunized turkeys. Turkeys that showed an immune response to KLH-cVIP immunization did not exhibit incubation behavior, whereas 54% and 33% of non- and KLH-immunized hens incubated their eggs. The latter two groups laid 58.4 ± 7.2 eggs and 65.6 ± 9.9 eggs per hen, respectively, compared to 87.6 ± 3.1 eggs per hen for the KLH-cVIP-immunized turkeys. It is concluded that the increased egg production observed in KLH-cVIP-immunized turkeys is the result of failure to express incubation behavior due to lower PRL levels.

The Saharan sand viper, Cerastes vipera (Linnaeus, 1758), is distributed in all Saharan countries, being confined to sand and dune systems. This relatively small snake, up to 35 cm, is nocturnal, is active from spring to autumn (April to October) and hibernates during the winter (November to March). We predicted that C. vipera would have peak plasma testosterone concentration at mating and that the vas deferens would contain abundant spermatozoa at that time. To test our predictions, we collected information on the time of mating and measured monthly testosterone concentration, testes size and testicular activity in free-living male C. vipera during its active period from April to October. Mating occurred only during spring. The pattern of plasma testosterone concentration, testes volume, seminiferous tubule diameter and spermatogenesis all followed the general pattern of high values in autumn and spring and low values in early summer. Our predictions were partially supported. There was a high plasma testosterone concentration at mating in spring and the vas deferens contained abundant spermatozoa, as predicted, but there was also a high plasma testosterone concentration in autumn without mating. We concluded that: (1) males are both aestival in that they produce spermatozoa in autumn, which they store over the winter hibernation period, and vernal in that they produce spermatozoa in spring prior to mating; (2) matings are associated with spermatogenesis; and (3) the high plasma testosterone concentration is concomitant with both matings and spermatogenesis in spring and with spermatogenesis in autumn. We propose that C. vipera has a single peak of testicular activity and plasma testosterone concentration which start in autumn and end in spring. We also propose that spermatogenesis is prior to spring mating and, consequently, is prenuptial.

Vasoactive intestinal peptide (VIP) is the avian prolactin releasing factor and changes in the concentrations of plasma prolactin (PRL) are found during the avian reproductive cycle. This study investigated the changes in the VIP/PRL system of native Thai hens rearing their young as compared to hens deprived of rearing their chicks. The number of VIP-immunoreactive (VIP-ir) neurons in the Nucleus inferioris hypothalami (IH) and Nucleus infundibuli hypothalami (IN) of hens rearing chicks (R) were compared with those of non-rearing chicks (NR). Plasma PRL levels were determined by enzyme-linked immunosorbent assay. The localization and number of VIP-ir neurons were determined by immunohistochemistry. The numbers of VIP-ir neurons in the IH–IN areas were high in the R hens, whereas the number of VIP-ir neurons decreased in the NR hens as compared to their respective R hens. During the rearing period, changes in the VIP-ir neurons within the IH–IN were correlated with plasma PRL levels. The results of the present study indicate for the first time that the VIP/PRL system plays a role in neuroendocrine reorganization to establish maternal behavior in native Thai chickens. The VIP/PRL system functions not only as a well established key regulator of incubation behavior, but is also involved in the regulation of rearing behavior. It is possible that VIP and the decline in the number of VIP-ir neurons and in turn VIPergic activity and the decrease in PRL levels are related to their contribution to rearing behavior of this non-seasonal breeding, equatorial precocial species.

The Saharan sand viper (Cerastes vipera) and the crowned leafnose (Lytorhynchus diadema) are two snake species well adapted to desert sand dunes and, in Israel, coexist in the western Negev Desert. C. vipera is a sit-and-wait ambusher while L. diadema is an active hunter. We studied the seasonal and diel activity patterns and dietary selection of these two species while free-living in the field. Both species were active from early spring until late fall but displayed (i) different seasonal activity patterns -C. vipera was bimodal with peaks in spring and autumn whereas L. diadema was basically unimodal with a peak in summer; (ii) different nocturnal above-ground activity patterns -C. vipera was active mainly during the first three hours of darkness while L. diadema was constantly active during the first seven hours of darkness; and (iii) different patterns of nocturnal behavior -C. vipera moved up to 50 m while L. diadema moved several hundred meters each night. Dietary selection differed between these snake species although lizards, mainly Nidua fringe-fingered lizards (Acanthodactylus scutellatus), were the main dietary item for both. We concluded that temporal partitioning in above-ground activity, different foraging strategies and differences in dietary selection may contribute towards the coexistence of the two snake species.

This study was designed to examine changes in cytochrome P450 17a-hydroxylase (C17) and aromatase (ARO) mRNA contents in the theca layer of preovulatory follicles (POF) as turkey hens transit from egg laying to incubation. Hens were grouped into the following categories: 1) laying hens-laid one egg per day and nested 1-2 times per day; 2) transitional hens-laid one egg per day and nested > 4 times per day; and 3) Day 1, Day 3, and Day 5 incubating hens-laid no eggs for 2, 4, or 6 days, respectively, and nested > 4 times per day. Small white follicles (SWF) and the theca layer from the largest (F.) and the third (F3), fifth (F 5), and seventh (F 7 ) largest POF were dispersed and challenged with testosterone (T) for 5 h. Relative levels of C17 and ARO mRNA were examined from the theca layers of F 1, F3, F, F 7, and SWF. The number of atretic follicles increased from O (layers) to 8 (Day 5 incubating hens). Serum LH, progesterone (P), and estradiol (E), but not T, declined on Day 1 of incubation. Basal levels of P, T, and E from theca and SWF cells declined in incubating hens. Both basal and T-stimulated theca and SWF production of E decreased in incubating hens. C17 and ARO mRNA declined in SWF, F 7, and F5 during follicular atresia. It is suggested that reduced gene expression of ovarian steroidogenic enzymes may be a partial determinant of reduced circulating sex steroid levels in incubating hens. Follicular maturation is associated with a progressive decrease in C17 and ARO mRNA steady state levels as the follicle matures; this may partially explain the decreases in T and E secretion that are associated with follicular maturation.

Hyperprolactinemia is associated with incubation behavior in avian species. Increased nesting activity is a major indication of incubation behavior. Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion from the anterior pituitary. The goal of this study was to induce incubation behavior by stimulating PRL through chronically infusing VIP into the third ventricle of turkey brains. In experiment 1, porcine VIP (pVIP) was infused into the median eminence at a rate of 60 ng/min for 7 days by means of osmotic pumps implanted s.c.. Plasma PRL increased significantly in the pVIP-treated turkeys (p < 0.001). Although egg laying was not affected by the pVIP infusion, the mean oviduct weight decreased (p < 0.057). In experiment 2, saline or pVIP (30 or 60 ng/min) was infused into the third ventricle of laying turkeys for 12 days. Both pVIP treatments increased plasma PRL for 9 days (p < 0.05). The 30-ng pVIP/min infusion decreased nesting activity, plasma LH, ovary and oviduct weight, hypothalamic GnRH I, and anterior pituitary VIP receptors (p < 0.1). However, ovine PRL infusion (20.8 ng/min) into the same turkey flock increased nesting activity (p < 0.01). In conclusion, pVIP does not induce incubation behavior in laying turkeys.

An inverse relationship often exists between prolactin (Prl) and LH in avian species. Our study was designed to investigate the relationship between hypothalamic and posterior pituitary vasoactive intestinal peptide (VIP)--an endogenous Prl-releasing peptide--and chicken GnRH-I and GnRH-II. Hypothalamic VIP content was increased after photostimulation, reaching its highest levels in incubating and photorefractory birds. The highest hypothalamic GnRH-I content was in laying hens followed by that in photostimulated and incubating birds. The lowest levels were in the nonphotostimulated birds. Hypothalamic GnRH-II increased after photostimulation, then fell to nonphotostimulated levels during incubation and photorefractoriness. Posterior pituitary VIP content was elevated in response to photostimulation, reaching a peak value in the laying and incubating birds, then declining in the photorefractory hens. Posterior pituitary GnRH-I and GnRH-II content peaked in the incubating birds. Ovariectomy caused a significant reduction in hypothalamic GnRH-I and GnRH-II with no effect on VIP; no changes were found in the posterior pituitary due to ovariectomy. Reducing day length caused a significant decrease in the hypothalamic and the posterior pituitary content of VIP and GnRH-I, and GnRH-II. Ovine Prl (oPrl) administration to laying hens reduced the hypothalamic VIP and GnRH-I and GnRh-II content. Posterior pituitary GnRH-I content was also reduced. Although GnRH-II levels were reduced by Day 4 of injections, they rose to peak levels by Day 14 of oPrl administration. Posterior pituitary VIP content was not altered by oPrl.

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin-releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels. 2. The increase in hypothalamic GnRH-I content which occurs during sexual development was advanced in TAM-treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth. 3. Plasma LH concentrations behaved similarly and were higher in the TAM-treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM-treated than in control birds; plasma GH values were not consistently affected by TAM treatment. 4. Both the growth and the involution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks. 5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.

The effect of ovine prolactin (oPRL) administration to laying and incubating turkey hens was studied. In experiment one, five treatment groups (n = 6) of laying hens received injections of vehicle or oPRL (4 mg/bird/day) for 2, 4, 8, or 14 days. Hypothalamic vasoactive intestinal peptide (VIP) content decreased to its lowest level (p < 0.05) by Day 2 of oPRL injection. Serum turkey PRL decreased by Day 8 of injection, reaching nadir by Day 14. Similar to the decline in hypothalamic VIP content, the maximal decline in the number of anterior pituitary VIP binding sites was achieved by Day 2 of oPRL administration. Hypothalamic GnRH-I content decreased after 2 days of oPRL injection and remained low through Day 14 of the experiment. GnRH-II levels declined with time, reaching significantly lower levels after 8 days of injections, and remained low through Day 14. Plasma LH levels also declined (p < 0.05) after Day 14 of oPRL administration. In experiment 2, two groups (n = 6) of incubating birds were used: controls receiving injections of vehicle only and birds receiving injections of oPRL (4 mg/bird/day) for 10 days. Exogenous oPRL had no effect on hypothalamic VIP, GnRH-I or II, anterior pituitary VIP binding sites, or plasma turkey PRL or LH. The findings suggest that in laying hens, PRL inhibits its own secretion by acting on both the hypothalamus and the anterior pituitary; this phenomenon does not occur in incubating birds. Furthermore, we provide evidence that pRL acts centrally to reduce LH levels by reducing GnRH levels in the hypothalamus.

Vasoactive intestinal peptide (VIP) is a prolactin-releasing factor in turkey hens. Membranes from anterior pituitaries of turkey hens were used to characterize VIP receptors. Using HPLC-purified monoiodinated VIP, we found specific VIP receptors in the anterior pituitary glands. Binding was saturable and was time- and temperature-dependent. Scatchard analysis of competitive binding studies indicated two binding sites, a high-affinity binding site (Kd1) of 6.6 +/- 1.8 pM and maximum binding (Bmax1) of 1.52 +/- 0.2 pM, and a low-affinity binding site (Kd2) of 542 +/- 200 pM and Bmax2 of 15.8 +/- 8.0 pM. Binding of VIp to pituitary membranes was specific, as compared to other peptides of the glucagon family. The rank order of potency of the peptides tested was chicken VIP > porcine VIP > peptide histidine isoleucine > secretin > glucagon > growth hormone-releasing factor. Two binding sites were found in all the examined reproductive stages. The lowest binding site levels were found in nonphotostimulated and photorefractory birds, followed by photostimulated birds and layers; highest levels were found in incubating birds. Nest deprivation significantly reduced Bmax1 levels without changing hypothalamic VIP content. These results suggest the involvement of the anterior pituitary VIP receptors in the regulation of prolactin secretion from the pituitary gland.

As a consequence of its fundamental role in avian reproduction, incubation behavior has been of great interest to scientists and to turkey breeders and producers of hatching eggs. Incubation behavior in turkey hens continues to be a major hindrance to enhanced reproductive performance in the domestic turkey, resulting in substantial loss of potential egg production. The onset and maintenance of incubation behavior is dependent upon a series of obligatory factors. Nest entry induced by progesterone surges in laying hens, which is dependent on prior estrogen priming, is a prerequisite for prolactin (Prl)-induction of incubation behavior. Thereafter, persistent nesting stimulates Prl secretion and elevated Prl levels maintain incubation activity. The increased Prl secretion in incubating hens is related to a diminished dopaminergic and an increased vasoactive intestinal peptidergic activities in the hypothalamus. An increase in Prl gene expression and Prl releasing capacity of the pituitary may also contribute to the hyperprolactenimic state in the incubating bird.

A series of experiments were conducted to elucidate the role of the ovary in incubation behavior-associated luteinizing hormone (LH) suppression. Ovariectomy (Ovx) increased (p 0.05). Ovx had no effect on intramuscularly injected mammalian luteinizing hormone-releasing hormone (4 µg/kg i.m. > induced LH in incubating hens, but enhanced the LH response in laying hens. Serum LH and prolactin (Prl) were unaffected by Ovx, and nest deprivation (ND) decreased Prl levels (p

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 (660nm) and green (560nm), which were both on during 6 out of 14h of the light period. Then, in 3 of these rooms, the green light was turned off and hens were exposed to a total of 14h 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 14h (Green, n=45). The Green group had reduced egg production; reduced plasma concentrations of ovarian steroids; reduced luteinizing hormone (LH)-β, vasoactive intestinal peptide (VIP), and prolactin mRNA expression; and greater retinal green opsin mRNA expression ( P ≤ 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 ≤ 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.

To achieve the ultimate goal of both cryosurgery and cryopreservation, a thorough understanding of the processes responsible for cell and tissue damage is desired. The general belief is that cells are damaged primarily due to osmotic effects at slow cooling rates and intracellular ice formation at high cooling rates, together termed the "two factor theory." The present study deals with a third, largely ignored component--mechanical damage. Using pooled bull sperm cells as a model and directional freezing in large volumes, samples were frozen in the presence or absence of glass balls of three different diameters: 70-110, 250-500, and 1,000-1,250 microm, as a means of altering the surface area with which the cells come in contact. Post-thaw evaluation included motility at 0 h and after 3 h at 37 degrees C, viability, acrosome integrity, and hypoosmotic swelling test. Interactions among glass balls, sperm cells, and ice crystals were observed by directional freezing cryomicroscopy. Intra-container pressure in relation to volume was also evaluated. The series of studies presented here indicate that the higher the surface area with which the cells come in contact, the greater the damage, possibly because the cells are squeezed between the ice crystals and the surface. We further demonstrate that with a decrease in volume, and thus increase in surface area-to-volume ratio, the intra-container pressure during freezing increases. It is suggested that large volume freezing, given that heat dissipation is solved, will inflict less cryodamage to the cells than the current practice of small volume freezing.

Dopamine (DA) has a pivotal role in avian prolactin (PRL) secretion, acting centrally through D(1) DA receptors to stimulate PRL secretion by operating through vasoactive intestinal peptide (VIP). DA also inhibits PRL secretion by activating D(2) DA receptors at the pituitary level. This study was designed to investigate the distribution of DA neurons in the native Thai chicken, utilizing tyrosine hydroxylase (TH) as a marker for dopaminergic neurons. The differential expression of hypothalamic TH immunoreactive (TH-ir) neurons was also compared across the reproductive cycle. The results revealed that TH-ir neurons and fibers were found throughout the brain of the laying hen and were predominantly located within the diencephalon and mesencephalon. The observed distribution pattern of TH immunoreactivity was consistent with that reported previously in several avian species. However, changes in the number of TH-ir neurons in the nucleus intramedialis (nI) were observed across the reproductive cycle and correlated directly with variations in PRL levels. The population of TH-ir neurons in the nI increased significantly during the egg incubation period, where circulating PRL levels were the greatest. This study indicates, for the first time, that an association exists between DA neurons and the regulation of the reproductive system in the native Thai chicken. There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species and it is suggested that the differential expression of DA neurons in the nI might play a role in the control of VIP secretion and subsequent PRL release in such birds.

1. The effects of early exposure of heavy breed (HB) chicks to an anti‐oestrogen (tamoxifen—TAM) and to an androgen which cannot be aromatised (5α‐dihydrotestosterone—DHT) on subsequent adiposity and its response to testosterone were studied. 2. Embryonic TAM administration reduced adiposity in females but not in males at 8 weeks of age. Embryonic DHT produced similar responses but to a lesser extent. 3. Testosterone propionate (TP) administration during growth had no effect on adiposity in any of the treated groups but TP reduced adiposity in males which had been exposed to DHT at the embryonic stage.

Reproductive failure associated with heat stress is a well known phenomenon in avian species. Increased prolactin (PRL) levels in response to heat stress have been suggested as a mechanism involved in this reproductive malfunction. To test this hypothesis, laying female turkeys were subjected to 40°C for 12 h during the photo-phase daily or maintained at 24–26°C. Birds in each group received oral treatment with parachlorophenyalanine (PCPA; 50 mg/kg BW/day for 3 days), an inhibitor of serotonin (5-HT) biosynthesis; or immunized against vasoactive intestinal peptide (VIP). Both treatments are known to reduce circulating PRL levels. Non treated birds were included as controls. In the control group, high ambient temperature terminated egg laying, induced ovarian regression, reduced plasma luteinizing hormone (LH) and ovarian steroids (progesterone, testosterone, estradiol) levels, and increased plasma PRL levels and the incidence of incubation behavior. Pretreatment with PCPA reduced (P< 0.05) heat stress-induced decline in egg production, increase in PRL levels, and expression of incubation behavior. Plasma LH and ovarian steroid levels of heat stressed birds were restored to that of controls by PCPA treatment. As in PCPA-treated birds, VIP immunoneutralization of heat-stressed turkeys reduced (P< 0.05) circulating PRL levels and prevented the expression of incubation behavior. But it did not restore the decline in LH, ovarian steroids, and egg production (P> 0.05). The present findings indicate that the detrimental effect of high temperature on reproductive performance may not be related to the elevated PRL levels in heat-stressed birds but to mechanism(s) that involve 5-HT neurotransmission and the induction of hyperthermia.

Our previous studies demonstrated that illumination of chicken embryos with monochromatic green light results in enhanced body and muscle weight at later posthatch stages. In the present study, we investigated the cellular and molecular basis of this phenomenon. First, we showed that on day 6 posthatch, myofibers were more uniform in the in ovo illuminated group than in the control group incubated in the dark, with respect to the number of myofibers displaying diameter values within the range of the mean value. Second, we tested the hypothesis that in ovo illumination causes an increase in the number of myoblasts; this in turn can promote posthatch muscle growth. Indeed, a significant increase in the number of skeletal muscle cells isolated from pectoralis muscle was observed in the in ovo illuminated group on days 1 and 3 posthatch relative to the control group. This increased cell number was accompanied by higher expression levels of Pax7 and myogenin proteins on posthatch days 1 and 3, respectively. A parallel analysis of proliferating cells in the intact muscle further demonstrated a significant increase in the number of cells positive for proliferating cell nuclear antigen in muscle from the in ovo illuminated group. Third, we demonstrated that the transition from fetal- to adult-type myoblasts, normally occurring in late stages of chicken embryogenesis, is initiated earlier in embryos subjected to in ovo green-light illumination. We suggest that the stimulatory effect of in ovo illumination on posthatch muscle growth is the result of enhanced proliferation and differentiation of adult myoblasts and myofiber synchronization.

The paired-box transcription factor Pax7 plays a critical role in the specification of satellite cells in mouse skeletal muscle. In the present study, the position and number of Pax7-expressing cells found in muscles of growing and adult chickens confirm the presence of this protein in avian satellite cells. The expression pattern of Pax7 protein, along with the muscle regulatory proteins MyoD and myogenin, was additionally elucidated in myogenic cultures and in whole muscle from posthatch chickens. In cultures progressing from proliferation to differentiation, the expression of Pax7 in MyoD+ cells declined as the cells began expressing myogenin, suggesting Pax7 as an early marker for proliferating myoblasts. At all time points, some Pax7+ cells were negative for MyoD, resembling the reserve cell phenotype. Clonal analysis of muscle cell preparations demonstrated that single progenitors can give rise to both differentiating and reserve cells. In muscle tissues, Pax7 protein expression was the strongest by 1 day posthatch, declining on days 3 and 6 to a similar level. In contrast, myogenin expression peaked on day 3 and then dramatically declined. This finding was accompanied by a robust growth in fiber diameter between day 3 and 6. The distinctions in Pax7 and myogenin expression patterns, both in culture and in vivo, indicate that while some of the myoblasts differentiate and fuse into myofibers during early stages of posthatch growth, others retain their reserve cell capacity.

The original objectives were: A. To determine the critical embryonic age for monochromatic green light stimulation. B. To follow the ontogeny of embryos exposed to monochromatic green light vs. darkness. C. To investigate the effects of monochromatic green light illumination on myoblast and fiber development in the embryo. D. To investigate the stimulatory effect of light combinations during embryo and post-hatch periods on growth and meat production. E. To evaluate the direct effect of monochromatic green light on cultured embryonic and adult myoblasts. The overall purpose of this study was to investigate the effect of monochromatic light stimuli during incubation period of broilers on muscle development and satellite cell myogenesis. Based on previous studies (Halevy et al., 1998; Rozenboim et al., 1999) that demonstrated the positive effects of green-light illumination on body and muscle growth, we hypothesized that monochromatic light illumination accelerates embryo and muscle development and subsequently enhances muscle growth and meat production. Thus, further decreases management costs. Under the cooperation of the laboratories at the Hebrew University of Jerusalem and University of Washington we have conducted the following: 1. We have established the critical stage for exposure to green monochromatic light which has the maximal effect on body and muscle growth (Objective A). We report that embryonic day 5 is optimal for starting illumination. The optimal regime of lighting that will eliminate possible heat effects was evaluated by monitoring egg core temperature at various illumination periods. We found that intermitted lighting (15 min. on; 15 min. off) is optimal to avoid heat effects. 2. We have evaluated in detail gross changes in embryo development profile associated to green light stimuli vs. darkness. In addition, we have investigated the stimulatory effect of light combinations during embryo and post-hatch periods on body and muscle growth (Objective B,D). 3. We have studied the expression profile of muscle regulatory proteins during chicken muscle cell differentiation in cultures using newly developed antibodies. This study paved the way for analyzing the expression of these proteins in our photo stimulation experiments (Objective C). 4. We have studied the pattern ofPax7 expression during myogenesis in the posthatch chicken. Experimental chick pectoralis muscles as well adult myoblast cultures were used in this study and the results led us to propose a novel model for satellite cell differentiation and renewal. 5. The effects of monochromatic green light illumination during embryogenesis have been studied. These studies focused on fetal myoblast and satellite cell proliferation and differentiation at pre- and posthatch periods and on the effects on the expression of muscle regulatory proteins which are involved in these processes. In addition, we have analyzed the effect of photo stimulation in the embryo on myofiber development at early posthatch (Objective C). 6. In follow the reviewers' comments we have not conducted Objective E. The information gathered from these studies is of utmost importance both, for understanding the molecular basis of muscle development in the posthatch chicks and for applied approach for future broiler management. Therefore, the information could be beneficial to agriculture in the short term on the one hand and to future studies on chick muscle development in the embryo and posthatch on the other hand.

1. Four methods of semen collecting that involved interruption of mating in two breeding ostrich pairs were tested: an artificial vagina was tested without promising results; the funnel method, in which a funnel was placed under the phallus of the tested male immediately after mating allowing semen drips to be collected; the vacuum method, using a turkey semen collector, inserted into the seminal canal; and the tube method, conducted by placing a test tube inside the seminal canal, allowing semen to enter by gravity. 2. For the funnel, vacuum and tube methods, respectively, average semen volume was 0.1 +/- 0.02, 1.12 +/- 0.22, and 0.58 +/- 0.13 ml, sperm concentration was 0.66 +/- 0.14, 2.35 +/- 0.26, and 2.13 +/- 0.27 x 10(9) cells/ml, and percentage of abnormal cells was 5.82 +/- 1.79%, 4.68 +/- 1.19%, and 7.09 +/- 1.72%. 3. Semen characteristics varied throughout the reproductive season reaching peak concentration in June-July. 4. The vacuum method proved to be the most efficient and was a low stress, restraint-free method for collecting ostrich semen.

Artificial illumination, including light quality, is important in modern meat-type poultry management. In the present study, the effect of in ovo monochromatic green light photostimulation on posthatch growth of turkey poults was investigated. In experiment 1, 182 turkey eggs were divided into two light treatment groups (n = 91). The first group was intermittently photostimulated (3 min on and 3 min off) with green light provided by five light-emitting diodes (LED) per egg at 0.1 W/m2 at the upper eggshell surface. The second group was incubated in the dark and served as the control. Posthatch BW were recorded at 0, 2, 6, 13, 20, 28, 35, and 59 d of age. A heavier BW, occurring at 28 d of age and persisting until the end of the experiment (59 d of age), was observed in the in ovo green light stimulated females as compared to their corresponding controls. In experiment 2, 273 turkey eggs were divided into three light treatment groups (n = 91). The first group was intermittently photostimulated (15 min on and 15 min off) with green light provided by seven LED per egg at 0.14 W/m2. The second group was photostimulated with white light provided by one mini-incandescent lamp per egg at light intensity and schedule similar to the first group. Eggs of the third group were incubated in the dark and served as controls. Posthatch BW were recorded at 0, 7, 14, 28, 42, 56, and 79 d of age. No differences were found among the BW of males incubated under different light conditions. As in experiment 1, female turkeys with stimulated green light in ovo had greater BW compared to their corresponding control and white light groups from 28 d of age until termination of the experiment at 79 d of age. Breast muscle weight was greater in female turkeys incubated under green light when compared to white and dark incubation treatment groups. We suggest that in ovo green light photostimulation enhances the posthatch BW of female turkey poults.

The effect of early posthatch feeding on skeletal muscle growth and satellite cell myogenesis was studied in turkey poults. Poults were either fed immediately posthatch or food-deprived for the first 48 h and then refed for the rest of the experiment. Body and breast muscle weights were lower in the starved poults than in fed controls throughout the experiment (P < 0.05). Cultures of breast muscle satellite cells revealed significantly higher DNA synthesis in the fed group than in the starved group as early as d 1 (P < 0.05). These levels continued to rise, reaching approximately 500-fold those of feed-deprived poults on d 4. In the latter group, thymidine incorporation peaked only on d 6, and then declined. Thereafter, it decreased to the same levels as those in the fed group. Satellite cell number per gram muscle increased until d 4, and was higher in the fed group than in the starved group (P < 0.05). Pax7 levels in cell cultures derived from the fed group were markedly higher than in the starved group on d 2 (P < 0.05). Myogenin levels in both culture and muscle were higher in the fed than in the starved groups until d 4 (P < 0.05). Phosphorylation of the survival factor Akt and cyclin-dependent kinase inhibitor p21 levels were higher in cells derived from the fed group relative to those from the starved group 48 h posthatch (P < 0.05). Similarly, Akt phosphorylation and insulin-like growth factor I (IGF-I) levels were significantly higher in the muscles of the fed group (P < 0.05). Together, these results suggest that immediate posthatch feeding of poults is critical for satellite cell survival and myogenesis probably via IGF-I.

High temperature stress is of major concern to turkey producers in Israel and the United States. The decline in the rate of egg production at high environmental temperature is well recognized, but the neuroendocrinological basis is not understood. Our objectives were: 1) to characterize the hypothalamo-hypophyseal axis involvement in the mechanism(s) underlying the detrimental effect of heat stress on reproduction, and 2) to establish procedures that alleviate the damaging effect of heat stress on reproduction. Heat stress (40oC, Israel; 32oC, U.S.) caused significant reduction in egg production, which was restored by VIP immunoneutralization. The decline in egg production did not appear to be entirely related to the expression of incubation behavior due to the rise in circulating PRL in stressed birds. Heat stress was found to increase circulating PRL in ovariectomized turkeys independent of the reproductive stage. Active immunization against VIP was shown for the first time to up-regulate LHb and FSHb subunit mRNA contents. These findings taken together with the results that the heat stress-induced decline in egg production may not be dependent upon the reproductive stage, lead to the suggestion that the detrimental effect of heat stress on reproductive performance may be in part mediated by VIP acting directly on the GnRH/gonadotropin system. Inhibin (INH) immunoneutralization has been shown to enhance FSH secretion and induces ovulation in mammals. It is hypothesized that immunization of heat-stressed turkeys against INH will increase levels of circulating FSH and the number of preovulating follicles which leads to improved reproductive performance. We have cloned and expressed turkey INH-a and INH-bA. Active immunization of turkey hens with rtINH-a increased pituitary FSH-b subunit mRNA and the number of non-graded preovulatory yellow follicles, but no significant increase in egg production was observed.

Ambient temperature modulates prolactin (PRL) secretion in birds. It is not known whether this modulation directly affects the PRL controlling mechanism(s) or whether it indirectly influences them through the onset of sexual maturity and/or the onset of incubation behavior. These experiments were designed to investigate the effect of elevated (32 degrees ) and reduced (10 degrees ) ambient temperatures on PRL secretion. Somatically mature, ovariectomized female turkeys were used to avoid the confounding effects of reproductive stage, nesting, and egg stimuli on PRL secretion. Hens were ovariectomized 5 weeks before, on the day of, or 10 days after the inception of photostimulation. Temperature treatments included chronic exposure (5 weeks) to 32 or 10 degrees and acute exposure (i.e., temperature was reversed from 32 to 10 degrees or from 10 to 32 degrees on or after the day of photostimulation). Chronic exposure to either 32 or 10 degrees had no effect on the rise in serum PRL that followed photostimulation in both sham-operated controls and ovariectomized hens. Acute exposure to 10 or 32 degrees altered the photoperiodically stimulated rise in plasma PRL. Birds switched from 10 to 32 degrees showed a significantly greater PRL increase than birds shifted from 32 to 10 degrees. Ovariectomy enhanced the PRL response to the gonadal stimulating photoperiod. The effect was most pronounced in hens photostimulated prior to ovariectomy. These findings suggest that ambient temperature and/or ovariectomy have a modulating effect on the PRL response to long days.

Laying hens held in battery cages in naturally ventilated poultry houses in hot countries usually develop hyperthermia, which adversely affects their performance. The present means of cooling alleviate to some degree, but cannot eliminate, the stress imposed by heat. A new approach to cooling of laying hens was developed, based on wetting the skin and promoting evaporation of water from the ventral regions of the bird. The type of plumage in the ventral regions and the exposed skin of the apteria enable more efficient wetting than is possible with dorsal cooling. A ventral cooling regime, comprising an initial period of frequent wettings followed by intermittent wetting for 10 s every 30 min was able to maintain normothermia of laying hens subjected to a 10-h period of heat exposure. Dorsal cooling was less efficient; body temperature and respiration rate were higher and skin temperatures were lower than in ventrally cooled hens. During 10 d of heat exposure, ventrally cooled hens maintained egg weight and shell index (mg/cm2), whereas their food intake decreased moderately. In contrast, egg weight, shell index, and food intake all decreased markedly in uncooled or dorsally cooled hens. Transient alterations in plasma concentrations of corticosterone, progesterone, and estradiol were noted in uncooled and dorsally cooled hens but not in ventrally cooled hens. Results indicate that ventral cooling is an efficient method to alleviate heat stress in laying hens during summer. Successful implementation of ventral cooling in poultry houses will depend on optimal installation of sprinklers and on minimal wetting of manure.

The importance of late winter pairing activity on the neuroendocrinology of wild waterfowl is unknown. In this study, we examined the sex-related differences in the roles of late winter pairing activity and seasonal influences on neuroendocrine and reproductive physiology in both male and female mallards. Our main goals were to determine (1) which physiological responses were influenced by pairing status or by seasonal changes and (2) whether responses differed between the sexes. Thus, physiological responses of mallards in different pairing status categories were assessed at two times: January 28 to February 5 and February 24 to March 3. Ducks were assigned to one of the following pairing status categories: strong pairs, temporary pairs, unpaired or lone birds within the flock, or birds isolated in same-sex groups. Seasonal changes correlated with increases in both gonadal mass and hypothalamic content of vasoactive intestinal peptide in both sexes, whereas only pairing status correlated with changes in body mass in both sexes. The main sex-related differences were the following: (1) Seasonal decreases in hypothalamic gonadotrophin releasing hormone II content occurred only in females. (2) Seasonal increases in serum prolactin occurred only in males, whereas levels in females were low throughout the study. (3) Both male and female gonadal masses increased seasonally, but male gonadal mass was initially twice that of females. (4) Body mass of both sexes was influenced by pairing status correlations (i.e., all paired or lone birds were heavier than isolated birds), but body mass in males decreased seasonally. No sex-related differences occurred in hypothalamic gonadotrophin releasing hormone I content or circulating serum luteinizing hormone. Taken together, these results indicate that seasonal reproduction in mallards is regulated not only by seasonal but also by social cues, and differences occur between the sexes, months in advance of actual breeding.

1. The effect of light intensities from 10 to 700 lux on the performance of 5 to 18 week-old turkey males was studied in 2 trials. 2. Body weight of 18 week-old turkeys, in both experiments, was highest under the lowest light intensity. This coincided with higher weight gain and lower food intake, which resulted in significantly better food conversion efficiency. 3. Light intensity affected heart muscle weight but not weight of breast muscle, abdominal fat or testis as proportions of body weight. 4. The decline in plasma T 3 concentration with age differed from other treatments at the low light intensity, which resulted in a significantly higher T 3 concentration in turkeys exposed to 10 lux at the age of 10 to 15 weeks. 5. It is concluded that light intensity significantly affects food conversion efficiency in turkey males. this is likely to be related to differential investment of energy expenditure for maintenance.

The aim of this study was to determine the effect of different light sources and light schedules on the growth and quality of commercial broilers. In each experiment 810 broiler chicks were divided into 3 groups, 3 replicates per group. All were reared at 20 lux. Body weight and food consumption were recorded weekly. Experiment 1. Birds were reared under 3 light sources: incandescent light bulb, warm-white fluorescent light tube or warm-white mini-fluorescent light bulb. Experiment 2. Birds were reared on 3 light schedules. 23 h light and 1 h dark (23L: 1D) throughout; an increasing light schedule with initial 23L:1D then 8L: 16D increasing daylight gradually to 16L:8D or an intermittently increasing daylight schedule (16:8P) where light and dark periods were shorter but portioned to achieve the same total hours per day up to 16L:8D. Broilers reared under mini-fluorescent light bulb were heavier than those under fluorescent tubes or incandescent bulbs by 49 d. Until 42 d of age, photoperiod had no effect on growth. However, at 49 d broilers reared under 16:8P and 16L:8D regimens were heavier than those or 23L:1D. At 42 d, female broilers on 23L:1D, were heavier than those on 16L:8D and 16:8P. Mortality was higher in groups on 23L:1D than on 16L:8D on 16:8P. At 49 d incidence of leg condemnation was higher in the 16:8P group. However, skin damage was lower in this group than in those on 23L: 1D and 16L:8D.

Tamoxifen (TAM) is an antiestrogen that advances sexual puberty in cockerels, turkey toms, and Muscovy drakes. The effect of TAM on semen-fertilization capacity in White Leghorn (WL) male chicks was assayed in the present study. Sixty, 2-wk-old, male chicks were divided into two equal groups. The chicks from one group were injected im with 1 mg of TAM per kg of BW every other day, those from the second group were vehicle-treated (with corn oil) and served as controls. Each chick was paired with a virgin, WL laying hen. When semen was produced, the paired female was inseminated twice a week. The results revealed that TAM administration caused the early production of fertile semen, which resulted in the first normal descendants as early as 8 wk of age arid brought about 100% of parenthood by the age of 88 days.

The effects of Tamoxifen (TAM) on reproductive traits in young turkey toms and Muscovy drakes were studied. At 6 wk of age, five toms were injected every other day with 1 mg TAM/kg BW, while six others were treated with corn oil (controls). In the toms, using TAM advanced semen production by 4 wk (13.5 versus 17.5 wk of age) and increased the size of the snood and testes. Similarly, in the Muscovy drake, using TAM enhanced penis growth and advanced semen production by 5 wk.

The time course of comb development and estrogen levels were compared in broiler (BX) and layer (LX) females that consumed feed ad libitum (A) or were subjected to quantitative feed restriction (R). The chicks were reared under short photoperiod [(6 h light (L):18 h dark (D)] until 22 wk of age. At this time, photoperiod was increased in one step to 8L:16 D, and then gradually increased until 14L:10D at 34 wk. There was a significant interaction between genetic type and feeding treatment, such that entry into lay of the LX-R and BX-R females was delayed by 1 and 4 wk, respectively, relative to the LX-A and BX-A birds. Mean comb size of LX-A birds began to increase while still under 6L:18D photoperiod; that of the other treatment groups did not begin to increase until photoperiod was shifted to 8L:16D. Comb size of individual LX-A, LX-R, and BX-A birds began to increase about 8 wk prior to individual onset of lay; that of BX-R birds about 11 wk prior to onset of lay. In all groups, estrogen levels remained low until 3 to 4 wk prior to onset of lay, when they showed a sharp increase. Following onset of lay, estrogen levels of all groups remained high. Critical day length of LX-A birds appears to be lower than that of BX-A birds. In addition, feed restriction per se appears to decrease photoperiod responsiveness of BX birds.

1. Mule ducks were produced by naturally mating Muscovy drakes and Khaki Campbell ducks. 2. Semen was collected from 6-month-old mule drakes via an artificial vagina. The fluid was clear without any spermatozoa or spermatids. 3. Testes from 27-week-old mule drakes were smaller in size than those of Khaki Campbell drakes but heavier than Muscovy males of the same age. Histological sections of these testes revealed that spermatogenesis was not complete. 4. Testosterone concentration in the mule drakes was higher than in Muscovy males but similar to Khaki Campbell drakes. 5. Mule drakes have strong sexual drives as a result of high concentrations of testosterone, but, because spermatogenesis is incomplete, their semen had no sperm.

In this study we addressed the effect of various monochromatic light treatments on muscle growth and satellite cell proliferation in broilers (Gallus domesticus). Broilers were reared under green (560 nm), blue (480 nm) and red (660 nm) monochromatic lights and white light as a control from day one until 35 days of age. At five days of age, satellite cells were prepared from the experimental chicks. The number of satellite cells per gram of breast muscle and total number of satellite cells derived from the experimental broilers was substantially higher in the groups reared under green and blue light, compared to the red and white light groups. Growth hormone receptor gene expression was also higher in the former groups. High correlation was found between the breast muscle weight observed on day 35 and the number of satellite cells per gram of breast muscle (r = 0.915) and total number of satellite cells (r = 0.833), derived from the experimental chicks as early as five days of age. In addition, the protein/DNA ratio found in breast muscle at 35 days of age was significantly lower in chicks that were reared under green and blue lights. The lowest ratio which was found in the green group and was twice as low as in the control group, indicates the highest number of nuclei in the former group. As satellite cells are the only source of additional nuclei in skeletal muscles of postnatal animals, our results suggest that the higher muscle weight found in the green and blue light groups was due to increased satellite cell proliferation during the first days of age.

The effect of yohimbine, an alpha 2-adrenergic blocker, on the reproductive activity of 12-year-old male, captive Nile crocodiles was tested on 18 animals equally divided into 3 ponds. In each pond, there were 6 males and 30 females. In the first group, six of six males received yohimbine capsules of 30 mg, twice a day, for 1 week. In the second group, two males of a group of six were administered a similar dose of yohimbine. Another group of six males in a separate pond were used as a control group. The yohimbine treatment had a significant (p less than 0.05) effect on the frequency of headslap display (the main behavioral pattern of reproductive activity) in all treated animals but did not result in a significant increase in copulation frequency. In the two treated groups, the reproductive period was prolonged by 3 weeks, 8-11 weeks. We found a significant increase in the fertility percentage of eggs laid by females in the male-treated groups (30.5% in control group females, 34.1% in the partly treated, and 39.0% in the pond where all six males were treated), even though no increase in mating frequencies was noted. This might be due to more successful copulations. During the treatment period, the daily activity peak, when the male's headslap performance was the most frequent, was shifted from 5:00-6:00 p.m. in the control to 4:00-5:00 p.m. in the treated group. This effect caused females to enter the water earlier than in the control group.

1. Tamoxifen (TAM) administration advances puberty in cockerels. In the present study the effect of TAM administration on the sexual development of White Leghorn hens was studied. 2. Two-week-old White Leghorn females were injected intramuscularly with TAM on alternate days at doses of 0.1 mg (0.1 TM), 1 mg (1TM), 5 mg (5TM) and 10 mg/kg body weight (10TM) respectively, while the controls were injected with maize oil (vehicle). The experiment was terminated at 23 weeks of age, when all the control hens laid eggs. Sample autopsies were made on chicks of 6, 14 and 23 weeks of age. 3. Body growth was not affected by any of the treatments. 4. Comb growth was accelerated by all doses of TAM, while hematocrit increased in the 1TM, 5TM and 10TM hens. 5. Egg laying advanced in the 0.1TM and 1TM birds, was delayed in 5TM hens and did not occur at all in the 10TM females. 6. TAM caused a precocious increase in plasma oestrogen and androgen, suppressed adiposity in a dose-related manner and, at low doses, advanced the development of the gonadal system. 7. At 23 weeks of age, when the gonadal system of the controls was fully active, TAM caused a dose-related depression in abdominal fat, liver, ovary, and oviduct weights, plasma total lipids and calcium concentrations and a dose-related increase in plasma oestrogen and androgen titres, and comb weight. 8. It seems that TAM increased gonadotropic activity and its androgen stimulating action, but suppressed peripheral signs of the elevated plasma oestrogen titres. Low doses of TAM enhanced gonadotropic activity and egg laying but the antioestrogenic effect depressed development of the gonadal system, suppressing egg production when high doses were administered. It therefore seems that oestrogens are necessary for normal ovarian development in hens.

The leaning role, previously suggested for testosterone in chickens, was tested in males and females of fatty and lean breeds. The breeds used were the White Leghorn (WL), of which the male is very lean, and the White Giant (WG) and the White Cornish X White Rock (WCWR), in which both sexes accumulate fat. Castration of WL males induced adiposity and replacement therapy with testosterone propionate (TP) reduced the fat to normal. However, in males of the fatty breeds, neither castration nor TP administration had any effect on adiposity. Similarly, long-term supplementation of a high dose of TP had no effect on the level of adiposity in females of both the heavy and the light breeds. Thus, the leaning effect found for testosterone in the WL male is not a general phenomenon in chickens but rather a specific response of the WL male.

1. The effect of early exposure of heavy breed (HB) chicks to an anti-oestrogen (tamoxifen--TAM) on later adiposity was studied. 2. TAM administration at the embryonic stage, but not at the day of hatching, reduced adiposity in females but not in males, at 8 to 9 weeks of age. This reduction in adiposity in females minimised or even alleviated the excess of fat in females compared to males.

Fifty White Leghorn male chicks were divided into five equal groups of ten chicks each. Beginning at two weeks of age they were injected on each alternate day as follows: corn oil as a vehicle control or 0.5, 1.0, 5.0, or 10.0 mg tamoxifen/kg/b.wt. The whole experimental period lasted until twelve weeks of age. The two lowest doses of tamoxifen (TAM) enhanced comb growth, while the highest dose suppressed it. The two lowest doses of TAM also caused an earlier increase in sexual activity of the chicks, and precocious production of semen. At nine weeks of age the 0.5 and 1.0 mg doses of TAM increased plasma testosterone to a level three times higher than in the controls. This effect was not observed with the highest dose of TAM. At 12 weeks of age the chicks treated with 1 mg TAM had larger testes than the controls and produced three times more sperm per ejaculation. At this stage chicks treated with the highest dose of tamoxifen produced less sperm than the control and had smaller testes and adenohypophyses.

To examine the effects of tamoxifen, a known estrogen antagonist in the chicken, two groups of cockerels were injected every other day from hatching until 7 weeks of age with 1 and 10 mg tamoxifen/kg body weight (BW), respectively. A third group was injected with 1 mg tamoxifen/kg BW every 3 days from 5 to 10 weeks of age. All groups treated with tamoxifen had increased testes weight, but BW and pituitary weights did not differ from controls. In contrast to controls, seminiferous epithelium of testes from treated cockerels showed spermatogenesis up to the spermatid elongation stage. We suggest that the antiestrogen effect of tamoxifen increased circulating LH, which stimulated testes growth and precocious spermatogenesis.

White Leghorn male chicks were injected with 1 mg/kg BW of tamoxifen (an anti-estrogen) on alternating days between 2 and 9 wk of age. This treatment increased testes weight and induced semen production in response to the abdominal massage procedure. Insemination of laying hens with this semen resulted in hatching of live chicks from their eggs.