A homologous radioimmunoassay for turkey prolactin: changes during the reproductive and ovulatory cycle

Photostimulated prolactin release in the Turkey hen: effect of ovariectomy and environmental temperature

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.

LH responses to chicken luteinizing hormone-releasing hormone I and II in laying, incubating, and out of lay turkey hens

An experiment was conducted to assess the relative in vivo and in vitro activities of chicken LH-RH-I and -II in laying, incubating and out-of-lay turkey hens. The highest plasma concentrations of LH were measured in laying turkey hens, whereas hypophyseal concentrations were highest in incubating hens (I) and lowest in the laying hens at the end of the laying period (EL). Hypophyseal and plasma concentrations of LH decreased with aging in laying hens (L) and the greater decrease occurred in the hypophyses. An in vitro hypophyseal acute challenge with 2-min pulses of cLHRH I or II (10(-7) M) using a perifusion technique resulted in an increase in the release of LH in out-of-lay (OL) and incubating (I) hens, but not in laying (L) hens. Although both peptides elicited comparable responses in I hens, cLHRH II was more effective in OL hens. This difference was attributable to a greater amplitude of the response, whose duration was unchanged. Hypophyseal desensitization to a subsequent stimulation was observed in OL hens when the interval between stimulations was 30 min, but this did not occur at 60- or 120-min intervals. In vivo, the injection of cLHRH I or II, at doses of 10(-8) and 10(-10) M/kg B.W. stimulated increases in the plasma concentrations of LH, which were initiated within 1 min of injection in OL and I hens but from 5 to 20 min postinjection in L hens. The responses were dose-related and greater immediate responses were measured with cLHRH I than with cLHRH II. Also, after the injection of cLHRH II at the 10(-8) M/kg B.W. dose, the shape of the LH response consisted of an initial increase, followed by a more sustained phase during which LH concentrations were either stable (I hens) or continued to increase (L and OL hens) from 20 to 60 min after injection. In contrast, the injection of cLHRH I at doses of 10(-8) or 10(-10) M/kg or cLHRH II at a dose of 10(-10) M/kg in I and OL hens, produced a peak of LH concentrations in plasma within 5 min and thereafter declined gradually. The difference in the in vivo responses to LHRH I and II could not be attributed to a greater potency of cLHRH II, but to a more prolonged action. In summary, the responses to both forms of chicken LH-RH varies markedly with the stage of the reproductive cycle (L, I, and OL) and differs between the in vivo and in vitro situations. Although cLHRH II may be more active than cLHRH I, controversy still surrounds its precise physiological role.

Changes in levels of immunoreactive prolactin isoforms during a reproductive cycle in turkey hens

Changes in the ratio between immunoreactive isoforms of prolactin using Western blotting and in the total prolactin content using radioimmunoassay were measured in pituitary glands from turkey hens at different physiological stages. The type of glycosylation (N- or O-linked carbohydrates) was determined using endoglycosidase digestion (N-glycosidase F, O-glycosidase, and neuraminidase). Low levels of prolactin were observed in pituitary glands from sexually immature, out-of-lay, and molting hens. Higher levels were present during the egg-laying period and the highest levels were detected in hens which expressed incubation behavior. Two immunoreactive bands of apparent molecular weights of 24 and 27 kDa were visualized on Western blots, corresponding to the nonglycosylated and glycosylated forms of prolactin, respectively. In pituitary glands from incubating turkey hens, about 70% of the prolactin was glycosylated (27-kDa isoforms), whereas about 60% was glycosylated in immature and in hens during the first egg-laying period. In pituitaries from out-of-lay and molting hens the percentage of glycosylated prolactin was 38 and 33%, respectively. Thus, higher percentages of glycosylated isoforms (27 kDa) were associated with high levels of total prolactin and lower percentages were associated with low levels of prolactin content in the pituitary gland. Digestion of the isoforms with N-glycosidase F resulted in a single band with an apparent molecular weight of 24 kDa. Partial deglycosylation was achieved using neuraminidase, whereas digestion with O-glycosidase had no apparent effect on the isoforms. Thus it appears that the glycosylated isoforms of prolactin have N-linked carbohydrates containing sialic acid.

Effects of environmental and social factors on incubation behavior, endocrinological parameters, and production traits in turkey hens (Meleagris gallopavo)

Hens raised in three different environments were assessed for changes in egg production performance, the rate of incubation behavior expression, and plasma levels of luteinizing hormone (LH) and prolactin for 20 wk following the laying of the first egg. The environments were individual (IFP) or collective floor pens (CFP) and individual battery cages (Cp and Cnp). The hens from three experimental groups (IFP, CFP, and Cp) were transferred from a short (6 h) to a long (14 h) photoperiod, whereas the ones from the remnant (Cnp) were left under a short one. Increase of the photoperiod induced significant increases (P < 0.05) in levels of prolactin and LH after 1 d, and resulted in the onset of egg laying in a delay of 14 d in all groups. However, the overall egg laying performance was highest for the IFP hens. The CFP and IFP hens laid 98 and 24% of their eggs inside the nest boxes, respectively. The hens raised in battery cages did not express incubation behavior, whereas 50 and 33%, respectively, of the CFP and IFP hens did. During the 1st wk of egg laying, levels of prolactin increased for all photostimulated hens but to a greater extent for CFP hens. Higher increases in levels of prolactin were associated with the expression of incubation behavior; however, prolactin levels of nonincubating laying hens were also higher under the CFP treatment. It appears that the rate of expression of incubation behavior, as well as changes in the plasma levels of prolactin and LH throughout an egg production period, are dependent upon rearing conditions in turkey hens.

Development and validation of a homologous radioimmunoassay using a biologically active recombinant turkey prolactin

1. A new homologous radioimmunoassay has been developed for the measurement of turkey prolactin. 2. A 25000 kDa purified recombinant derived turkey prolactin (rtPRL), the biological activity of which was tested using a crop sac assay, was used as immunogen for the production of rabbit antiserum. In this biological test, the rtPRL was as active as the ovinePRL. 3. The radioligand (rtPRL) was labelled with 125I and the assay allowed the detection of standard doses of rtPRL ranging from 400 pg/tube to 50 ng/tube. 4. No cross reaction with chicken luteinising hormone and recombinant chicken growth hormone was detected. 5. The within and between assay coefficients of variability were 5.0 +/- 2.7% and 16.3%, respectively. The overall mean recovery ratio was 1.01. 6. The dose-response curves obtained with serial dilution of plasma and pituitary from turkey hens at different physiological stages and from male turkeys were parallel to those obtained with standard rtPRL. 7. The measured concentration of prolactin was 5 times higher in plasma from incubating than laying turkey hens, and the pituitaries from incubating hens contained 2 and 4 times more prolactin than those of laying and out of lay hens or males, respectively. 8. To further assess the validity of the assay, we measured changes in plasma concentration of prolactin in turkeys following stimulation with chicken vasointestinal peptide (cVIP). A single injection of 1 or 10 micrograms/kg body weight of cVIP to laying hens produced a large and rapid increase in plasma prolactin. 9. This new radioimmunoassay appears to be high for the measurement of turkey prolactin.

High-level expression of biologically active chicken prolactin in E. coli

1. A large quantity of chicken prolactin (cPRL) was produced by manipulating the cPRL cDNA clone and an expression vector pKK223-3. To augment the production of the hormonal protein in E. coli, in addition to the potent tac promoter, a unique DNA linker containing a pair of Shine-Dalgarno sequences and a short preceding cistron sequence was inserted into adjacent 5'-region of the coding region. 2. In sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, recombinant cPRL protein exhibited a molecular mass of 23 kDa. 3. The recombinant cPRL showed equivalent binding kinetics to an antiserum raised against turkey PRL. Also, this product increased the weight of pigeon crop sac mucosa to a degree comparable to that induced by turkey PRL. 4. These results indicate that this recombinant cPRL has immunological and biological activities identical to those of authentic avian PRL.

Changes in endocrinological parameters and production performances in Turkey hens (Meleagris gallopavo) submitted to different broody management programs

Occurrence of broodiness, egg production, feed consumption index and changes in the LH and prolactin levels were compared for turkey hens raised under 3 broody management programs. All hens (n=60 per group) were regularly ejected from the nest (basic treatment). Moreover, one group of hens was also rotated weekly (partial treatment), while in the third group (full treatment) hens showing broody symptoms were also identified daily and isolated for 24 hours. The percentage of hens which were identified as broody at least once was similar under the 3 programs (30%), although the use of the full and partial programs were more effective in inducing the disruption and/or preventing further expression of broody behavior. Plasma LH concentrations decreased progressively throughout the reproductive cycle under the 3 treatments. Maximum plasma concentrations of prolactin were measured between the 5th and the 10th weeks of production; higher concentrations of prolactin were maintained for a longer period under the full treatment, while a lower amplitude rise in plasma prolactin concentrations was observed in the hens submitted to the partial treatment. The egg production and feed consumption indices were lower and higher, respectively, under the full treatment than the basic treatment and partial treatments. We conclude that management programs need to be carefully evaluated under commercial conditions not only with respect to broodiness expression but also to egg production.

Protein and energy self-selection of turkey hens. Serum prolactin and luteinizing hormone concentrations

1. The incidence of broodiness was four times as high among turkey hens fed a complete control diet than among hens allowed to self-select their diet from two different feed sources, one being relatively high in protein and the other relatively high in energy (i.e. split-diet). 2. Among non-broody birds, hens fed the split-diet had a significantly lower serum prolactin concentration in the third month of production as compared to control hens. 3. Hens in their second season of egg production had significantly lower serum luteinizing hormone concentrations during the latter stages of egg production than did first season hens.

Changes in the plasma concentrations of prolactin, luteinising hormone, progesterone and D-(beta)-hydroxybutyrate in turkey hens (Meleagris gallopavo), during treatment of broodiness under commercial conditions

1. An experiment was done under commercial conditions to investigate the physiological effects of isolating broody turkey hens, for 72 h, in sand and wire floored pens on the third, 10th and 16th weeks of production. 2. Hens identified as broody and removed from the flock had higher plasma prolactin concentrations than the laying hens at each of the three experimental stages. 3. Confinement in sand and wire floored pens, induced a decline in plasma prolactin concentrations. This decline probably impeded immediate development of broody behaviour. Alternately, levels of prolactin higher than those of laying hens were again measured 7 and 14 days after treatment during third week but not after the 10th and 16th week of production. 4. Confinement did not induce consistent changes in luteinising hormone (LH) and progesterone concentrations from one period to an other. 5. An increase in the plasma concentration of D-(beta)-hydroxybutyrate was observed in the hens which had an egg present in the oviduct on day 2, 3 and/or 4 of the treatment. Subsequently, a decrease in ovulation rate was observed in the hens with higher concentrations of D-(beta)-hydroxybutyrate while under treatment, during the 10th week of production. 6. These data confirm that the effectiveness of the traditional methods for broodiness prevention under commercial conditions is related to the induction of a decrease of prolactin.

Responses of luteinizing hormone and prolactin plasma concentrations to oral administrations of clomiphene citrate in broody turkey hens

Plasma levels in luteinizing hormone (LH) and prolactin were measured after oral administration of clomiphene-citrate (CC) at doses of 6 and 12 mg/kg BW/day for 5 consecutive days to broody turkey hens. No significant changes in prolactin levels were measured following treatment. The LH concentrations were significantly decreased (P less than .05) following administration of the 12-mg/kg dose. These results were interpreted as an indication of oestrogenic-like, rather than antioestrogenic-like, activity of CC when administrated to turkey hens at this particular physiological stage.

Turkey plasma thyroid hormone and prolactin concentrations throughout an egg laying cycle and in relation to photorefractoriness

Plasma concentrations of thyroxine (T4), triiodothyronine (T3), and prolactin were determined weekly through an egg laying cycle induced with 30 wk of 14 h light:10 h dark. Egg production, primary remige molting, and occurrence of photorefractoriness were monitored. Hens were assigned to one of two groups; those that exhibited photorefractoriness (PR) and those that remained photosensitive (PS). Weekly plasma T4 concentrations relative to the time of initiation of photostimulation did not differ between PR and PS groups; concentrations peaked prior to the onset of egg production, were lowest during peak egg production, and increased between Weeks 6 and 30 of photostimulation. Plasma T4 levels of PR hens peaked 3 wk prior to the onset of photorefractoriness. Plasma T3 concentrations of PS and PR hens were similar until increases occurred in PR hens at the onset of photorefractoriness. Plasma prolactin levels in PS and PR hens increased after photostimulation, declined sooner in PR hens, and were generally greater in PS than PR hens during the last 20 wk of the study. Mean time of onset of photorefractoriness in PR hens was 23.0 wk (range = 18 to 28 wk) after initiation of photostimulation. Egg production of PS hens was greater than that of PR hens after 20 wk of photostimulation, and PR hens molted a greater number of primary remiges than PS hens. Results indicated that 1) elevated plasma T4 may be involved in development of photorefractoriness in turkey hens, 2) increases in plasma T3 may be involved in gonadal regression and molting, and 3) elevated plasma prolactin was associated with persistence of photosensitivity.

Pineal and ocular influences on male and female turkeys: plasma luteinizing hormone and prolactin levels during gonadal development

Plasma levels of prolactin (PRL) and luteinizing hormone (LH) were determined in pinealectomized (PX) and/or bilateral ocular enucleated (EX) turkey hens and toms during gonadal development. Measurements were obtained weekly for 6 weeks following photo-induced ovarian recrudescence in adult hens and biweekly from 12 to 34 weeks of age in sexually developing toms. Both hens and toms were maintained on a photoperiod of 16L:8D. Plasma PRL levels were significantly correlated with time (P less than 0.01) and were linear with significant slopes (P less than 0.01) in all treatment groups of hens and toms. However, the regression coefficients were positive for the hens and negative for the toms. Both PX and EX reduced PRL levels in the hens. PX did not significantly affect PRL levels of toms but EX depressed PRL levels. In hens LH was not correlated with weeks of photostimulation but in toms LH was positively correlated to age and linear with significant slopes in all treatment groups. There were no significant treatment effects on plasma LH levels of hens or toms. It was concluded that neither the pineal gland nor the eyes affect plasma LH levels of male turkeys during testicular development or female turkeys during photostimulated ovarian recrudescence. Although the eyes affected plasma PRL of both males and females during gonadal development, the pineal only influenced female PRL levels.

Basal and hypothalamic extract-induced luteinizing hormone and prolactin secretion by cultured anterior pituitary cells from female turkeys in various stages of the reproductive cycle

The wet weight of the anterior pituitary gland of the domestic turkey increases as the hen progresses through the reproductive cycle. The greatest wet weight was observed with anterior pituitary glands from incubating hens, whose weight was twice that of anterior pituitary glands from nonphotostimulated hens. Anterior pituitary glands from hens in each of the various stages of the reproductive cycle were dissociated and cultured, and subsequently basal and hypothalamic extract (HE)-induced releases of prolactin (PRL) and luteinizing hormone (LH) were compared between cultures containing a defined number of anterior pituitary cells. Basal and HE-induced releases of PRL were greatest (P less than 0.05) in the cultures of anterior pituitary cells derived from incubating hens, with those of laying, photorefractory, and nonphotostimulated hens being successively less (P less than 0.05), respectively. HE-induced release of LH was greatest (P less than 0.05) in cell cultures derived from nonphotostimulated hens, with cultures of cells derived from laying, photorefractory, and incubating hens exhibiting successively smaller releases of LH (P less than 0.05), respectively. The concentration of HE that induced the first significant increase in the release of PRL or LH above that of basal levels also varied with the reproductive stage of the donor hens. The changes in circulating PRL levels during the various stages of the reproductive cycle reflect changes in anterior pituitary sensitivity to hypothalamic releasing activity and/or changes in the PRL releasing capacity of the anterior pituitary. In contrast, there does not appear to be a strong correlation between anterior pituitary LH releasing capacity in vitro and circulating LH levels in the domestic turkey hen.

Effect of pregnant mare serum gonadotropin on plasma prolactin, luteinizing hormone, estradiol, and ovarian growth in incubating and out-of-lay turkeys

The effect of pregnant mare serum gonadotropin (PMSG) on ovarian growth and estradiol production was assessed in out-of-lay (OL) turkey hens that have low plasma concentrations of prolactin (PRL) and in incubating hens that have high plasma levels of PRL. In OL hens after injection with 400 or 2,000 IU PMSG, plasma concentration of PRL did not change, whereas ovarian weight and plasma concentration of estradiol increased by greater than 20-fold to levels comparable to those of laying hens. Follicles were not arranged in a hierarchy following the injection of either 400 or 2,000 IU PMSG into OL hens. There was a linear relationship between the dose of PMSG injected into incubating hens and the subsequent increase in plasma concentration of estradiol. Plasma levels of PRL were not different among hens injected with 0, 16, 80, or 400 IU PMSG, whereas plasma levels of PRL decreased in incubating hens injected with 2,000 IU PMSG. A significant increase in ovarian weight occurred only in hens injected with 2,000 IU PMSG. None of the hens deserted the nest following the injection of PMSG, indicating that the maintenance of incubation does not require a steroidogenically quiescent ovary. Although the regressed ovaries of both OL and incubating hens are responsive to gonadotropin stimulation, it would seem that the higher levels of PRL in incubating hens may act, in part, to suppress PMSG-induced ovarian growth and steroidogenesis.

Characteristics of prolactin binding sites in the brain of the ring dove (Streptopelia risoria)

Radiolabeled ovine prolactin ([125I]oPRL) was found to bind specifically to crude membrane fractions prepared from ring dove brain homogenates. Specific binding changed with incubation time and temperature but did not fluctuate systematically with pH. Specific binding levels were highest in hypothalamus and forebrain and were lowest in cerebellum and brain stem. A linear increase in specific binding was observed in pooled midbrain and forebrain membrane fractions as membrane protein concentrations increased from 0.2 to 6.0 mg/ml. Scatchard analysis of binding saturation and competitive binding data revealed that dove midbrain/forebrain membranes bound oPRL with high affinity (Kd = 2.1-2.6 X 10(-10) M) but had low binding capacity (Bmax = 2.9-4.8 fmol/mg protein). Unlabeled oPRL and human growth hormone competed most effectively with radiolabeled oPRL for occupation of midbrain/forebrain binding sites. Turkey PRL and human placental lactogen were less effective as competitors but were 8-15 times more effective than ovine or turkey growth hormone, porcine insulin, or ovine luteinizing hormone. Subcutaneous injection of unlabeled oPRL lowered specific binding in liver and midbrain/forebrain by 76 and 39%, respectively, over that observed after saline injection. Prior MgCl2-induced desaturation of membrane binding sites greatly reduced or eliminated these treatment differences. These results suggest the existence of specific, saturable binding sites for PRL in dove brain which conceivably could mediate the reported effects of PRL on behavior and gonadal function in this species.

Plasma immunoreactive-growth hormone in domestic fowl: measurement by homologous and heterologous radioimmunoassays

Concentrations of immunoreactive (IR) growth hormone (GH) in the plasma of domestic fowl have been measured by homologous and heterologous radioimmunoassays and the estimates compared. Both assays detected an age-related decline in the circulating IR-GH concentration, an increase in IR-GH secretion following TRH-stimulation or fasting, and a fall in the IR-GH concentration following adrenocorticotropin administration. However, while the overall estimates of IR-GH concentration were significantly correlated, the magnitude of the changes in IR-GH concentration determined by the homologous assay were far greater than those detected by the heterologous system, which failed to show any inhibitory effect of anesthesia or exogenous thyroid hormones on basal or stimulated IR-GH release. These results suggest that the heterologous GH radioimmunoassay lacks the sensitivity of the homologous chicken GH assay and that circulating GH in birds is probably composed of heterogeneous moieties with differing immunoreactivities with rat GH antibodies.

Effect of environment on the intake of food and water, body weight, egg production and plasma concentrations of corticosterone and prolactin in turkey hens

During the first 4 weeks of egg production, there were no differences in the plasma concentrations of prolactin and corticosterone, egg production, body weight and the consumption of food and water between turkey hens which were maintained in cages or in floor pens. The plasma concentration of prolactin increased to the same extent in both environments during the period of peak egg production. A further rise in concentration of prolactin occurred in association with the termination of oviposition in 15 of the 19 hens which stopped laying eggs. Prolactin appeared to be progonadal and then antigonadal, once a threshold concentration was exceeded. This threshold value was higher in caged turkey hens. After laying ended, high concentrations of prolactin in hens maintained in cages were not maintained in the absence of a stimulus or stimuli associated with the nests.

The influence of prolactin on food intake of turkey hens

The effect of intracerebroventricular (ICV) injections of turkey prolactin on food intake of turkey hens was studied. Adult, nonlaying medium-weight turkey hens, exposed to 6 hr of light per day, were used in Experiment 1. In Experiments 2 and 3, medium-weight and large-weight turkey hens, respectively, exposed to a long photoperiod and in production, were used. Prolactin was injected into free-feeding hens at doses ranging from 800 to 3200 ng. The ICV injection of prolactin had no significant effect on food intake of hens maintained under 6 hr light per day and not in egg production. In hens exposed to long photoperiods and in egg production, the ICV injection of prolactin caused a significant decrease in food intake. These results suggest that prolactin, acting at the level of the central nervous system, decreases food intake in photostimulated turkey hens.

Seasonal changes in prolactin and luteinizing hormone in the polyandrous spotted sandpiper, Actitis macularia

The polyandrous spotted sandpiper (Actitis macularia) is a species characterized by female dominance over males and predominant male parental care. Prolactin (Prl) and luteinizing hormone (LH) were analyzed in plasma samples obtained serially from individuals across different stages of the breeding season. The reproductive status of each sampled individual was known in detail. Similar Prl values were obtained independently by two different assays. Males tended to have higher plasma Prl levels than females throughout the breeding season. Prl was significantly elevated in both sexes by the first few days of incubation. This rapid rise in Prl may indicate its role in brood patch development and the onset of incubation behavior. In males Prl continued to rise during incubation, whereas it remained constant in females. Higher levels of Prl in males than females, especially late in incubation, reflects the greater contribution of males to incubation. LH declined markedly in males and females from prelaying to early incubation. There was a significant negative correlation between Prl and LH among males, especially from the prelaying to early incubation phases of the season. There was no such correlation among females.

Influence of cerebroventricular injection of dopamine on plasma prolactin and LH levels of postlaying and broody turkey hens

Dopamine (DA), a well-known inhibitor of prolactin secretion in mammals, was injected into the third cerebroventricle of turkey hens in two distinct physiological states. Nonbroody postlaying turkeys had preinjection plasma prolactin (Prl) levels of about 68 ng/ml. Prolactin levels were significantly elevated 20 and 40 min after intraventricular injection of 10 micrograms of dopamine and then returned to basal levels. Incubating turkey hens, in contrast, showed the typical hyperprolactinemia characteristic of this physiological state. Mean preinjection Prl levels ranged from about 1290 to 1860 ng/ml. Injection of 10 or 30 micrograms of dopamine neither increased nor decreased plasma Prl levels over the 120-min time course of this experiment. Plasma luteinizing hormone (LH) levels were increased in nonbroody postlaying hens within 40 min after intraventricular injection of 10 micrograms of DA and then declined. Levels in vehicle-injected hens did not change significantly up to 120 min after injection. Dopamine injection had no effect on LH levels of broody turkey hens. These data clearly show that DA is not an inhibitor of Prl secretion in nonlaying turkeys with moderate Prl levels and in fact it appears to stimulate its release.

The relationship between plasma concentrations of prolactin and consumption of feed and water during the reproductive cycle of the domestic turkey

The plasma concentrations of prolactin (PRL) were measured throughout the reproductive cycle of turkey hens. Plasma PRL levels increased during egg laying from 20.1 +/- 3.9 ng/ml (means +/- SEM) at the first oviposition to 55.6 +/- 5.1 ng/ml at the last oviposition. Levels of PRL increased during incubation and were maintained between 70 and 90 ng/ml. After the poults were hatched, the concentration of PRL decreased rapidly and by 7 days after hatch, PRL levels were not significantly different from those observed before egg laying. The consumption of feed and water decreased significantly (P less than .05) during incubation to less than 10% of that observed during egg laying. The intake of feed and water increased rapidly after the poults were hatched. Hens lost 17% of their body weight during the incubation period. The concentration of D-(-)-3-hydroxybutyrate (DBHB) increased 16-fold during the incubation period and decreased rapidly after the poults were hatched. Body temperature and the concentration of glucose were significantly (P less than .05) depressed during incubation. Hematocrit increased significantly (P less than .05) during the transition from egg laying to incubation. These data suggest that the changes in the concentration of PRL may be related to the large changes in intermediary and water metabolism that occur during broodiness.

Regulation of prolactin and its role in gallinaceous bird reproduction

There are major changes in circulating luteinizing hormone (LH), prolactin (PRL), estrogens (E), and progesterone (P) in relation to the onset of reproduction, egg laying, incubation, and care of young. LH levels increase in the prelaying period, followed some days later by increased circulating levels of E, P, and PRL. Levels of these hormones tend to stabilize during egg laying with periodic ovulatory cycle changes. Around the onset of incubation PRL levels increase, while LH, E, and P levels fall. During incubation PRL reaches very high levels, falling sharply when incubation is terminated. Stimulatory effects of hypothalamic neurotransmitters, peptides, and ovarian steroids on PRL secretion have been shown. The prelaying increase is dependent on E and P and the high levels of incubation require a functional serotonergic system. The causal relationships and roles of PRL in incubation of gallinaceous birds are, however, still unclear.

The effect of ovariectomy on broodiness and plasma prolactin levels in turkey hens during a photo-induced reproductive cycle

The effects of ovariectomy on broody behavior and plasma prolactin levels were examined in turkey hens that had previous histories of broodiness. Ovariectomy eliminated all nesting behavior and blocked the photostimulated increase in plasma prolactin observed in sham-operated hens. Sham-operated hens demonstrated egg-laying patterns and nesting behavior typical of broody hens. A large increase in plasma prolactin preceded broody behavior which continued as long as the elevated amounts of plasma prolactin persisted. It was concluded that the ovary is essential in expressing broody nesting behavior, the large increase in plasma prolactin associated with this behavior, and the prolactin increase in hens that did not demonstrate nesting behavior.

Two methods for serial blood sampling from unrestrained, undisturbed turkeys with notes on the effects of acute stressors on plasma levels of prolactin

A method was developed for chronic cannulation of the atrium of the turkey. Two methods, one employing a headmount swivel-tethering system and the other a backmount swivel-tethering system, were developed for serial bleeding from cannulated turkeys kept in an environmental cubicle. To validate the methods for serial bleeding from undisturbed, unrestrained turkeys, the effects were examined of several stressors on plasma prolactin (PRL) levels in adult toms. Serial bleeding at 2-min intervals followed by withdrawal of one sample of 50 ml at 2 hr after initiation of bleeding had no effect on plasma PRL. Water deprivation for 24 hr or intraatrial infusion of hypertonic saline had no effect on plasma PRL. Intraatrial injection of 10 mg/kg of epinephrine bitartrate resulted in a significant elevation of plasma concentrations of PRL.

Influence of genetic increases in egg production on traits associated with broodiness in turkeys

Egg production, nesting frequency, and serum levels of prolactin, estradiol, and total phosphorus were monitored in relatively nonbroody (egg) and relatively broody (RBC1) strains of turkey hens during a reproductive period. In the egg strain, prolactin levels were increased in a group with a relatively high frequency of nesting in comparison to a group with a relatively low frequency of nesting. No differences between these two groups were detected for serum estradiol, total phosphorus, or egg production. In the RBC1 strain, prolactin levels did not differ between a group of hens that did not exhibit broodiness and a group that exhibited one or more bouts of broodiness. A broodiness treatment was used for the latter group. The broody group exhibited extremely variable levels of prolactin. In individual broody hens, the levels of prolactin were relatively high. After broodiness in 12 of 13 hens, the level of prolactin fell to relatively low levels. In the one hen not responding to broodiness treatment, the level of prolactin became low levels. In the one hen not responding to broodiness treatment, the level of prolactin became extremely high. Nesting frequency, total serum phosphorus, and egg production were generally not different between the two groups. The level of prolactin showed seasonal changes in both strains of hens, starting low, increasing to maximal levels between 40 and 80 days of production, and then declining to low levels late in the reproductive period. Laying hens always had higher levels of prolactin than nonlaying, nonbroody hens.

Serum levels of luteinizing hormone (LH), prolactin, estradiol, and progesterone in laying and nonlaying canvasback ducks (Aythya valisineria)

Temporal changes in the levels of serum luteinizing hormone (LH), prolactin, estradiol, and progesterone associated with the reproductive patterns of 53 wild captive canvasback ducks were measured. The reproductive endocrinology of both laying and nonlaying females was compared in this 3-year study. Females that remained sexually inactive had ovaries with small, undeveloped follicles. Nonlaying ducks also had lower serum levels of LH (P less than 0.01), prolactin (P less than 0.05), estradiol, and progesterone than those of laying ducks in mid-April (during prelay), mid-May (on the fourth day of egg production), and mid-June (during postlay and incubation). Prolactin levels of both layers and nonlayers increased over this time interval (P less than 0.01) but levels of nonlayers were significantly lower than those of layers for the three blood-sampling dates. The low prolactin levels demonstrate that reproductive failure was not a result of inhibition by high serum prolactin levels. Intravenous injections of luteinizing hormone-releasing hormone (LHRH) in female canvasbacks resulted in significantly elevated (P less than 0.01) serum LH on the prelay blood sampling date. Lack of reproduction in nonbreeding canvasbacks was thus associated with low circulating serum LH levels but with LHRH-sensitive pituitary pools. These data suggest that lack of reproduction was a result of the failure of the hypothalamus to release releasing factors. The serum hormones of laying canvasbacks varied temporally with stages of the nesting cycle. LH levels increased prior to egg laying and fluctuated during the laying period. LH levels decreased at the onset of incubation but increased after loss of clutch, with renesting activity. Serum prolactin levels of layers were low prior to egg laying and increased gradually through laying of the first clutch, the renesting period, and laying of the second clutch. The highest prolactin levels occurred in ducks incubating their eggs. Prolactin levels decreased in ducks that failed to incubate their eggs. Serum estradiol levels increased sharply between 2 and 5 weeks prior to egg laying and remained high until the second day of egg production. Estradiol levels decreased when the fourth egg was produced, and remained low through the laying of the first clutch, the renesting period, and laying of the second clutch. Progesterone fluctuated widely through the nesting cycle, showing several major peaks before laying and another during incubation.

Serum prolactin levels and crop-sac development in ring doves during a breeding cycle

Using a turkey prolactin radioimmunoassay, the serum prolactin levels of male and female ring doves (Streptopelia risoria) during the breeding cycle were measured and their circulating prolactin levels were compared to crop-sac weight on a within-bird basis. During the early phase of the incubation period, crop weight showed a delayed response to prolactin stimulation and there was no correlation; during the midincubation period when prolactin and crop-sac weight were increasing, there was a strong positive correlation; around hatching, when prolactin was at its peak, there was no correlation. There were again strong positive correlations at later samples, when squabs were developing and both prolactin and crop-sac weight were declining. Thus, it appears that the correlation between the circulating prolactin level and crop-sac development depends on the stage of the breeding cycle. While males and females showed similar pattern of circulating prolactin during the period of incubation and parental care, only females consistently showed a postovulatory rise of prolactin. These results were discussed in the context of the role of prolactin in the breeding cycle.