Effects of ovariectomy or force feeding on the plasma concentrations of prolactin and luteinizing hormone in incubating turkey hens

The effect of ovariectomy (OVX) on plasma concentrations of prolactin (PRL) and luteinizing hormone (LH) in incubating turkey hens was studied. Neither the sham-operated nor the OVX hens exhibited any change in the pattern of incubation behavior as a result of the surgery. Plasma concentrations of estradiol decreased to less than approximately 3 pg/ml by 2 days after surgery in the OVX hens. There were no significant differences in plasma levels of PRL between the sham-operated and OVX hens throughout the study. The concentration of PRL did not change in either the sham-operated or OVX hens and was maintained at high levels after surgery and during incubation of the eggs. By 2 days after hens were placed into cages, plasma levels of PRL significantly decreased and were maintained at low levels in both groups. The concentration of LH did not change in either group during the two wk after surgery when the hens were incubating eggs. After the hens were placed into cages, the concentration of LH increased in the OVX hens and was maintained at significantly higher levels than in the sham-operated hens. By contrast, the concentration of LH increased within 4 days after OVX of out-of-lay but nonincubating hens. The delay in the postcastration increase in plasma level of LH in the OVX hens was not associated with anorexia of incubating hens, since plasma levels of LH were not affected by force-feeding unless plasma levels of PRI were suppressed by nest deprivation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma prolactin levels in incubating turkey hens during pipping of the eggs and after introduction of poults into the nest

Plasma levels of prolactin (Prl) associated with incubation and maternal behavior were compared in turkey hens allowed to incubate 10 fertile eggs (Group I, n = 9) or 10 infertile eggs (Group II, n = 7) in open nest boxes. At the end of the day that the first egg hatched, all unhatched eggs were removed from Group I hens and each hen was given 10 poults. At the end of the following day, infertile eggs were removed from Group II hens and each hen was given 10 poults. Although pipping of the eggs changed the incubation behavior of Group I hens, it had no effect on plasma Prl. Subsequent hatch of the eggs and/or presence of poults resulted, within 24 h, in a sharp fall in Prl levels, abandonment of the nests, and a shift to maternal behavior. Visual and auditory exposure to Group I poults had no effect on plasma Prl or incubation behavior of Group II hens incubating infertile eggs in adjacent pens. However, within 24 h after the infertile eggs were exchanged for newly hatched poults, Prl levels in Group II hens declined sharply and the hens abandoned the nests and showed maternal behavior similar to that observed in Group I hens. No significant relationships were found in either group between plasma Prl levels and quality of incubation or maternal behavior.     

Endocrine changes in the incubating and brooding turkey hen

Turkey hens were allowed to incubate eggs and to hatch and rear young. Plasma prolactin (Prl) levels increased prior to the start of continuous incubation and rose sharply as incubation progressed to reach a peak of 1178.2 +/- 221.8 ng/ml (mean +/- SEM) just before hatching. Prl levels then fell precipitously before the hens left the nest, and returned to preincubation levels (36.8 +/- 3.4 ng/ml) by the time the poults were 2 weeks old. These results show that the high plasma concentrations of Prl found during incubation are not initiated or maintained only by the stimulus of nesting. We suggest that the decline in Prl levels at the end of incubation could be related to the pipping and hatching of eggs, and the consequent shift to maternal behavior. Plasma growth hormone (GH) levels were significantly increased in hens which were brooding poults, but not in hens incubating eggs. An elevenfold, 1-day increase in plasma GH was observed immediately after the hens left the nests. Mean plasma GH levels rose from 12.0 +/- 4.7 ng/ml on the day that the hens left the nests to 133.0 +/- 32.0 ng/ml on the following day, and then declined to 23.1 +/- 9.6 ng/ml after an additional day. There were no significant changes in plasma thyroxine levels during laying, incubation and brooding. Plasma glucose concentration was significantly depressed during incubation.     

Influence of Nest Deprivation on Behaviour,Hormonal Concentrations and on the Ability to Resume Incubation in Domestic Hens (Gallus domesticus)

In this study, we investigated the influence of the length of nest deprivation period (3 vs. 6 d) on the ability to renest of incubating hens. We focused on the hens' behaviour, particularly on nesting and calls, on their prolactin, luteinizing hormone (LH) and oestradiol concentrations. Nest deprivation induced a drop of prolactin and an increase of LH plasmatic concentrations in hens. These changes in circulating pituitary hormones were followed by changes in ovarian function: the persistent rise of plasmatic oestradiol gave evidence of the resumption of ovarian activity. After nest deprivation, the number of clucks increased significantly and food calls appeared; these results demonstrate that ‘maternal’ calls can be emitted outside the maternal context. Our results suggest that the onset of typical maternal calling is strongly controlled by internal state such as plasmatic hormonal concentrations, independently of social stimulation. None of the 10 hens deprived for 6 d resumed incubation when given the opportunity, whereas, after a 3 d deprivation period, three out of 10 hens renested and two hens incubated sporadically and then gradually abandoned their nests. Long periods of nest deprivation appear to disrupt the habits of sitting and nesting. Before nest reopening, all the hens presented low levels of plasmatic prolactin. Plasma prolactin concentrations of the renesting hens increased after nest boxes were reopened and returned to levels found in incubating hens. We suggest that pituitary prolactin rather than plasmatic prolactin is responsible for the maintenance of incubating potential in hens deprived of their nests.     

Reinitiation of ovulatory cycles in incubating female turkeys by an inhibitor of serotonin synthesis, P-chlorophenylalanine

Nest deprivation of incubating turkeys caused a decrease in serum prolactin (Prl) levels from 1184.5 +/- 116.4 ng/ml to 896.8 +/- 83.0 ng/ml 1 day after initiation of deprivation, with a further decline to 156.5 +/- 111.7 ng/ml at the end of the 22-day experimental period. Serum luteinizing hormone (LH), progesterone and estradiol levels following nest deprivation were similar to those in birds allowed to incubate (controls). Oral administration of p-chlorophenylalanine (PCPA, 50 mg/kg) to incubating turkeys for 3 consecutive days reduced nesting frequency (P less than 0.05) on the 4th day after initiation of treatment and the nesting virtually ceased by the 9th day. Pretreatment Prl was 1655 +/- 210 ng/ml and declined (P less than 0.05) after PCPA administration to a low of 28.6 +/- 2.8 ng/ml. In addition, PCPA caused a sustained rise in serum LH peaking (5.59 +/- 1.09 ng/ml) 3 days after treatment initiation. Contrary to nest deprivation, serum levels of progesterone and estradiol increased (P less than 0.05) as a consequence of PCPA treatment. Seven of 8 PCPA-treated birds later came into lay when their Prl levels and nesting frequency increased again. The results suggest a role for serotonin (5-HT) in incubation behavior, and Prl and LH secretion in turkeys.     

Effects of preoptic and hypothalamic lesions in female turkeys during a photoinduced reproductive cycle

Prolactin (Prl) is released by electrical stimulation in the turkey hypothalamus and preoptic area (POA). Possible trajectories for POA efferents to the median eminence (ME) were tested by placing lesions in the POA, the lateral hypothalamus (LHy), or the ventromedial nucleus of the hypothalamus (VMN) of reproductively quiescent turkey hens, then subjecting them to long photoperiods while monitoring their blood Prl levels and nesting activities. In addition, lesions were made in the VMN of a group of incubating hens to learn whether the lesions would cause the elevated Prl levels to fall or interfere with incubation behavior. Lesions in medial POA, LHy, or VMN prevented the onset of incubation and prevented the large rise in Prl associated with it. However, these lesions did not interfere with the initial, more gradual Prl rise caused by increasing daylengths. Lesions in LHy or VMN appeared to interfere with a pathway lying laterally from POA to ME. Electrical stimulation in medial POA, which caused an increase in circulating Prl, failed to do so in hens with LHy or VMN lesions. Lesions in the VMN of incubating hens caused them to leave the nest and suffer a large decline in Prl, both within 48 h. It is tentatively suggested that incubation behavior and its associated elevated Prl are prevented by the POA lesions and that lesions in LHy or VMN, which mimic POA lesion effects, interfere with POA efferents projecting to ME.     

Ovarian steroid production in vitro during gonadal regression in the turkey. I. Changes associated with incubation behavior.

The mechanism regulating ovarian regression during incubation behavior in the domestic turkey has not been elucidated. This study was designed to determine whether ovarian steroidogenic potential is depressed during gonadal regression associated with the onset of incubation behavior. Hens were housed in floor pens equipped with trap nests that were checked 7 times per day. Hens were grouped, according to nesting frequency and egg production, into the following classifications: laying (laid an egg every day and trapped in the nest only once/day); transitional (laid an egg every day but trapped in the nest 4 or more times/day); and Day 1, Day 3, and Day 5 incubating (no egg for 2, 4, or 6 days, respectively, while trapped in the nest at least 4 times/day). Follicular atresia was evident in the largest preovulatory follicle (F1) in transitional hens, extensive in F1 through the third largest follicle (F3) in Day 1 incubating hens, and extensive in F1 through F7in Day 3 incubating hens. Levels of circulating LH, progesterone (P), androgen (A), and estradiol (E) decreased in transitional hens relative to concentrations in laying hens and remained low thereafter. In contrast, levels of prolactin were greater in Day 3 and Day 5 incubating hens than in laying, transitional, or Day 1 incubating hens. Basal production of P by F1 granulosa cells was lower from Day 1 incubating hens than from the other groups. Production of P in response to porcine-luteinizing hormone (pLH) was greater by cells from transitional and Day 1 incubating hens than from those of laying hens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intracranial prolactin perfusion induces incubation behavior in turkey hens

Intracranial perfusion of ovine prolactin (oPrl) via osmotic pump in laying turkey hens caused a sudden onset in incubation behavior, defined as an increase in nest visits. The hens also displayed a gradual decrease in egg laying during the time they were receiving oPrl, another indicator of the onset of incubation. Circulating immunoreactive turkey Prl levels fell during the perfusion period, even though the hens were displaying persistent nesting activity and reduced egg laying. No effects on serum LH were noted. Perfusion of oPrl during the first 14 days of photostimulation delayed the onset of egg laying by several days. No effects on serum Prl or serum LH were noted. It is suggested that incubation behavior is facilitated by central levels of Prl.     

Effect of turkey (Meleagridis gallopavo) breeder hen age and egg size on poult development. 1. Intestinal growth and glucose tolerance of the turkey poult

Three experiments were conducted to determine if turkey (Meleagridis gallopavo) hen age and egg weight affect poult intestinal development and glucose tolerance during the first week after hatching. Differences in glucose tolerance were not consistent across the experiments. In experiment 1, 4-day-old poults from the younger hens and lightest egg weight class had significantly greater fasting plasma glucose concentrations (P<0.04) and were also higher at 30 and 60 min post-injection of 250 mg glucose. In experiment 2, egg weight class had no significant effects on plasma glucose concentrations of 4-day-old poults (after injection of 2.5 mg glucose/g body weight). In experiment 3, plasma glucose concentrations were not different between groups at 0 or 30 min post-injection (3.75 mg glucose/g body weight), however, poults from the younger hens had 79–90 mg/dl higher plasma glucose concentrations 60 min post-injection versus poults from the older hens. Neither egg weight class or hen age consistently affected small intestinal weight, length, or density (g/cm) measures across experiments.     

Endocrinological and behavioural effects of p-chlorophenylalanine (PCPA) oral administration to broody turkey hens (Meleagris gallopavo)

Changes in plasma levels of prolactin and LH, feed intake, water consumption, behavioural pattern and ovarian activity were recorded after oral administration of PCPA to broody turkey hens. A decrease in prolactin concentration was measured, from day 3, in 3 out of the 5 birds treated with 100 mg PCPA/kg body weight (BW) for 3 consecutive days. In these hens, broodiness was disrupted on day 6 and feeding activity subsequently increased to levels of photorefractory hens. Neither LH concentrations nor ovarian activity were affected after treatment with PCPA. Moreover, PCPA treatment was ineffective at a 50 mg/kg BW dose. These results confirm that a serotoninergic mechanism is probably involved in prolactin release and moreover suggest that prolactin is implicated in maintaining broody behaviour. However, the reductions in the plasma concentration of prolactin induced by PCPA were not sufficient to restore the hypothalamic-hypophyseal-ovarian axis to a physiological status characteristic of the laying hen. Therefore, PCPA does not appear to be a useful method of treating broodiness in commercial turkey hens.     

Factors influencing productivity of eastern wild turkeys in northeastern South Dakota

Population growth is highly sensitive to changes in reproductive rates for many avian species. Understanding how reproductive rates are related to environmental conditions can give managers insight into factors contributing to population change. Harvest trends of eastern wild turkey in northeastern South Dakota suggest a decline in abundance. We investigated factors influencing reproductive success of this important game bird to identify potential factors contributing to the decline. We monitored nesting rate, nest survival, renesting rate, clutch size, hatchability, and poult survival of 116 eastern wild turkey hens using VHF radio transmitters during the springs and summers of 2017 and 2018. Heavier hens were more likely to attempt to nest than lighter hens, and adult hens were more likely to renest than yearling hens. Nest survival probability was lowest in agricultural fields relative to all other cover types and positively related to horizontal visual obstruction and distance to the nearest road. Daily nest survival probability demonstrated an interaction between temperature and precipitation, such that nest survival probability was lower on warm, wet days, but lowest on dry days. Egg predation was the leading cause of nest failure, followed by haying of the nest bowl and death of the incubating hen. Poults reared by adult hens had a greater probability of survival than poults reared by yearling hens. Our estimate of survival probability of poults raised by yearling hens was low relative to other studies, which may be contributing to the apparent regional population decline. However, there is little managers can do to influence poult survival in yearling hens. Alternatively, we found nest survival probability was lowest for nests initiated in agricultural fields. Wildlife‐friendly harvesting practices such as delayed haying or installation of flushing bars could help increase productivity of eastern wild turkey in northeastern South Dakota.     

Increased proliferative activity and programmed cellular death in the turkey hen pituitary gland following interruption of incubation behavior

Incubation behavior or broodiness in turkey hens is characterized by ovarian regression, hyperprolactinemia, and persistent nesting. Nest-deprivation of incubating turkey hens results in disruption of broodiness accompanied by a precipitous decline in plasma prolactin (PRL) concentrations. The objective of the present study is to examine cellular changes in the pituitary gland associated with nest-deprivation for 0, 1, 2, 3, 4, or 7 days. Bromodeoxyuridine (BrdU) was administered prior to kill to study proliferative activity. Pituitary tissue sections were immunostained using turkey growth hormone (GH) antibody, and/or chicken PRL peptide antibody, and BrdU antibody. Plasma PRL concentrations declined significantly following nest-deprivation for 1 or more days. The midsagittal pituitary area immunoreactive (ir) to GH was significantly increased while that of PRL was significantly decreased following nest-deprivation for 2 or more days. Terminal deoxy-UTP nick end labeling and PRL-immunostaining revealed an abundance of apoptotic nuclei in both cephalic and caudal lobes of the anterior pituitary gland, suggestive of programmed cellular death of lactotrophs in the pituitary gland of hens nest-deprived for 2 or more days. Mammosomatotrophs were abundant in hens nest-deprived on Day 0 but were absent in hens nest-deprived for 1 or more days. Proliferating (BrdU-ir) cells were significantly abundant in the pituitary cephalic and caudal lobes following nest-deprivation for 1 or more days but were absent on Day 0 or in laying hens. Dual-labeling studies indicated that most of the BrdU-ir nuclei in the caudal lobe were not colocalized in somatotrophs in hens nest-deprived for 1-4 days but did colocalize with GH following 7 days of nest-deprivation. In conclusion, nest-deprivation of incubating turkey hens results in 1) a precipitous decline in plasma PRL concentration, 2) programmed cell death of lactotrophs, 3) disappearance of mammosomatotrophs, 4) increased proliferative activity of pituitary cells, and 5) recruitment of somatotrophs arising primarily from mitosis of nonsomatotrophic cells.     

Hormonal induction of incubation behavior in ovariectomized female turkeys (Meleagris gallopavo)

Two experiments were conducted to evaluate the effect of estradiol benzoate (EB), progesterone (P), ovine prolactin (oPrl), or their combinations on temporal patterns of serum luteinizing hormone (LH) and Prl and on nesting behavior in adult ovariectomized female turkeys. Levels of serum LH were initially reduced (p greater than 0.05) by the steroid treatments, while continuation of treatments induced surges of LH to levels comparable to pretreatment levels. Administration of steroid increased (p less than 0.05) levels of serum Prl, which persisted until termination of treatments. Administration of oPrl had no effect on levels of serum LH but blunted the steroid-induced release of Prl. Neither EB, P, nor oPrl treatments alone nor a combination of EB + P elicited nest occupation. Nest occupation was observed after administration of P only in turkeys pretreated with EB. Administration of oPrl maintained and advanced the P-induced nesting to persistent nesting behavior (incubation behavior). Once persistent nesting behavior was established, hormonal treatments were terminated, yet nesting behavior was maintained and serum samples showed increasing levels of Prl and decreasing levels of LH. It is suggested that incubation behavior in the female turkey is facilitated by the combined action of estradiol, P, and Prl.     

Cytosolic progesterone receptors in the oviducts of reproductively active and quiescent turkeys (Meleagris gallopavo)

Cytosolic progesterone receptors (PRcs) from the reproductive tract of the female turkey were analyzed by high-performance liquid chromatography using a diethylaminoethyl (DEAE) ion-exchange column. PRcs from oviduct tissue of laying, incubating, photorefractory and short-day turkey hens were compared. In general, three types of PRcs were identified: Receptor I, a partially displaceable species that was eluted at a 0.13 M salt concentration; and Receptors II and III, which were two specific binding species eluting at 0.23 M and 0.26 M, respectively. In the subdivided tissue from the laying hen oviduct, Receptor I was the major PRc species of the isthmus and Receptor III was the only receptor present in the uterus. The infundibulum and magnum each contained a small amount of Receptor II and a substantial amount of Receptor III. The whole oviduct of incubating hens contained a greater proportion of Receptor I than Receptor II or III, and these last two receptor types were present in equal quantity. The whole oviduct of the short-day hens had an equal distribution of the three receptor types. In the presence of sodium molybdate, an inhibitor of phosphatase and protease, only one sharp Receptor II species was seen in the magnum and uterus of the laying hen oviduct and in the whole oviducts of incubating and short-day hens. The transformation of Receptor II to Receptor III in the absence of sodium molybdate was facilitated by the aging of cytosol at 0-4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 5(th) and the 10(th) 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.     

Pituitary luteinizing hormone and prolactin messenger ribonucleic acid levels are inversely related in laying and incubating turkey hens.

The relationships of prolactin (PRL) and LH messenger (m) RNA to serum and pituitary content were determined for turkey hens at different phases of the reproductive cycle. In the nonphotostimulated, reproductively inactive hen, serum and pituitary PRL content and pituitary PRL mRNA levels were low. All three PRL values rose after photostimulation and peaked during the incubation phase. Relative to nonphotostimulated hens, hyperprolactinemic incubating hens showed 220-, 11-, and 57-fold increases in serum PRL, pituitary PRL content, and pituitary PRL mRNA levels, respectively. These peak levels declined 80-, 3-, and 6-fold, respectively, in photorefractory hens. In contrast to PRL levels, serum LH, pituitary LH, and pituitary LH beta-subunit mRNA levels did not change as dramatically. Serum LH showed no significant changes for the different reproductive phases. Pituitary LH peaked after photostimulation and declined to its lowest level in incubating hens. Pituitary LH-beta mRNA abundance was highest in photostimulated and laying hens and lowest in incubating and photorefractory hens. These results demonstrate that the abundance of LH-beta and PRL mRNA shows an inverse relationship in photostimulated/laying and incubating turkey hens.     

Effects of dietary chromium and zinc on egg production, egg quality, and some blood metabolites of laying hens reared under low ambient temperature

This experiment was conducted to evaluate the effects of chromium (chromium picolinate, CrPic) and zinc (ZnSO₄·H₂O) on egg production, egg quality, and serum insulin, corticosterone, glucose, cholesterol, and total protein concentrations of laying hens reared under a low ambient temperature (6.8°C). One hundred twenty laying hens (Hy-Line; 32 wk old) were divided into 4 groups, 30 hens per group. The laying hens were fed the control diet (T1) or the control diet supplemented with either 400 μg of Cr/kg of diet (T2), 30 mg of Zn/kg of diet (T3), or 400 μg of Cr plus 30 mg of Zn/kg of diet (T4). Although the dry matter intake (DMI) was similar (p>0.05) for all treatment groups, supplemental chromium and zinc either individually or together increased live-weight change, egg production, and improved feed efficiency (p<0.05). However, no significant differences were observed between T4 and T2 or T3. Compared to T1, supplemental chromium and zinc increased egg weight, eggshell weight, eggshell thickness, egg specific gravity, and Haugh unit (p<0.05) in T2, T3, and T4 groups, among which there was no significant difference. Serum insulin concentration increased (p<0.05) and corticosterone concentration decreased (p<0.05) with dietary chromium and zinc supplementation. Serum glucose and cholesterol concentrations decreased (p<0.05) and protein concentrations increased (p<0.001) with dietary chromium and zinc supplementation in all treatment groups. The results of this study indicated that either supplemental dietary chromium or zinc increased plasma insulin and decreased corticosterone concentrations and that had a positive effect on performance of laying hens under low ambient temperature.     

Production of corticosterone in male homozygous Brattleboro rats

Plasma concentration, metabolic clearance rate and in vitro adrenal production of corticosterone were measured in Brattleboro male rats homozygous for diabetes insipidus (DI) and in Long-Evans male rats (LE) as controls in resting conditions, under stress caused by pentobarbitone anesthesia and surgery and after three days water deprivation. In resting animals, plasma concentrations and in vitro adrenal production of corticosterone were higher in DI rats than in LE rats. Under pentobarbitone anesthesia and surgery, plasma concentrations and metabolic clearance rate of corticosterone were slightly but not statistically lower in DI rats; however, the in vivo production rate of corticosterone was significantly lower. After three days water deprivation, increasing plasma corticosterone level was consistently higher in DI than in Le rats. These results are not in favour of a reduced glucocorticoid activity of the adrenal of DI rats and of an important role played by vasopressin on the stimulation of the hypothalamopituitary adrenal activity at least in resting conditions; its role may depend upon stressful circumstances.     

Thwarting of behaviour in different contexts and the gakel-call in the laying hen

Earlier studies have shown that thwarting of feeding behaviour in the laying hen is expressed through a specific vocalisation, the gakel-call. The first aim of this study was to investigate whether the effect of deprivation per se on the occurrence of gakel-calls can be distinguished from the effect of the additional frustration. Frustration is defined as the state of an animal that results from nonreward in the expectancy of reward. The second aim was to investigate whether the occurrence of gakel-calls is restricted to a food context or whether it can be regarded as an expression of frustration in general. For this purpose, 20 hens were deprived of food, water and dustbath. After deprivation at a fixed time, a cue was given and the hens were rewarded with access to food, water or dust during a 15-min session on 4 consecutive days. On the fifth day, they were thwarted in the associated behaviours by blocking the access to these commodities, after the hens had been presented the signal that previously preceded the reward. We then recorded behaviours that might reflect the state of frustration in three 15-min periods. The period "Pre-Frustration" started 15 min before "Frustration". This, in turn, was followed by the period "Post-frustration" in which the hens were rewarded again. Nesting behaviour was thwarted by blocking the access to the nest (Frustration) after a hen had reached the last stage of its prelaying behaviour.In the food, water and dustbath context, deprivation elicited gakel-calls. The additional frustration resulted in a higher number of gakel-calls in all contexts except the food context. However, together with the findings of previous experiments, the results of this study suggest that frustration, in general, is expressed through the gakel-call. Frustration in the nest context elicited more gakel-calls than the other contexts. This latter finding is discussed in the light of the occurrence of the gakel-call under natural circumstances.     

Exogenous prolactin delays photo-induced sexual maturity and suppresses ovariectomy-induced luteinizing hormone secretion in the turkey (Meleagris gallopavo)

A direct effect of prolactin (Prl) on gonadotropin secretion has been suggested but not convincingly demonstrated. The secretion of LH in response to photostimulation (phs) and ovariectomy (ovx) was evaluated in adult female turkeys that had received injections of ovine Prl (124 IU/bird/day for 14 days). In experiment 1, oPrl administration initiated on the day of ovx and phs in reproductively quiescent birds suppressed (p less than 0.05) the elevated LH from a peak level of 11.7 +/- 3.5 ng/ml to 5.1 +/- 0.8 ng/ml in ovx hens. The photo-induced LH increase was unaffected by the oPrl treatment in intact birds. In experiment 2, the oPrl treatment was initiated 7 days before ovx and/or phs. This treatment blunted the peak increase in LH level that follows phs in intact (p less than 0.05) and in ovx (p less than 0.05) hens. In both experiments, onset of lay following phs was delayed (p less than 0.05) in the oPrl-treated groups (29.4 +/- 0.9 days vs. 22.3 +/- 0.9 days; 34.8 +/- 0.5 days vs. 25.0 +/- 0.9 days). In experiment 3, administration of oPrl after ovx of laying hens suppressed the LH rise at essentially all sampling times tested. At the end of the experimental period, 6 of the 7 sham-operated, oPrl-treated laying hens, but none of the sham controls, displayed incubation behavior and had Prl levels of 1020 +/- 370 ng/ml compared to 34 +/- 7 ng/ml in vehicle-treated controls. The results suggest a role for Prl in incubation behavior and LH secretion in the turkey.