Effects of age, sex, and ascorbic acid ingestion on chicken plasma corticosterone levels

Evidence for progesterone acting as an inhibitor of stress axis via stimulating pituitary neuropeptide B/W receptor 2 (NPBWR2) expression in chickens

In vertebrates, the hypothalamus-pituitary-adrenal gland (HPA) axis is the main endocrine pathway regulating the stress response, thus also called the stress axis. It has been well-accepted that the stress axis is tightly controlled by both hypothalamic stimulators and inhibitors [e.g. corticotropin (ACTH)-releasing inhibitory factor (CRIF)]. However, the identity of authentic CRIF remains unclear for decades. Recently, neuropeptide W (NPW) was proved to be the physiological CRIF in chickens. Together with its functional receptor (NPBWR2), they play critical roles in attenuating the activity of the chicken stress axis. Because increasing pieces of evidence suggested that sex steroids could regulate the stress axis, using chicken as a model, we investigated whether the newly identified CRIF and its receptor are under the control of sex steroids in this study. Our results showed that: (1) expression of NPW-NPBWR2 in the hypothalamus-pituitary axis was sexually dimorphic and developmental stage-dependent; (2) progesterone (P₄), rather than 17β-estradiol (E₂) and dihydrotestosterone (DHT), could dose- and time-dependently upregulate NPBWR2 expression, which was accompanied with the decrease of ACTH synthesis and secretion, in cultured pituitary cells; (3) intraperitoneal injection of P₄ could elevate the mRNA level of pituitary NPBWR2; (4) P₄-stimulated NPBWR2 expression was relevant to both nPR-mediated genomic action and mPRs-triggered nongenomic route associated with MEK/ERK, PI3K/AKT cascade, and calcium influx. To our knowledge, our results discover a novel route of sex steroids in modulating the stress axis of chickens, which lays a foundation to reveal the complicated interaction network between reproduction and stress axes in chickens.

Evaluation of mechanical cervical dislocation, captive bolt, carbon dioxide, and electrical methods for individual on-farm euthanasia of broiler breeders

Efficacious euthanasia by applying manual cervical dislocation can be difficult on large and mature poultry. The challenge with using manual cervical dislocation is that the strength required to hold heavy poultry and swiftly apply cervical dislocation can be physically impossible for most people. Therefore, alternative methods of euthanasia are needed for mature and large poultry. Mechanical cervical dislocation using the Koechner Euthanizing Device (KED), captive bolt using the Turkey Euthanasia Device (TED), carbon dioxide (CO₂), and electrical euthanasia were evaluated for use on 65-wk-old broiler breeders at flock termination. Following application of each method, physiological reflexes including the eye nictitating membrane reflex, mouth gaping, and body movement, broken skin, blood loss, kill success, time to cessation of heartbeat, and blood plasma corticosterone levels were assessed. Birds euthanized using the KED had longer response durations for eye nictitating membrane (91 s) and reflexive mouth gaping (161 s) compared to TED, CO₂, and electrical euthanasia (0–7 s). Body movement durations were also longer for KED (214 s) and TED (209 s) than for CO₂ and electrical euthanasia (0–8 s). The highest percentages of broken skin (93%) and blood loss (96%) were observed for TED, followed by KED (71%, 68%), then CO₂ (0%, 6%) and electrical euthanasia (0%, 3%). No significant differences (P = 0.1781) were observed for kill success rates with 98% for KED, 100% for TED, 97% for CO₂, and 100% for electrical euthanasia at 4-min. Time to heartbeat cessation did not differ between KED (659 s), TED (427 s), or CO₂ (583 s) euthanasia methods. No heartbeat was detected following electrical euthanasia. Blood plasma corticosterone levels did not differ between preeuthanasia or posteuthanasia from any of the methods applied. Based on these results each euthanasia method is acceptable for use with broiler breeders.

Effects of genetic selection on activity of corticotropic and thyrotropic axes in modern broiler chickens

Commercial selection for meat-type (broiler) chickens has produced economically valuable birds with fast growth rates, enhanced muscle mass, and highly efficient feed utilization. The physiological changes that account for this improvement and unintended consequences associated with them remain largely unexplored, despite their potential to guide further advancements in broiler production efficiency. To identify effects of genetic selection on hormonal signaling in the adrenocorticotropic and thyrotropic axes, gene expression in muscle and liver and post-hatch circulating hormone concentrations were measured in legacy [Athens Canadian Random Bred (ACRB)] and modern (Ross 308) male broilers between embryonic days (e) 10 and e18 and post-hatch days (d) 10 and d40. No interactive effects or main effects of line were observed for adrenocorticotropic gene expression during either developmental period, although age effects appeared for corticosteroid-binding globulin in liver during embryogenesis and post-hatch and glucocorticoid receptor in both tissues post-hatch. There was a main line effect for circulating corticosterone, with levels in ACRB greater than those in Ross. Several thyrotropic genes exhibited line-by-age interactions during embryonic or post-hatch development. In liver, embryonic expression of thyroid hormone receptor beta was greater in ACRB on e12, and deiodinase 3 (DIO3) levels were greater in Ross on e14 and e16. In juvenile liver, deiodinase 2 (DIO2) expression was greater in ACRB on d10 but greater in Ross on d20, while DIO3 was higher in ACRB on d30 and d40. Levels of thyroid hormone receptor alpha mRNA exhibited a main line effect, with levels greater in ACRB juvenile breast muscle. Several thyrotropic genes exhibited main age effects, including DIO2 and DIO3 in embryonic breast muscle, thyroid hormone receptor alpha and thyroid hormone receptor beta in post-hatch liver, and DIO2 in post-hatch breast muscle. Circulating triiodothyronine displayed a main line effect, with levels in Ross significantly reduced as compared to ACRB. These findings suggest that in modern broilers, a decrease in levels of hormones that control basal metabolism triiodothyronine and the stress response circulating corticosterone, as well as altered expression of genes regulating thyroid hormone activity, could contribute to lower heat production, reduced stress response, and altered nutrient partitioning, leading to more efficient feed utilization and faster, more productive growth.

Corticosterone Metabolite Concentration Is Not Related to Problem Solving in the Fawn-Footed Mosaic-Tailed Rat Melomys Cervinipes

Animals can respond physiologically, such as by adjusting glucocorticoid hormone concentrations, to sudden environmental challenges. These physiological changes can then affect behavioural and cognitive responses. While the relationships between adrenocortical activity and behaviour and cognition are well documented, results are equivocal, suggesting species-specific responses. We investigated whether adrenocortical activity, measured using corticosterone metabolite concentration, was related to problem solving in an Australian rodent, the fawn-footed mosaic-tailed rat (Melomys cervinipes). Mosaic-tailed rats live in complex environments that are prone to disturbance, suggesting a potential need to solve novel problems, and have been found to show relationships between physiology and other behaviours. We measured problem solving using five food-baited puzzles (matchbox and cylinder in the home cage, and activity board with pillars to push, tiles to slide and levers to lift in an open field), and an escape-motivated obstruction task in a light/dark box. Faecal samples were collected from individuals during routine cage cleaning. Adrenocortical activity was evaluated non-invasively by measuring faecal corticosterone metabolites using an enzyme immunoassay, which was biochemically and biologically validated. Despite varying over time, adrenocortical activity was not significantly related to problem solving success or time spent interacting for any task. However, as adrenocortical activity is reflective of multiple physiological processes, including stress and metabolism, future studies should consider how other measures of physiology are also linked to problem solving.

Differential delayed responses of arginine vasotocin and its receptors in septo-hypothalamic brain structures and anterior pituitary that sustain hypothalamic-pituitary-adrenal (HPA) axis functions during acute stress

Recently, we proposed that corticotropin releasing hormone (CRH) neurons in the nucleus of hippocampal commissure (NHpC), located in the septum, function as a part of the traditional hypothalamic-pituitary-adrenal (HPA) axis in avian species. CRH and its receptor, CRHR1, are regulated differently in the NHpC compared to the paraventricular nucleus (PVN) following feed deprivation (FD). Therefore, we followed up our work by examining arginine vasotocin (AVT), the other major ACTH secretagogue, and its receptors, V1aR and V1bR, gene expression during FD stress in the NHpC, PVN, and ventral mediobasal hypothalamus/median eminence (MBHv/ME). The objectives were to 1) identify AVT perikarya, fibers and its two major receptors, V1aR and V1bR, in the NHpC, PVN, and MBHv/ME using immunohistochemistry, 2) determine the effect of stress on AVT, V1aR and V1bR mRNA expression in the same three brain structures, NHpC, PVN, and MBHv/ME; and, 3) ascertain the expression pattern of V1aR and V1bR mRNA in the anterior pituitary and measure plasma stress hormone, corticosterone (CORT), concentration following FD stress. Male chicks (Cobb 500), 14 days of age, were divided into six groups (10 birds/treatment) and subjected to different times of FD stress: (Control, 1 h, 2 h, 3 h, 4 h, and 8 h). For each bird, blood, brain, and anterior pituitary were sampled and frozen immediately. The NHpC, PVN, and MBHv/ME were micro-dissected for RT-PCR. Data were analyzed using one-way ANOVA followed by Tukey Kramer HSD test using a significance level of p < 0.05. Perikarya of AVT neurons were identified in the PVN but not in the NHpC nor MBHv/ME, and only V1aR-immunoreactivity (ir) was observed in the three structures, however, gene expression data for AVT and its two receptors were obtained in all structures. Both AVT and V1aR mRNA are expressed and increased significantly in the PVN following FD stress (p < 0.01). For the first time, V1bR mRNA was documented in the avian brain and specifically shown upregulated in the NHpC and PVN (p < 0.01) following stress. Additionally, delayed significant gene expression of AVT and its receptors in the PVN showed a positive feedback relationship responsible for maintaining CORT release. In contrast, a significant downregulation of AVT mRNA and upregulation of V1aR mRNA occurred in the NHpC (p < 0.01) during FD showing a negative feedback relationship between AVT and its receptors, V1aR and V1bR. Within the MBHv/ME and anterior pituitary, a gradual increase of AVT mRNA in PVN as well as MBHv/ME was associated with significant upregulation of V1bR (p < 0. 01) and downregulation of V1aR (p < 0.01) in both MBHv/ME and anterior pituitary indicating AVT regulates its receptors differentially to sustain CORT release and control overstimulation of the anterior pituitary during a stress response.

No evidence for sex-specific effects of the maternal social environment on offspring development in Japanese quail (Coturnix japonica)

The social environment of reproducing females can cause physiological changes, with consequences for reproductive investment and offspring development. These prenatal maternal effects are often found to be sex-specific and may have evolved as adaptations, maximizing fitness of male and female offspring for their future environment. Female hormone levels during reproduction are considered a potential mechanism regulating sex allocation in vertebrates: high maternal androgens have repeatedly been linked to increased investment in sons, whereas high glucocorticoid levels are usually related to increased investment in daughters. However, results are not consistent across studies and therefore still inconclusive. In Japanese quail (Coturnix japonica), we previously found that pair-housed females had higher plasma androgen levels and tended to have higher plasma corticosterone levels than group-housed females. In the current study we investigate whether these differences in maternal social environment and physiology affect offspring sex allocation and physiology. Counter to our expectations, we find no effects of the maternal social environment on offspring sex ratio, sex-specific mortality, growth, circulating androgen or corticosterone levels. Also, maternal corticosterone or androgen levels do not correlate with offspring sex ratio or mortality. The social environment during reproduction therefore does not necessarily modify sex allocation and offspring physiology, even if it causes differences in maternal physiology. We propose that maternal effects of the social environment strongly depend upon the type of social stimuli and the timing of changes in the social environment and hormones with respect to the reproductive cycle and meiosis.

Transgenerational effects of early experience on behavioral, hormonal and gene expression responses to acute stress in the precocial chicken

Stress during early life can profoundly influence an individual's phenotype. Effects can manifest in the short-term as well as later in life and even in subsequent generations. Transgenerational effects of stress are potentially mediated via modulation of the hypothalamic-pituitary-adrenal axis (HPA) as well as epigenetic mechanisms causing heritable changes in gene expression. To investigate these pathways we subjected domestic chicken (Gallus gallus) to intermittent social isolation for the first three weeks of life. The early life stress resulted in a dampened corticosterone response to restraint stress in affected birds and in their male offspring. Stress-specific genes, such as early growth response 1 (EGR1) and corticotropin releasing hormone receptor 1 (CRHR1), were upregulated immediately after restraint stress, but not under baseline conditions. Treatment differences in gene expression were also correlated across generations which indicate transgenerational epigenetic inheritance. In an associative learning test early stressed birds made more correct choices suggesting a higher coping ability in stressful situations. This study is the first to show transgenerational effects of early life stress in a precocial species by combining behavioral, endocrinological, and transcriptomic measurements.

Sex differences in plasma corticosterone release in undisturbed chickens (Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

In birds, two neuropeptides, corticotropin releasing hormone (CRH) and arginine vasotocin (AVT), are major regulators of the hypothalamo-pituitary-adrenal axis (HPA) during the stress response. In birds, however, the relative efficacy of CRH and AVT to stimulate the HPA axis in males and females remains unknown. The purpose of this study was to determine the time course of CORT release following central CRH and AVT administration to male and female chickens. Chickens were fitted with a stainless steel cannula surgically implanted in the lateral ventricle and a catheter chronically inserted in the jugular vein. Birds were housed individually in cages behind a one-way glass partition and unnecessary noise was avoided during the sampling period. Each bird received a single 5.0microtracerebroventricular (ICV) injection of either saline (SAL), AVT (10 and 100pmol), or CRH (10 and 100pmol). Blood was sampled remotely every 15min for 2h and plasma CORT was determined by radioimmunoassay. There was a significant increase in plasma CORT concentration in males injected with 100pmol AVT beginning at 15min post-injection through 2h compared with SAL injected birds. In males, injection of 100pmol CRH was significantly more effective in releasing CORT compared to an equal molar concentration of AVT or SAL. In females, ICV injection of 100pmol AVT induced moderate increase in CORT levels. In contrast, 100pmol CRH significantly increased plasma CORT compared to SAL injected controls but the CORT response was nearly 50% less than that obtained in males.

Relationship between hypothalamic-pituitary-adrenal axis responsiveness and age, sexual maturity status, and sex in Japanese quail selected for long or short duration of tonic immobility

The influences of age (4 to 12 wk), sexual maturity status, and sex on hypothalamic-pituitary-adrenal (HPA) axis responsiveness were investigated by measuring changes in peripheral basal levels of corticosterone (B) and responses to 10 min of physical restraint in a crush cage or injection of 1-24 adrenocorticotropic hormone (ACTH) in 2 genotypes of Japanese quail divergently selected for long (LTI) or short (STI) duration of tonic immobility (TI). Although gonad development was more advanced in male STI quail, most birds were still immature at 4 wk of age, but sexual maturity was fully acquired by 6 wk of age in both sexes and genotypes. This change was associated with increases in basal B levels in both genotypes and sexes. On the other hand, HPA axis responsiveness to restraint and adrenal responsiveness to 1-24 ACTH injection remained stable in STI quail, whatever the age. Conversely, significant responses to restraint compared with basal B levels were only observed at 4 and 6 wk of age, and adrenal responsiveness increased with age in LTI quail. Moreover, higher B levels were measured in response to restraint in STI than in LTI quail, whereas similar adrenal responses were measured at 9 and 12 wk of age. We concluded that an increase in basal B levels is associated with the stage of sexual maturity acquired, but it did not affect HPA axis responsiveness or adrenal B response capacity. On the other hand, age affected HPA axis responsiveness and adrenal B response capacity in LTI quail of both sexes but not in STI quail. It is hypothesized that functional HPA axis maturity occurs after 6 wk of age in the LTI genotype, but it is reached by 4 wk of age in the STI genotype. In conclusion, the divergent selection program for TI conducted on quail resulted in changes in HPA responsiveness that probably resulted from differences in development rate and function of the adrenal glands or other upstream structures of the HPA axis.

Episodic Gonadotropin Secretion in the Mature Fowl: Serial Blood Sampling from Unrestrained Male Broiler Breeders (Gallus domesticus)1

Forty-week-old male broiler breeders were used in two experiments. Males were reared as recommended by the breeder, housed in individual cages, and cannulated to facilitate blood sampling. In experiment 1, blood samples were collected at 10- min intervals for 4 h commencing the day of cannulation (Day 0) and for 12 h on each of Days 1 and 2. In experiment 2, blood samples were collected at 10-min intervals for 8 h on Day 1. After centrifugation, plasma was stored at -20 degrees C until LH, FSH (experiment 1 and 2), testosterone, and corticosterone (experiment 1) concentrations were determined by RIA. Different statistical methods used to identify hormone secretion profiles revealed a characteristic pulsatile pattern of LH and FSH in plasma. However, LH pulses were more frequent and had greater amplitude than FSH pulses. Less than 32% of the FSH pulses were associated with LH episodes. Conversely, the association between LH and testosterone pulses averaged 83% in birds with testis weight greater than 10 g. Concentrations of corticosterone tended to increase after cannulation and remained elevated for only 3-4 h. Our data indicate that LH, FSH, and testosterone secretion is pulsatile in male broiler breeders. Additionally, LH pulses are associated with testosterone episodes but not with FSH pulses. The pulsatile pattern of FSH secretion, which is unique from those of LH, in adult males suggests that FSH secretion is independently regulated in the adult male fowl.

Dietary protein restriction stress in the domestic chicken (Gallus gallus domesticus) induces remodeling of adrenal steroidogenic tissue that supports hyperfunction

The stress of dietary protein restriction in the immature domestic turkey (Meleagris gallopavo) induces adrenal steroidogenic hypofunction that is associated with an alteration in the proportion of density-dependent subpopulations of steroidogenic cells within the adrenal gland. In contrast, when imposed on immature chickens, this nutritional stressor induces long-term enhancement of adrenal steroidogenic function. However, whether this alteration in function is accompanied by a remodeling of chicken adrenal steroidogenic tissue as in the turkey is not known. To address this question, immature cockerels (2 weeks old) were fed established isocaloric synthetic diets containing either 20% (control) or 8% (restriction) soy protein for 4 weeks. Adrenal glands were processed for the isolation of defined, density-separable, adrenal steroidogenic cell subpopulations: three low-density adrenal steroidogenic cell subpopulations [LDAC-1 (rho = 1.0285-1.0430 g/ml), LDAC-2 (rho = 1. 0430-1.0485 g/ml), and LDAC-3 (rho = 1.0485-1.0500 g/ml)] and one high-density subpopulation [HDAC (rho = 1.0510-1.0840 g/ml)]. The steroidogenic function of these cell subpopulations was assessed. Protein restriction consistently, but differentially, enhanced maximal ACTH-induced corticosterone production by the subpopulations: values of LDAC-1, -2, and -3 and HDAC from protein restricted birds were, respectively, 116, 43, 33, and 20% greater than those of corresponding cell subpopulations from control birds. However, it had contrasting influences on maximal ACTH-induced aldosterone production by the cell subpopulations. Whereas the value of LDAC-1 from protein-restricted birds was 70% greater than that from control birds, the values for LDAC-2 and -3 were not different from those of the control, and the value for HDAC was 22% less than that of the control. Protein restriction also altered the cell subpopulation composition of the adrenal gland: compared to control, it increased the proportion of LDAC-1 by 46% and decreased the proportion of LDAC-3 and HDAC by 34 and 20%, respectively. Thus, dietary protein restriction increased the proportion of cells (i.e., LDAC-1) having the greatest enhancement in corticosteroid production. This pattern of remodeling of chicken adrenal steroidogenic tissue in response to dietary protein restriction contrasts sharply with the pattern that occurs in another galliform species, the domestic turkey.

Dietary protein restriction stress in the domestic turkey (Meleagris gallopavo) induces hypofunction and remodeling of adrenal steroidogenic tissue

In the present study, we investigated the influence of dietary protein restriction stress on adrenal steroidogenic function of the domestic turkey. Immature male turkeys (2 weeks old) were fed isocaloric synthetic diets containing either 28% (control) or 8% (restriction) soy protein for 4 weeks. Trunk plasma was processed for the determination of adrenocorticotropin (ACTH), corticosterone, aldosterone, and total 3, 5, 3'-triiodothyronine (T3). In addition, adrenal glands were processed for the isolation of defined, density-separable, adrenal steroidogenic cell subpopulations: three low-density adrenal steroidogenic cell subpopulations [LDAC-1 (rho = 1.0350-1.0490 g/ml). LDAC-2 (rho = 1.0490-1.0570 g/ml), and LDAC 3 (rho = 1.0370-1.0585 g/ml)] and a high-density subpopulation [HDAC (rho = 1.0590-1.0720 g/ml)], and the steroidogenic function of these cell subpopulations was evaluated. Protein restriction did not influence plasma ACTH However, it increased relative adrenal weight (mg/100 g body wt) (+37.8%) and plasma corticosterone (+317%). By contrast, it depressed plasma aldosterone (-51.2%). In addition, it caused a modest depression in plasma T3 (-25.9%). At the cellular level, protein restriction induced panhypofunction. Basal corticosteroid (aldosterone and corticosterone) production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds were, respectively, 42.9, 47.9, 30.8, and 57.5% less than those of corresponding cell subpopulations from control birds. In addition, maximal corticosteroid production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds, in response to ACTH, angiotensin II (AngII), and 25-hydroxycholesterol support, were depressed by 56.8, 55.1, 22.7, and 42.9%, respectively. Interestingly, LDAC-3 was relatively refractory to the influence of this stressor. By contrast, there was the lack of a concentration-dependent aldosterone response of LDAC-1 and -2 to AngII with protein restriction. This was not due to a failure in cell function since aldosterone responses of these cell subpopulations to ACTH and to 25-hydroxycholesterol support were apparent. In addition, the concentration of AngII receptors of cell subpopulations from protein-restricted turkeys, if anything, was greater than that of cell subpopulations from control turkeys. Protein restriction also altered the cell subpopulation composition of the adrenal gland: compared to control, it decreased the proportion of LDAC-2 by 42.3% and increased the proportion of LDAC-3 and HDAC by 68.7 and 302%, respectively. Thus, dietary protein restriction induces adrenal steroidogenic hypofunction in turkeys. In addition, the present study suggests that this nutritional stressor induces marked remodeling of the steroidogenic tissue in the turkey adrenal gland.

Selection of foods by broiler chickens following corticosterone administration

1. The effects of corticosterone (CORT) on diet selection of broiler chickens offered a choice of a high protein concentrate (381 g CP/kg, 17.5 MJ/kg ME) and whole wheat (113 g CP/kg, 15.9 MJ/kg ME) in relation to age were examined in two experiments. 2. Daily intramuscular injections of 2 and 4 mg/kg of CORT for a 5-d period in both 2- and 5-week-old chickens resulted in increases in total food, protein and energy intakes. This led to a decrease in protein accretion in older but not younger chicks, an increase in total lipid contents of the carcase at both ages, and produced changes in internal organs. 3. CORT significantly reduced body weight gain of young but not old chickens, suggesting that mature birds respond better than young ones to the physiological changes caused by treatment, by making subsequent appropriate food choices. 4. Administration of CORT in young chicks increased wheat intake at 2 and 4 h after injection, while in older birds a similar increase was maintained up to 24 h after injection. Intake of HP food was decreased by both doses of CORT in young chicks but there was no significant effect in older chickens. 5. Changes in energy: protein ratio in the chosen diet appeared at 4 h after treatment in old chickens and at 24 h in younger chicks. 6. The results suggest that birds are able to detect metabolic changes caused by CORT administration and attempt to redress them by modifying their food pattern. The time course of the response of birds to these changes is age related. However, the food selection pattern did not completely compensate for the physiological defects.

The effects of halofuginone and salinomycin, alone and in combination, on live performance and skin characteristics of female broilers: influence of a high-proline diet supplemented with ascorbic acid and zinc

Live performance and carcass quality of female broilers were evaluated under four coccidiostat programs (CP) and two feed treatments. The CP consisted of halofuginone (H) and salinomycin (S), fed either continuously (HH and SS) or in rotational programs (HS and SH), during the starter (1 to 21 d) and grower (22 to 35 d) periods, respectively. All groups received an unmedicated withdrawal feed from 36 to 42 d. Feed treatments consisted of a control and a fortified diet high in proline and supplemented with additional ascorbic acid and zinc (50 birds per pen; 4 pens per feed; 8 pens per CP). In addition to live performance and skin puncture strength, carcass quality attributes following processing (at 43 d of age) were assessed. No CP by feed interactions were detected for any of the variables measured. The CP treatments did not differ for live performance. Birds on fortified feed were heavier at 21 d (P < .001) and had an improved feed conversion at 42 d (P < .05). Skin puncture strength was significantly reduced for the birds fed H, either in continuous (HH) or rotational programs (HS and SH). Skin sores-scratches and tears were lowest for the SS and SH groups. The HH treatment resulted in fewer grade A carcasses (P < .001). Halofuginone, when fed continuously or in the starter feed, affected carcass quality of broilers. Higher dietary proline or supplementation with ascorbic acid and zinc did not appear to alleviate the effects of halofuginone on skin quality.

Self-selection of ascorbic acid in coloured foods by heat-stressed broiler chicks

Female broiler chicks were given red and green supplemented (200 mg ascorbic acid (AA)/kg) and unsupplemented foods on alternate days for 8 days under heat-stressed and unstressed conditions. After this training period, the birds were given access to both foods, and the intake of each was monitored. In both heated treatments the intake of the supplemented food was significantly higher (p < 0.05) than of the unsupplemented food (800 vs. 518 g/14 days), although in the unheated groups significantly more of the unsupplemented food was eaten (756 vs. 639 g/14 days). Birds were unable to select for AA when neither food was coloured, even when they were presented continuously in the same positions in the cage. It is concluded that chicks can learn to associate the colour of the food with its AA content and that they select proportions of supplemented and unsupplemented foods appropriate for their needs, as influenced by environmental temperature.

Response of White Leghorn chicks fed ascorbic acid and challenged with Escherichia coli or with corticosterone

This study was undertaken to assess the effects of dietary ascorbic acid on the growth and immunoresponsiveness of chickens when subjected to particular types of stress. White Leghorn chicks were fed diets containing no supplemental ascorbic acid, and ascorbic-acid diet (330 ppm) for 2 days or for 19 days before challenge. Then, half of the females were inoculated with Escherichia coli; half of the males were challenged with dietary corticosterone (30 ppm) for 12 days; and the remaining chicks were maintained as controls. These chicks, reared under "good" husbandry procedures, did not realize advantages in growth or feed efficiency due to the short- or long-term consumption of diets containing ascorbic acid. Incubation with E. coli resulted in considerably higher heterophil-to-lymphocyte ratios 24 h after inoculation, and E. coli-induced mortality was higher for pullets on short-term ascorbic acid than for those on long-term or no ascorbic acid. Dietary corticosterone caused differences in body weight and the relative weights of certain organs, regardless of dietary levels of ascorbic acid. The antibody response to red-blood-cell antigens from sheep was enhanced in unchallenged cockerels (no dietary corticosterone) fed ascorbic acid on a long-term basis, but dietary corticosterone overshadowed the advantageous effects of dietary ascorbic acid. These data showed that the effects of supplemental ascorbic acid on growth and on immunoresponsiveness were related to the quality of the husbandry, length of supplemental feeding, age of the chicks, endogenous-exogenous balance for ascorbic acid, and the relationship with corticosterone.

Daily changes in plasma prolactin, corticosterone, and luteinizing hormone in the unrestrained, ovariectomized turkey hen

Plasma concentrations of prolactin (PRL), corticosterone (B), and luteinizing hormone (LH) were determined in hourly samples collected over a 24-h period from unrestrained, long-term ovariectomized (OVX) turkey hens maintained in cages in an isolation room on a 14 h light: 10 h dark photoperiod. Mean plasma concentrations of all three hormones were found to vary significantly with the time of sampling. Mean plasma PRL levels reached a peak (6.50 +/- 1.70 ng/mL, means +/- SEM) during the latter half of the photophase, declined to a nadir (5.22 +/- 1.20 ng/mL) prior to the onset of darkness, and then rose gradually during the scotophase to reach another peak (8.96 +/- 1.80 ng/mL) 1 h prior to lights on. Mean plasma LH levels rose significantly (P less than .001) from a nadir of 4.11 + .29 ng/mL prior to lights out to a peak of 4.74 + .34 ng/mL during the dark period. No evidence of random fluctuations in LH levels was observed in any individual, suggesting that episodic LH release may not occur in OVX turkey hens. Individual patterns of B secretion varied substantially so that, although significant increases and decreases in mean plasma B levels were observed, no clearly defined peaks in mean plasma B levels were identified. Individual secretory profiles revealed that peaks in PRL secretion often coincided with peaks in B secretion, but B peaks were usually more numerous. It is concluded that PRL and LH are secreted in a daily rhythm in the OVX turkey hen, with the highest levels of both hormones occurring during the scotophase.

The role of vitamins in modulating disease resistance

Many of the metabolic incursions resulting from stress and oxidative damage are detrimental to disease resistance. Vitamins A, E, and C and carotenoids are able to protect cells from free radical oxidation, reduce the detrimental effects of certain eicosanoids, and enhance humoral and cellular immune responses in disease. The regulation of cell differentiation by vitamin A in maintaining an epithelial barrier to pathogen entry and the differentiation of precursor cells to functional lymphocytes by 1,25-dihydroxycholecalciferol are essential to disease resistance. Nutritionists must redefine the levels of vitamins necessary to maximize health-supportive systems. The animal's metabolism must constantly be adjusting to its environmental stress or disease and may require increased vitamins.

Effect of adrenocorticotropin and dietary ascorbic acid on cutaneous basophil hypersensitivity to phytohemagglutinin in chickens

Two trials were conducted to assess the effects of adrenocorticotropin (ACTH) and dietary ascorbic acid (AA) on cutaneous basophil hypersensitivity (CBH) to phytohemagglutinin (PHA-P) in chickens. Broiler chicks received AA at levels of 0, 150, or 300 mg/kg of feed (ppm) continuous from hatching. At 6 to 7 wk of age, birds from each AA group received either 2 IU ACTH/100 g of body weight, 4% gelatin, or no ACTH or gelatin injections. Injections were given 12 h prior to, at the time of, and at 12 and 24 h after an intradermal wattle injection with PHA-P. Responses to PHA-P were determined as wattle indices. Injections of ACTH reduced body weight gain in both trials and decreased relative bursa weight in Trial 1. Injections of ACTH and dietary AA increased plasma cholesterol in both trials. Peak CBH wattle response occurred at 24 h post PHA-P injection. Injections of ACTH decreased mean wattle index at 18 and 36 h post PHA-P injection in Trial 1 and 18 and 24 h post PHA-P injection in Trial 2. The addition of AA ameliorated the ACTH-mediated suppression of CBH in a dose-related manner.

Polyhormonal regulation of avian and mammalian corticosteroidogenesis in vitro

1. The combined actions of ACTH, corticosterone and prolactin (PRL) in the acute regulation of corticosteroidogenesis were investigated using isolated adrenocortical cells from intact and hypophysectomized (hypox) rats (Rattus norvegicus) and from intact male domestic fowl (Gallus gallus domesticus). 2. Exogenous corticosterone suppressed to about 50% ACTH-induced corticosterone production of cells from either species. This suppression, in part, was due to corticosterone degradation. 3. oPRL, in the presence or absence of ACTH, raised corticosterone production of hypox rat cells, but not intact rat and domestic fowl cells. 4. In addition, oPRL counteracted the corticosterone-induced suppression of net ACTH-stimulated corticosterone production of hypox rat and intact domestic fowl cells, but not intact rat cells. 5. The potency of oPRL with domestic fowl cells was 4 times that with hypox rat cells. 6. Furthermore, in domestic fowl cells, the effect of oPRL was Ca2+-dependent.

Comparison of the adrenal sensitivity to ACTH of laying hens with immobilization and plasma baseline levels of corticosterone

The effects of mammalian ACTH (0.01-10.0 IU/kg) given intraarterially on plasma corticosterone levels in laying hens were determined. A rectilinear dose-response relationship was found, y = 24.545 + 8.691x. Daily ACTH injections of 0.1 IU/kg on 3 successive days showed a good reproducibility in response in plasma corticosterone levels. Immobilization by hand also increases plasma corticosterone to a plateau level of about 4 ng/ml. The effects of ACTH and immobilization in individual birds showed a good correlation (r = 0.87). A rather low correlation (r = 0.49) existed between individual baseline levels of plasma corticosterone and adrenal sensitivity for ACTH. The adrenal sensitivity for ACTH was nearly two times higher in the morning than in the evening. A diurnal pattern, however, could not be shown in the corticosterone response to immobilization.

In vivo responsiveness of the broilers' adrenocortical system

The possible interaction of circadian rhythms in serum concentrations of corticosterone (B) with the response of broiler cockerels to heat stress (HS) and adrenal manipulation with adrenocorticotropic hormone (ACTH) and dexamethasone acetate (DA) was investigated. Adrenocortical response, as indicated by corticosterone concentrations, was greater early in the photoperiod in cockerels exposed to HS or injected with ACTH. A single injection of DA tended to be more inhibitory on B when administered later in the photoperiod.

Influence of supplemental ascorbic acid on broiler performance following exposure to high environmental temperature

The present study was conducted to determine if dietary ascorbic acid (AA) would improve growth, feed efficiency, and livability of broilers following an acute heating episode. Supplemental AA was provided in the diets at calculated levels of 0, 250, 500, and 1000 ppm, continuously. Females that received 1000 ppm exhibited significantly greater body weights at 2 and 4 weeks of age. No significant effects due to AA supplementation were observed in body weights of males. At 4 weeks of age, chicks were heated on two consecutive days by increasing the ambient temperature (38.3 C at bird level) in the production facility. Heating significantly reduced body weights in males, but not females, at 5 and 7 weeks of age. Feed conversions were increased after heating, but significant effects due to AA were not found. Ascorbic acid did not improve overall livability significantly in either sex, but heat-associated mortality was reduced in supplemented females.

Serum lipoproteins in chickens after administration of adrenocorticotropin or exposure to high temperature

The effects of intramuscular injections of adrenocorticotropin (ACTH) or short-term exposures to high environmental temperature (44 to 46 C) were determined on the relative amounts of lipoproteins in the serum of 6 to 7-week-old White Rock chickens. In addition, the influence of the sex of the bird and fasting vs. ad libitum feeding on these lipoproteins was measured. The relative amount of high density lipoprotein (HDL) was lowered by ACTH, and heat exposure lowered both HDL and very low density lipoprotein (VLDL). Fasting completely eliminated VLDL and lowered low density lipoprotein (LDL) but had little effect on HDL. The temperature treatments significantly increased serum corticosteroid levels in both sexes in birds fed ad libitum but only in the males of fasted birds. Fasting for 15 hr did not significantly affect serum corticosteroid levels.

Factors affecting broiler processing parameters and plasma corticosterone

Two experiments were conducted to determine the influence of broiler strain, sex, and age on resting plasma corticosterone levels and the latter's relationship to various broiler production and processing parameters. In Experiment 1, strain and sex differences in 58-day farm weight (FWT), dressed carcass weight (DC), yield (Y), abdominal fat (AF), abdominal fat expressed as a percentage of DC (PAF), and plasma corticosterone (C) measures were assessed in five commercial broiler strains fed a lower [3086 kcal metabolizable energy (ME)/kg] versus higher (3306 kcal ME/kg) energy ration. The higher energy diet was formulated and used to produce excess abdominal fat. In Experiment 2, the effect of broiler age (4, 6, and 8 weeks) on resting plasma C was determined. Results of Experiment 1 indicated that although strain significantly influenced AF, and although feeding the higher energy diet significantly elevated FWT, DC, Y, AF, and PAF, strain and dietary energy effects on plasma C were nil. However, a significant strain X dietary energy interaction on plasma C levels was observed. Likewise, although female broilers had greater PAF measures than male birds, sex did not influence resting plasma C values. Plasma C was not correlated to AF measures. Experiment 2 results showed plasma C at 6 (3.3 ng/ml) and 8 weeks (2.9 ng/ml) was significantly depressed from the 4-week (4.9 ng/ml) sampling. Thus, future studies involving adrenal functioning in broilers should take into consideration the influence bird age might have on interpretation of results.

Dietary ascorbic acid or procaine penicillin and the response of the immature fowl to stressors

1. The effectiveness of dietary ascorbic acid and procaine penicillin in ameliorating the response to the stressors glucagon, corticotrophin, withdrawal of food and water and extremes of environmental temperature, both short and long-term, has been assessed. 2. No consistent changes in the responses were found, but it is suggested that the rates of inclusion of the substances may be important.