Selection of foods by broiler chickens following corticosterone administration

Prenatal yolk corticosterone exposure promotes skeletal growth and induces oxidative imbalance in yellow-legged gull embryos

Maternally derived hormones induce variation in offspring phenotype, with consequences that can carry over into post-natal life and even into adulthood. In birds, maternal egg corticosterone (CORT) is known to exert contrasting effects on offspring morphology, physiology and behaviour after hatching. However, information on the effects of CORT exposure on pre-hatching embryonic development is limited. We experimentally increased yolk CORT levels in yellow-legged gull (Larus michahellis) eggs, and assessed the effects on embryo pre-hatching development and oxidative status of brain and liver. CORT-supplemented embryos reached a larger skeletal size and liver mass compared with controls. Embryos from CORT-injected last-laid eggs showed decreased activity of the hepatic antioxidant enzymes superoxide dismutase and catalase, while intermediate-laid eggs showed increased levels of lipid peroxidation. However, elevated yolk CORT did not affect oxidative stress endpoints in the brain. Our results indicate that elevated yolk CORT levels affect prenatal embryo development by promoting skeletal growth, and induce laying sequence- and organ-specific oxidative imbalance, with potential adverse consequences during postnatal life, especially for late-hatched offspring.

Heat Stress Responses in Birds: A Review of the Neural Components

Heat stress is one of the major environmental conditions causing significant losses in the poultry industry and having negative impacts on the world's food economy. Heat exposure causes several physiological impairments in birds, including oxidative stress, weight loss, immunosuppression, and dysregulated metabolism. Collectively, these lead not only to decreased production in the meat industry, but also decreases in the number of eggs laid by 20%, and overall loss due to mortality during housing and transit. Mitigation techniques have been discussed in depth, and include changes in air flow and dietary composition, improved building insulation, use of air cooling in livestock buildings (fogging systems, evaporation panels), and genetic alterations. Most commonly observed during heat exposure are reduced food intake and an increase in the stress response. However, very little has been explored regarding heat exposure, food intake and stress, and how the neural circuitry responsible for sensing temperatures mediate these responses. That thermoregulation, food intake, and the stress response are primarily mediated by the hypothalamus make it reasonable to assume that it is the central hub at which these systems interact and coordinately regulate downstream changes in metabolism. Thus, this review discusses the neural circuitry in birds associated with thermoregulation, food intake, and stress response at the level of the hypothalamus, with a focus on how these systems might interact in the presence of heat exposure.

Effects of Dietary Energy Level on Performance, Plasma Parameters, and Central AMPK Levels in Stressed Broilers

This study aimed to characterize the effects of diets with different energy levels on the growth performance, plasma parameters, and central AMPK signaling pathway in broilers under dexamethasone (DEX)-induced stress. A total of 216 1-day-old male broiler chickens were allocated to groups fed with high (HED), National Research Council-recommended (control), or low (LED) energy diets. At 10 days old, chickens were treated with or without dexamethasone (DEX, 2 mg/kg body weight) for 3 consecutive days. HED increased broiler average daily gain (ADG) at 10 days old, compared with the LED (P < 0.05), while average daily feed intake (ADFI) and feed conversion rate (FCR) decreased as the dietary energy level increased (P < 0.05). Chickens fed a HED had higher total protein (TP) content, albumin (ALB), glucose (GLU), total cholesterol (TCHO), high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol, compared with the control group (P < 0.05). At 13 days old, DEX decreased ADG and increased FCR in broilers fed with different energy diets (P < 0.05). The DEX-HED group had a higher ADFI than non-DEX treated HED group chickens. In addition, TP, ALB, triglycerides (TG), TCHO, HDL, and LDL content levels in the DEX group were higher than those in the control group (P < 0.05). The uric acid (UA) content of the LED group was higher than that of the HED group (P < 0.05). Further, gene expression levels of liver kinase B1, AMP-activated protein kinase α1, neuropeptide Y, and GC receptor in the hypothalamus were increased in chickens treated with DEX (P < 0.05). There was a trend toward interaction between plasma TCHO and hypothalamic LKB1 expression (0.05 < P < 0.1). In conclusion, this study suggests that HED improves growth performance, plasma glucose and total cholesterol at 10 days old broilers, but had no significant effect on performance, plasma parameters, and central AMPK in stressed broilers.

Effects of dietary corticosterone on the central adenosine monophosphate-activated protein kinase (AMPK) signaling pathway in broiler chickens

Glucocorticoids (GCs) induce the activation of the central adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling pathway in birds. In this study, we aimed to investigate the effects of corticosterone (CORT) supplemented in diet on the central AMPK signaling pathway in broilers. The average daily gain was reduced by CORT treatment, and the average daily feed intake remained unchanged. Plasma glucose, triglyceride, total cholesterol, and CORT contents were increased by CORT administration. In addition, CORT treatment decreased the relative weights of heart, spleen, and bursa and increased the relative weights of liver and abdominal fat. The glycogen contents in the liver and breast muscle were higher in the chicks treated with CORT. CORT treatment upregulated the gene expression of mammalian target of rapamycin, glucocorticoid receptor, AMPKα2, neuropeptide Y(NPY), liver kinase B1 (LKB1), AMPKα1, and fatty acid synthase in the hypothalamus. Moreover, CORT treatment increased the protein levels of acetyl-coenzyme A carboxylase (ACC) phosphorylation and total AMPK and phosphorylated AMPK in the hypothalamus. Hence, CORT administration in the diet activated the LKB1-AMPK-NPY/ACC signaling pathway in the hypothalamus of broiler.

The role of 5-HT2c receptor on corticosterone-mediated food intake

Corticosterone plays an important role in feeding behavior. However, its mechanism remains unclear. Therefore, the present study aimed to investigate the effect of corticosterone on feeding behavior. In this study, cumulative food intake was increased by acute corticosterone administration in a dose-dependent manner. Administration of the 5-HT_2c receptor agonist m-chlorophenylpiperazin (mCPP) reversed the effect of corticosterone on food intake. The anorectic effects of mCPP were also blocked by the 5-HT_2c receptor antagonist RS102221 in corticosterone-treated mice. Both corticosterone and mCPP increased c-Fos expression in hypothalamic nuclei, but not the nucleus of the solitary tract. RS102221 inhibited c-Fos expression induced by mCPP, but not corticosterone. In addition, mCPP had little effect on TH and POMC levels in the hypothalamus. Furthermore, mCPP antagonized decreasing effect of the leptin produced by corticosterone. Taken together, our findings suggest that 5-HT_2c receptors and leptin may be involved in the effects of corticosterone-induced hyperphagia.

Effect of dexamethasone on hypothalamic expression of appetite-related genes in chickens under different diet and feeding conditions

BACKGROUND

Glucocorticoids (GCs) are involved in the control of appetite in birds and mammals. The effect of GCs on feed intake in birds depends on their dietary energy level. But the regulation mechanism of GCs on appetite is still unclear in chickens facing to different energy level. An experiment was conducted to investigate the effect of dexamethasone (DEX) on hypothalamic expression of appetite-related peptides in chickens fed high/low fat diet and under fasting/feeding condition.

RESULTS

An interaction between DEX injection and dietary energy level was found on hypothalamic corticotropin-releasing hormone (CRH) gene expression in fasted chickens (P < 0.05). The chickens, given a DEX injection and a low fat diet treatment, had the highest CRH mRNA levels than any of the fasted chickens given treatments (P < 0.05). Under fasting conditions, the DEX treatment significantly increased hypothalamic neuropeptide Y (NPY) and GC receptors mRNA levels (P < 0.05). Under re-feeding conditions, DEX treatment significantly decreased hypothalamic expression levels of NPY and agouti-related peptide (AgRP) but significantly increased the level of hypothalamic CRH expression (P < 0.05).

CONCLUSION

A regulatory network formed by NPY, AgRP and CRH is associated with the appetite-control by GCs. The result suggests that the regulation of GCs on orexigenic neuropeptides expression is dependent at least partially on dietary energy level and feeding state.

Micro-encapsulated sodium butyrate attenuates oxidative stress induced by corticosterone exposure and modulates apoptosis in intestinal mucosa of broiler chickens

The aim of the present study was to investigate the effects of micro-encapsulated sodium butyrate (MSB) on oxidative stress and apoptosis induced by dietary corticosterone (CORT) in the intestinal mucosa of broiler chickens. In total, 120 1-day-old male broilers (Arbor Acres) were randomly allocated to two treatment groups and were fed on a control diet (without MSB) or 0.4 g MSB/kg diet. Each treatment had six replicates with five chickens each. From 7 days of age onward, 50% of the chickens in each dietary treatment were subjected to CORT treatment (30 mg/kg of diet). The experimental period was 21 days. The results showed that CORT administration decreased (P < 0.001) feed intake and bodyweight gain and increased (P < 0.001) feed to gain ratio (F : G) of broiler chickens. The dietary MSB supplementation decreased (P < 0.01) F : G and there was an interaction between MSB and CORT on F : G (P < 0.05). Moreover, the activities of superoxide dismutase, glutathione peroxidase and catalase in intestinal mucosa were decreased (P < 0.01 or P < 0.001), and the concentrations of malondialdehyde in the intestinal mucosa were elevated (P < 0.01) by CORT administration. In contrast, treatment of MSB increased (P < 0.01) the catalase activities in duodenal and jejunal mucosa and decreased (P < 0.01) the malondialdehyde concentrations in duodenal mucosa. Higher apoptosis index and lower mRNA expressions of bcl-2 in intestinal epithelial cells were induced (P < 0.05) by CORT treatment. However, MSB decreased (P < 0.05) the apoptosis index and increased the bcl-2 expression. These results suggest that dietary MSB can partially attenuate oxidative stress induced by CORT treatment and inhibit apoptosis of intestinal epithelial cells in broiler chickens.

Chicks change their pecking behaviour towards stationary and mobile food sources over the first 12 weeks of life: improvement and discontinuities

Chicks (Gallus gallus domesticus) learn to peck soon after hatching and then peck in rapid bursts or bouts with intervals of non-pecking activity. The food sources may be static such as seeds and chick crumb, or mobile such as a mealworm. Here, changes with age in pecking toward chick crumb and a mealworm were measured.

Chicks were reared in pairs and their pecking of crumb food was video recorded in their pair housed environment, from food presentation, every third day from day 8 (wk 2) to day 65 (wk 10). Peck rate at crumb food reached maximum levels at day 32 (wk 5), and then declined, fitting a quadratic model, with no sex, sex of cagemate, or box order effects. Within bouts the peck rate was higher and it increased to day 41 (wk 6) and then declined, and here males pecked faster than females. A change in dietary protein concentration from 22% to 18% at day 28 (wk 4) had no effect on subsequent peck rate.

Pecking at and consumption of a mealworm in pair housed chicks were measured weekly from wks [5 to 12]. The latency to first worm peck and latency to swallow decreased to wk 8 and increased thereafter. The peck rate to first wormpeck and number of pecks to swallow increased to wk 8 and then declined paralleling the changes with crumb food. The increase in peck rate is coupled with an increase in efficiency in worm catching.

The results are consistent with the view that the improvement in pecking ability and accuracy compliments change in nutritional requirement best served by an invertebrate food (IF) source requiring speed to achieve feeding success, especially with live prey. When this food source is no longer crucial these associated skill levels decline. An appreciation of the role of domestic fowl in controlling insect populations, at farm level, that are often vectors in disease spread is lacking.

Effect of corticosterone on gene expression of feed intake regulatory peptides in laying hens

The present study was conducted to explore the effects of corticosterone (CORT) on the regulation of appetite-associated genes in laying hens. Forty eight laying hens were randomly divided into two groups: one received subcutaneous injection of CORT (2mg/kg body weight, CORT-exposed) and the other received sham-treatment (Control). Treatment of hens with CORT stimulated an increase (P<0.05) in plasma CORT, glucose, uric acid (UA), insulin, cholesterol (Chol) and triiodothyronine (T(3)), but the concentrations of plasma non-esterified fatty acids (NEFA) and triacylglycerol (TG) were decreased (P<0.05). CORT treatment had no significant effect (P>0.05) on the mRNA levels of neuropeptide Y (NPY), corticotropin-releasing hormone (CRH), melanocortin receptor 4 and 5 (MCR-4 and MCR-5) and cholecystokinin (CCK) in the hypothalamus when compared with control hens. However, the expression of pro-opiomelanocortin (POMC), agouti-related protein (AgRP) and melanocortin recepter 1 (MCR-1) were significantly (P<0.05) suppressed while the mRNA levels of ghrelin and cocaine-and amphetamine-regulated transcript (CART) were significantly upregulated (P<0.05) in CORT-treated hens. Treatment of laying hens with CORT had no significant (P>0.05) effect on the mRNA levels of CCK in the glandular stomach and the duodenum, and those of ghrelin in the glandular stomach, the duodenum and the jejunum. However, the mRNA levels of CCK in the jejunum and the ileum, and those of ghrelin in the ileum were significantly (P<0.05) suppressed by CORT treatment. In conclusion, these results suggest that CORT plays a unique role in some special neuropeptides (e.g., ghrelin, CART, POMC, CCK and MCRs) and a dynamic balance between these appetite-associated peptides in the hypothalamus and the gastrointestinal tract defines the feeding status of CORT-exposed laying hens.

Perspectives on the endocrinology of poultry growth and metabolism

Birds have rapid pre- and post-hatching growth rates. The major hormones required to support normal growth are growth hormone (GH), triiodothyronine (T(3)) and insulin-like growth factor-I (IGF-I). Optimal growth requires a "set-point" concentration of both IGF-I and T(3) in the circulation. Pituitary GH plays a role in controlling the circulating concentrations of both IGF-I and T(3). Nutritional restriction (energy, protein) leads to reductions in circulating concentrations of both IGF-I and T(3) with increased GH secretion due removal of negative feedback. Similarly, there is un-coupling of the GH-IGF-I axis in stunting disease. A critical control point is at the level of the liver and GH receptor/signal transduction. The major hormones controlling metabolism include glucagon, insulin, adrenal glucocorticoid hormone, corticosterone and potentially somatostatin. Chickens and turkeys have higher circulating concentrations of glucose than those of livestock mammals. What are not known include the following: the biological basis for the high basal glucose concentrations; the quantitative fluxes of key metabolites in the fed and fasted state through growth and development; the relative contribution of different organs to gluconeogenesis; the relative importance of insulin and somatostatin in controlling lipolysis and the role of gastro-intestinal hormones in the control of metabolism.

Corticosterone administration and dietary glucose supplementation enhance fat accumulation in broiler chickens

1. The effects of exogenous corticosterone administration and glucose supplementation on energy intake, lipid metabolism and fat deposition of broiler chickens were investigated. 2. A total of 144 three-d-old male chickens were randomly assigned to one of the following 4 treatments for 7 d: a low energy diet (10.9 MJ ME/kg, 200 g/kg CP) with or without corticosterone (30 mg/kg diet) and drinking water supplemented with glucose (80 g/l) or saccharine (2 g/l, control). 3. Body weight (BW) gain and breast and thigh muscle yields (% body mass) were all significantly decreased by corticosterone treatment. The relative cumulative feed intake (RCFI) and relative ME intake (RMEI), rather than the feed (FI) or ME intake (MEI) were increased by corticosterone administration. Both feed efficiency (FE) and caloric efficiency (CE) were decreased by corticosterone administration. Corticosterone administration had no obvious effect on water consumption. 4. Glucose supplementation had no influence on BW gain and breast and thigh muscle yield (as % of body mass). FI or RCFI was decreased while MEI or RMEI was increased by glucose supplementation. FE was improved by glucose treatment, whereas CE was reduced. 5. Liver weight and abdominal, cervical and thigh fat deposits were all significantly increased by either corticosterone or glucose treatment. 6. Plasma concentrations of glucose, urate, triglyceride, non-esterified fatty acids (NEFA), very low density lipoprotein and insulin were all significantly increased by corticosterone treatment. Glucose supplementation had no obvious influence on any of the measured plasma parameters except for NEFA, which were significantly increased. 7. Lipoprotein lipase activities in either cervical or abdominal adipose tissues, rather than in thigh fat tissue, were significantly elevated by either glucose or corticosterone treatment.

Corticosterone administration and high-energy feed results in enhanced fat accumulation and insulin resistance in broiler chickens

1. Two experiments were conducted to investigate the effects of exogenous corticosterone administration (30 mg/kg diet) and dietary energy level on feed or energy intake and fat deposition in broiler chickens of 1 and 4 weeks of age. 2. Corticosterone treatment significantly suppressed body weight (BW) gain and reduced feed and caloric efficiencies. The retarded growth may conceal the stimulatory effect of corticosterone on feed consumption or metabolisable energy (ME) intake. A high-energy diet may increase energy intake and partially alleviate the suppressing effect of corticosterone on growth of broilers. 3. Corticosterone administration promoted the conservation of energy stores as fat at both abdominal and subcutaneous sites and this process occurred regardless of dietary energy level in ad libitum feeding status. A high-energy diet increased fat accumulation and showed no significant interaction with corticosterone treatment. 4. The suppressed development of breast and thigh muscles by corticosterone treatment was observed only in 1-week-old chickens fed on the low-energy diet. In contrast, the yield of breast muscle but not thigh muscle was significantly decreased by corticosterone in 4-week-old chickens, suggesting that the tissue specificity to corticosterone challenge is age dependent. 5. Plasma concentrations of glucose, insulin, triglyceride, non-esterified fatty acids (NEFA) and very low density lipoprotein were increased by corticosterone treatment regardless of diet treatment. A high-energy diet increased plasma levels of NEFA and resulted in hyperinsulinism in 4-week-old chickens but not in 1-week-old chickens. 6. Lipoprotein lipase (LPL) activities in adipose tissues may have been up-regulated by corticosterone treatment and showed tissue specificity. The increased LPL activities at ad libitum feeding status were not necessarily linked with the increased fat accumulation in corticosterone challenged chickens. 7. Corticosterone resulted in augmented energy consumption and altered energy redistribution toward lipid deposition. The induced insulin resistance and enhanced hepatic de novo lipogenesis by corticosterone are likely to be responsible for the increased fat deposition.

Effects of corticosterone treatment on growth, development, and the corticosterone response to handling in young Japanese quail (Coturnix coturnix japonica)

Corticosterone, a glucocorticoid secreted during stress responses, has a range of actions that help birds respond to stressors. Although effects of corticosterone treatment have been described in several avian species, the impacts of defined increases in plasma corticosterone on early development and on corticosterone stress responses are little known. These issues were addressed by providing quail with different doses of corticosterone in drinking water from days 8 to 38 post-hatch. The corticosterone dose consumed by each bird during treatment days 15-30 was calculated by measuring water intake. The corticosterone dose was inversely, but weakly, correlated with weights of the bursa, thymus, spleen, liver, testes, oviduct, muscle, and body, and positively correlated with peritoneal fat deposition. When birds were divided into groups based on their corticosterone intake, weights of the spleen, thymus, bursa, muscle, testes, and oviduct were significantly reduced in birds receiving the highest doses; with the exception of muscle, similar reductions were also observed in birds receiving medium doses, and thymic growth was inhibited in birds receiving low doses. The acute corticosterone stress response was measured by handling birds for 15 min. Plasma corticosterone was transiently increased at 15 min in control birds in response to the handling stressor. Some birds consuming low doses of corticosterone had corticosterone responses similar to control birds. Initial corticosterone concentrations were elevated in birds consuming higher doses of corticosterone. Plasma corticosterone in these birds decreased from 0 to 15 min, then increased from 15 to 30 min. The initial decrease could be due to corticosterone clearance, whilst the increase could indicate that the birds had a greater response than control birds to isolation as a stressor. Corticosterone treatment may have reduced the strength of corticosterone negative feedback within the hypothalamo-pituitary-adrenal axis. The results indicate that individuals and organs differ in their sensitivity to corticosterone. Moreover, elevated plasma corticosterone may disrupt the acute corticosterone stress response, and may thus reduce the ability of birds to cope with stressors.

The effect of corticosterone-induced stress on amino acid digestibility in Ross broilers

Two experiments (Exp.) were conducted to establish amino acid (AA) digestibility coefficients (DC) for broilers given corticosterone (CS)-induced stress using the apparent ileal digestibility assay. For Exp. 1, 192 Ross x Ross 708 male broilers were placed into 16 floor pens (12 birds/pen). For Exp. 2, 120 Ross x Ross 308 male broilers were placed into 10 floor pens (12 birds/pen). Pens contained nipple drinkers, pan feeders, and soft-wood shavings. Both experiments were completely randomized designs using pen as the experimental unit. In both experiments, chicks were given a common starter diet from d 1 to 20. From d 21 to 30, broilers were provided a control diet or the control + 15 mg of CS/kg of diet dissolved in soybean oil (8 and 5 replications/treatment in Exp. 1 and 2, respectively). Diets were based on corn (65.07%) and soybean meal (26.36%) and contained an indigestible marker (chromic oxide 0.3%). Diets were formulated to contain 3,175 kcal of ME, 18.5% CP, 0.79% digestible TSAA, and 1.00% digestible Lys. Stress validation was accomplished by measuring BW gain, feed intake, and liver weight on d 30. Evidence that stress occurred was apparent due to the fact that broilers fed CS had lower BW gain and higher liver weight than those fed control. On d 30, the ileal contents were removed from 3 birds/pen, pooled, dried, and analyzed for AA content. Amino acid DC were calculated using the following equation: DC = 100 -(dietary marker % x ileal AA %) / (ileal marker % x dietary AA %) x 100. Amino acid digestibility did not differ (P > 0.05) between treatments in either experiment. Based on this research, future research should be directed at establishing DC for other nutrients in stressed broilers or the effect of different nutrients on the stress response.

Impaired development of broiler chickens by stress mimicked by corticosterone exposure

The effects of corticosterone (CORT) administration on the development of muscular tissues of broiler chickens (Gallus gallus domesticus) fed with diets differing in lipid content were investigated. The experimental chickens were given one of two experimental diets: high lipid diet (9.9% crude fat) or control diet, from 21 d of age. At 28 d of age, half of the chickens in each dietary treatment were exposed to CORT treatment, supplemented with 30 mg CORT/kg diet for 12 days, while the other half continued to consume the former diet. The zootechnical parameters were recorded at 21, 28, 35 and 39 d, and a blood sample was obtained from 8 birds of each group, respectively. The growth performance of broiler chickens was significantly depressed by CORT administration, but not by dietary treatment. Corticosterone treatment resulted in enhanced energy expenditure. The results indicate that the development of breast muscle was more susceptible to stress mimicked by CORT administration. The results suggest that corticosterone administration enhanced hepatic fatty acid synthesis and resulted in the redistribution of energy to abdominal store from peripheral tissues. Diet rich in lipid content was favorable to the central fat deposit in stressed broiler chickens.

Oxidative stress induced by corticosterone administration in broiler chickens (Gallus gallus domesticus)

Two trials were conducted to evaluate the effects of short-term administration of corticosterone (CORT) on the induction of oxidative injury in broiler chickens (Gallus gallus domesticus). Twelve broiler chickens of 30 and of 40 days of age were respectively employed in Trial 1 and 2. Half of the chickens were administered subcutaneously with CORT (4 mg/kg body weight [BW] in corn oil), while another half served as controls (corn oil) in each trail. In Trial 1, a blood sample was obtained from each chicken immediately before administration and at 1 and 3 h after injection. In Trial 2, the liver and heart were obtained after 3 h of CORT exposure. Short-term administration of CORT resulted in enhanced proteolysis and gluconeogenesis. There were no obvious changes in lipid peroxidation status of the heart and liver, whereas a decrease in lipid peroxidation in the plasma was observed after acute CORT exposure. The significantly increased plasma nonenzymatic antioxidants (uric acid [UA] and total antioxidant capacity) in concert with the enhanced enzymatic antioxidant activity (SOD in heart) during short-term CORT administration indicate preventive changes to counteract the oxidative injury, and these may be tissue specific.

Free diet selection by broilers as influenced by dietary macronutrient ratio and corticosterone supplementation. 1. Diet selection, organ weights, and plasma metabolites

Male broiler chickens (aged 21 d) were allowed to chose freely for 14 d between three diets in which only one specific macronutrient (protein, lipid, or carbohydrate) was isocalorically substituted for one other macronutrient, but otherwise (nearly) isocaloric and composed of the same ingredients. The three diets were low protein (LowCP; 15.81% CP; 6.56% lipid; 50.78% carbohydrate), low lipid (LowL; 19.63% CP; 3.01% lipid; 51.12% carbohydrate), and low carbohydrate (LowCHO; 19.50% CP; 7.72% lipid; 44.00% carbohydrate). The chickens either received 0, 30, or 45 mg of corticosterone (CORT) per kg diet. As a percentage of their total intake, unsupplemented chickens consumed 24.0, 71.4, and 4.6% of the LowCP, LowL, and LowCHO diets, respectively, giving a total CP, L, and CHO intake of 282, 61, and 765 g, respectively. The addition of CORT significantly changed the diet selection, as compared to the unsupplemented chickens, CORT chickens consumed a greater percentage from the LowCP (35%), less from the LowL (55%), and again more from the Low-CHO (10%) diet. On the other hand, total feed consumption, macronutrient, and ME intake were not altered significantly by CORT supplementation, probably because of the close similarity of the diets. Corticosterone-supplemented chickens manifested hyperglycemia, hyperlipidemia, and uric acidemia suggesting insulin resistance, increased lipogenesis and protein catabolism, respectively. The elevated plasma creatine kinase (CK) activities of CORT chickens are also suggestive for decreased muscle cell membrane stability. Furthermore, CORT chickens were characterized by increased proportional weights of liver, abdominal fat pad, proventriculus, and gizzard, whereas an involution of spleen and bursa was observed. In conclusion, the present results suggest that high circulating levels of CORT as in the case of stress results in metabolic alterations, which in turn, affects diet preference as a compensatory mechanism to adapt energy and nutrient metabolism.

Glucocorticoids and parental hyperphagia in ring doves (Streptopelia risoria)

These studies explored the possibility that glucocorticoids promote parental care in ring doves by mediating, at least in part, the pronounced increase in food consumption that parent doves exhibit while provisioning their young. Plasma concentrations of the endogenous glucocorticoid corticosterone were found to be significantly higher in breeding females during the posthatching phase than during the incubation period. These differences were not observed in male breeding partners, but sex differences in daily activity rhythms are well documented in breeding doves, and blood sampling at different times of day would be required to adequately characterize the pattern of corticosterone in males during these breeding stages. In studies on nonbreeding doves, twice-daily intracerebroventricular (icv) injections of the synthetic glucocorticoid dexamethasone (DEX) increased food intake by 25-50% in both sexes, and further studies in males revealed that the increase was directly related to the dose of DEX administered. The highest dose of DEX given icv (1.0 microg/day) was not effective in stimulating feeding when given systemically, thereby suggesting that the hyperphagic action of DEX is exerted directly on the central nervous system. The icv infusion of the selective glucocorticoid receptor antagonist RU38486 blocked the hyperphagic effects of twice-daily icv injections of DEX in both sexes. Collectively, these data support the hypothesis that corticosterone contributes to the parental hyperphagia exhibited by breeding doves during the posthatching period. They also suggest that these orexigenic effects are mediated in part by CNS binding sites that resemble mammalian glucocorticoid receptors.

Involvement of corticosterone in food intake, food passage time and in vivo uptake of nutrients in the chicken (Gallus domesticus)

To evaluate the effect of corticosterone on nutrient transport, 10-week-old male chickens were grouped in 4 categories and treated as follows: sham-operated, adrenalectomised, corticosterone (4 mg/kg injected subcutaneously for 5 d) in both sham-operated and adrenalectomised. The food intake, food passage time and uptake of calcium, phosphorus and glucose were determined by standard procedures. Corticosterone administration to both sham-operated and adrenalectomised groups stimulated significantly higher food intake, delayed food passage time and increased uptake of calcium, phosphorus and glucose, as compared to sham-operated control and adrenalectomised groups. Corticosterone administration increased absorption of these nutrients significantly more in the adrenalectomised group than in the sham-operated controls. Corticosterone also significantly elevated the plasma concentrations of these nutrients. The responses to the hormone were significantly greater in adrenalectomised birds. It is concluded that corticosterone increases food intake and retention and the absorption of calcium, phosphorus and glucose in the alimentary tract.