Model of physiological stress in chickens 2. Dosimetry of adrenocorticotropin

Cage-Free Pullets Minimally Affected by Stocking Density Stressors

Management choices during the pullet phase can affect behavior, welfare, and health later in life, but few studies have evaluated the pullet phase, particularly in extensive housing systems. This study was a 2 × 2 factorial randomized complete block design (RCBD) with two strains and two stocking densities. The Lohmann LB-Lite and Lohmann LSL-Lite were housed on the floor at high-stocking density (619-670 cm2/bird) and low-stocking density (1249-1352 cm2/bird), which changed with age from 2 to 16 weeks of age (WOA). Bird-based measures of appearance, blood parameters, organ measurements, and production values were evaluated. Stocking density alone affected (p < 0.05) only relative bursal weight (% of body weight)-3.32% in the low-density versus 3.08% in the high-density group. High-stocking density was correlated with decreased uniformity (high-89.33 ± 0.24%; low-90.41 ± 0.24; p < 0.02) and worse feather coverage in the brown strain. High-stocking density was correlated with greater uniformity (High-90.39 ± 0.24%; Low-88.47 ± 0.24%; p < 0.001) and better feather coverage in the white strain. This study's feed conversion ratio (FCR) was improved by 0.07 in the low-stocking density for both strains. The remaining parameters were affected by strain and age only. Thus, while stocking density effects vary slightly depending on the strain used, cage-free pullets had limited negative effects at both the high and low-stocking densities tested in this study; there were few to no changes in the numerous bird-based welfare parameters tested.

Production performance, haematological parameters, serum biochemistry, and expression of HSP-70 in broiler chickens fed dietary ascorbic acid during heat stress

An experiment was carried out to assess the efficacy of supplemental ascorbic acid (AA) on broiler chicken production performance, blood haematological profile, biochemical profile, and carcass traits under heat stress conditions. A total of 192-day-old broiler chicks were divided into four groups, each with six replicates of eight each (4 × 6 × 8). Four corn-based dietary treatments were formulated: T1 (control diet), T2 (T1 + AA at 200 mg/kg), T3 (T1 + AA at 400 mg/kg), and T4 (T1 + AA at 600 mg/kg) for a period of 42 days. Despite the high temperature and humidity, the 600 mg AA supplemental groups (T4) gained significantly (P ≤ 0.05) more body weight and had a higher feed intake and better feed conversion ratio (FCR) than the control group (T1). After 28 days of feeding the three AA-supplemented diets, antibody titres (humoral immune response) were significantly higher (P ≤ 0.05). The response to intradermally injected phyto-haemagglutinin (PHA-P), an index of the in vivo cell-mediated immune response, was found to be increased (P ≤ 0.05) in the 400 and 600 mg AA-supplemented groups after 35 days. Higher levels of AA (T4) supplementation significantly (P ≤ 0.05) improved haematological values such as haemoglobin (Hb), total erythrocyte count (TEC), total leukocyte count (TLC), and differential leukocyte count (DLC), heterophil:lymphocyte (H:L) in comparison to the control group (T1). The supplemented group improved the serum biochemical profile of the birds, with an increase (P ≤ 0.05) in total serum protein, albumin, and globulin and a decrease in serum cholesterol and corticosterone levels in the T4 group compared to the control group. Heat shock protein-70 (HSP-70) was gradually elevated after increasing the ascorbic acid concentration (P ≤ 0.05) at 14 and 21 days. As a result, it can be concluded that supplementing ascorbic acid at 600 mg/kg is beneficial for improving the performance, immunity, and blood haematological biochemical profile and upregulating the HSP-70 gene of broiler chickens under heat stress conditions.

Effects of different stocking densities on organ development, blood biochemical indices, and antioxidative status of breeder pigeons during the rearing period

The present experiment was conducted to investigate the effect of different stocking densities on the organ development, blood biochemical indices, and antioxidative status of breeder pigeons during the rearing period. A total of 280 (half male and half female) 40-day-old young pigeons were allocated into 4 groups, including 3 experimental groups (in compartments of the flying room): the high stocking density (HSD) (0.308 m3/bird), standard stocking density (SD) (0.616 m3/bird), and low stocking density (LSD) (1.232 m3/bird) and a caged control (0.04125 m3/bird). The results showed that the contents of corticosterone and heat shock protein 70 in males and the corticosterone content in females were higher in the control than in the other groups. The relative weight of liver, lung, and gizzard in males of the HSD group was the highest among the 4 treatments, whereas the abdominal fat index in the control group was higher than those in the other 3 treatments. Body weight and the relative weight of liver and abdominal fat in female pigeons in HSD group increased significantly. The levels of serum urea nitrogen and uric acid in pigeons of LSD group increased significantly, while the concentration of total cholesterol and the activity of alanine aminotransferase were higher in the control group. Ion (K+, Ca2+, and Na+) concentrations in female pigeon serum were also elevated in the control. The activity of antioxidant enzymes, including the total antioxidant capacity, superoxide dismutase, and glutathione peroxidase in pigeon breast muscle and liver had different degrees of inhibition when the space room was crowded. Moreover, the level of malondialdehyde in the liver of male caged pigeons was higher than that in the other treatments. In summary, rearing in cages or at a high density caused stress responses in the breeder pigeons. The stocking density of breeder pigeons during the rearing period should be ranged from 0.616 m3/bird to 1.232 m3/bird.

Gamma-amino butyric acid (GABA) supplementation alleviates dexamethasone treatment-induced oxidative stress and inflammation response in broiler chickens

This experiment was conducted to investigate the effect of Gamma-amino butyric acid (GABA) on growth performance, serum and liver antioxidant status, inflammation response and hematological changes, in male broiler chickens under experimentally induced stress via in-feed dexamethasone (DEX). A total of 300 male chicks (Ross 308) on day 7 after hatching, were randomly selected into four groups which were positive control group (PC, without any treatment), negative control (NC, with 1 mg/kg DEX), a third group received 1 mg/kg DEX and 100 mg/kg GABA (DG ⁺) and the last one was (DG ⁺⁺) which received 1 mg/kg DEX and 200 mg/kg GABA. Each group has five replicates (15 birds/replicate). Dietary GABA modulated DEX-induced adverse effects on body weight, feed intake, and feed conversion ratio. The DEX-induced effect of serum levels of IL-6 and IL-10 was reduced by dietary GABA supplementation. The activity of serum and liver superoxide dismutase, catalase, glutathione peroxidase were enhanced and malondialdehyde was reduced by GABA supplementation. The serum levels of total cholesterol & triglyceride were higher while low-density lipoprotein & high-density lipoprotein were lower in GABA groups than NC group. GABA supplementation also significantly decreased the heterophil, heterophil/lymphocyte ratio and elevated the activities of aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) than NC group. In conclusion, dietary GABA supplementation can alleviate DEX stress-induced oxidative stress and inflammation response.

Characterization of the chicken melanocortin 5 receptor and its potential role in regulating hepatic glucolipid metabolism

Melanocortin receptors (MC1R-MC5R) and their accessory proteins (MRAPs) are involved in a variety of physiological processes, including pigmentation, lipolysis, adrenal steroidogenesis, and immunology. However, the physiological roles of MC5R are rarely characterized in vertebrates, particularly in birds. In this work, we cloned the full-length cDNA of chicken MC5R and identified its core promoter region. Functional studies revealed that cMC5R was more sensitive to ACTH/α-MSH than β-MSH/γ-MSH, and was coupled to the cAMP/PKA signaling pathway. We demonstrated that MRAP2 decreased MC5R sensitivity to α-MSH, whereas MRAP1 did not have a similar effect, and that both MRAPs significantly reduced MC5R expression on the cell membrane surface. Transcriptome and qPCR data showed that both MRAP1 and MC5R were highly expressed in chicken liver. Additionally, we observed that ACTH might increase hepatic glucose production and decrease lipogenesis in primary hepatocytes, and dose-dependently downregulated the expression levels of ELOVL6 and THRSPA genes. These findings indicated that ACTH may act directly on hepatocytes to regulate glucolipid metabolism, which will help to understand the function of MC5R in avian.

Determination of selected biochemical parameters in blood serum and egg quality of Czech and Slovak native hens depending on the housing system and hen age

The objective of this study was to determine and evaluate the impact of the age and housing system on blood indicators (triacylglycerides, total cholesterol, aspartate aminotransferase, total proteins, albumin, glucose) and physical egg quality parameters (egg weight, shape index and surface area, eggshell proportion, thickness, strength, and color, albumen proportion and index, Haugh units, yolk proportion, index and yolk-to-albumen ratio) in selected native breeds of the Czech Republic (the Czech Golden Spotted hens) and Slovakia (the Oravka hens). Furthermore, the concentration of cholesterol in the yolk was determined. A total of 132 animals were used. There were 60 eggs collected from each breed at each monitored period for the evaluation of egg quality. Blood samples were taken by puncture of a wing vein. The assessments were made when the hens were of 34, 42, and 50 weeks old. Enriched cages and floor pens with litter were used as housing systems. The effects of breed, housing system, and age were observed. Furthermore, interactions among these factors were calculated. The significant effect of housing system was found in total cholesterol (P = 0.098) and aspartate aminotransferase (P = 0.0343) and the significant effect of age in total protein (P = 0.0392). The significant effect of breed (P = 0.0199), housing system (P = 0.0001), and age (P = 0.0001) was found in concentration of cholesterol in the yolk. Regarding the egg quality, the significant effect of breed (P = 0.0001) was found in eggshell color, albumen index and Haugh units, whereas the significant effect of housing system was found in egg weight (P = 0.0002), egg surface area (P = 0.0003), eggshell proportion (P = 0.0460), thickness (P = 0.0216), strength (P = 0.0049), and color (P = 0.0009). The significant effect of age was determined in all parameters except for the eggshell proportion and strength. The results represent an interesting comparison of changes in biochemical blood and egg quality parameters. It is necessary to further evaluate these indicators, especially in other genetic resources of hens, where the data are often nonexisting.

Chitosan oligosaccharide supplementation alleviates stress stimulated by in-feed dexamethasone in broiler chickens

This experiment was conducted to investigate the effect of dietary chitosan oligosaccharide (COS) on growth performance, nutrient digestibility, jejunal morphology, gene expression, and plasma antioxidant enzymes in male broiler chickens under experimentally induced stress via in-feed dexamethasone (DEX). On day 3 after hatching, male broiler chicks were assigned to 2 diets supplemented with COS at 0 or 1 g/kg in a randomized complete block design and fed to day 27 after hatching. Birds were pooled within each diet (0 or 1 g/kg COS) to equalize the average BW and fed 2 diets supplemented with 0 or 1 g/kg DEX, within each dietary COS, from day 20 to 27 after hatching. This resulted in a 2 × 2 factorial arrangement of treatments with 2 levels each of COS and DEX, 8 replicate cages of 7 birds per cage. On day 27 after hatching, birds were weighed and euthanized, and samples were collected. Dietary COS decreased (P < 0.05) DEX-induced effects (interaction; P < 0.05) on BW, BW gain, and gain:feed. Dietary COS supplementation attenuated the DEX effects (interaction; P < 0.05) on villus height, crypt depth, villus height to crypt depth ratio, and ileal digestibility of dry matter and energy. The DEX-induced effect of relative mRNA expression of jejunal mucosa IL-6, IL-10, and claudin-1 was reduced by dietary COS supplementation (interaction; P < 0.05). Responses (interaction; P < 0.05) in the activity of plasma superoxide dismutase, catalase, and glutathione peroxidase to COS and DEX were similar to those observed with the relative mRNA expression. Chitosan oligosaccharide supplementation increased (P < 0.05) the mRNA expression of IL-8 and occludin. In conclusion, dietary COS decreased the DEX-induced effect by improving growth performance, nutrient digestibility, jejunal morphology, gene expression, and plasma antioxidant enzymes in broiler chickens. This implies that dietary COS may be useful for ameliorating the negative effect of stress on gut health in broiler chickens.

Elevated levels of the stress hormone, corticosterone, cause 'pessimistic' judgment bias in broiler chickens

Pessimistic judgment biases, whereby humans or non-human animals interpret ambiguous information negatively, are hypothesised to be one of the suite of adaptive changes that comprise the vertebrate stress response. To test this hypothesis, we asked whether experimentally elevating levels of the glucocorticoid stress hormone, corticosterone, in broiler chickens produced a pessimistic judgment bias. We trained young chickens to discriminate a stimulus (paper cone) placed at two locations in an arena, one associated with reward (mealworms) and one with punishment (air puff). During seven days of non-invasive administration of either corticosterone or vehicle control, we tested the birds' responses to the cone placed at ambiguous locations between the trained locations. Corticosterone-treated birds were more likely than controls to respond as if punishment was likely when the cone was placed near to the punished location. The degree of this 'pessimism' was associated with smaller relative spleen weight, which is a documented consequence of chronic stress in chickens. We conclude that changes in corticosterone levels in chickens are sufficient to cause a specific change in decision making, dubbed 'pessimism', whereby corticosterone-treated birds showed an increased expectation of punishment in the face of ambiguous information. Pessimism could be a useful welfare indicator in chickens.

Effects of Graded Dietary L-arginine Supply on Organ Growth in Four Genetically Diverse Layer Lines during Rearing Period

Little information has been available about the influence of genetic background and dietary L-arginine (Arg) supply on organ growth of chickens. Therefore, the present study examined the effects of a graded ad libitum Arg supply providing 70, 100 and 200% of recommended Arg concentration on organ growth of female chickens from hatch to 18 weeks of age. The chickens derived from four layer lines of different phylogeny (white vs. brown) and laying performance (high vs. low). Based on residual feed and absolute body and organ weights recorded in six-week-intervals, feed consumption, changes of relative organ weights and allometric organ growth were compared between experimental groups. Surplus Arg caused higher feed intake than insufficient Arg (p<0.01) that induced growth depression in turn (p <0.05). During the entire trial chicken's heart, gizzard and liver decreased relatively to their body growth (p<0.001) and showed strong positive correlations among each other. On the contrary, proportions of pancreas and lymphoid organs increased until week 12 (p<0.001) and correlated positively among each other. Due to their opposite growth behaviour (p<0.001), internal organs were assigned to two separate groups. Furthermore, insufficient Arg induced larger proportions of bursa, gizzard and liver compared with a higher Arg supply (p<0.05). In contrast to less Arg containing diets, surplus Arg decreased relative spleen weights (p<0.01). The overall allometric evaluation of data indicated a precocious development of heart, liver, gizzard, pancreas and bursa independent of chicken's genetic and nutritional background. However, insufficient Arg retarded the maturation of spleen and thymus compared with an adequate Arg supply. In conclusion, the present results emphasised the essential function of Arg in layer performance, and indicated different sensitivities of internal organs rather to chicken's dietary Arg supply than to their genetic background.

Evaluation of a stress model induced by dietary corticosterone supplementation in broiler breeders: effects on egg yolk corticosterone concentration and biochemical blood parameters

1. This study aimed to evaluate a stress model induced by corticosterone (CORT) supplementation in the diet of broiler breeder hens. 2. A total of 60 Ross broiler breeder hens at 29 weeks of age were randomly divided into 4 groups with 15 hens each. The first group served as the control. The rest of the hens were given 1, 1.5 or 2 mg of CORT/hen/d (CORT1, CORT1.5 and CORT2, respectively) for 7 d. Concentrations of yolk CORT, plasma uric acid, glucose, cholesterol, creatine kinase, heterophil (H):lymphocyte (L) ratio and duration of tonic immobility (TI) were measured at d 3, 5 and 7 of CORT supplementation. The same measurements were repeated at 3, 5 and 7 d after CORT was withdrawn from the diet. 3. There were no significant CORT dose effect on yolk CORT and plasma glucose concentrations. Higher plasma uric acid and H:L ratio was obtained for CORT1.5 and CORT2 than for CORT1. From 3 to 7 d of dietary CORT supplementation, yolk CORT and plasma uric acid concentrations and H:L ratio increased whereas plasma glucose concentration decreased. After CORT was withdrawn from the diet, the H:L ratio remained elevated. The duration of TI and plasma creatine kinase concentration did not change during and after CORT supplementation. 4. Yolk CORT concentration was correlated with plasma uric acid concentration during CORT supplementation. 5. The results suggest that dietary CORT supplementation could be used as a stress model and to evaluate hormone-mediated maternal effects in broiler breeder hens.

Corticosterone regulation of ovarian follicular development is dependent on the energy status of laying hens

Glucocorticoids participate in the arousal of stress responses and trigger physiological adjustments that shift energy away from reproduction toward survival. Ovarian follicular development in avians is accompanied by the supply of yolk precursors, which are mainly synthesized in the liver. Therefore, we hypothesized energy status and hepatic lipogenesis are involved in the induction of reproductive disorders by glucocorticoids in laying hens. The results show that corticosterone decreased the laying performance by suppressing follicular development in energy-deficit state, rather than in energy-sufficient state. In corticosterone-treated hens, the suppressed follicular development was associated with the reduced availability of yolk precursor, indicated by the plasma concentration of VLDL and vitellogenin and the decreased proportion of yolk-targeted VLDL (VLDLy). Corticosterone decreased the expression of apolipoprotein B and apolipoprotein VLDL-II in the liver. A drop in VLDL receptor content and an increase in the expression of tight junction proteins occludin and claudin1 were also observed in hierarchical follicles. The results suggest corticosterone-suppressed follicular development is energy dependent. The decreased apolipoprotein synthesis and VLDLy secretion by liver are responsible for the decreased availability of circulating yolk precursor, and the upregulation of occludin and claudin expression further prevents yolk deposition into oocytes.

Interaction of transport distance and body weight on preslaughter stress and breast meat quality of broilers

1. The objective of the study was to investigate the effect of transport distance on blood metabolites and breast meat quality of broilers slaughtered at different weights. 2. The study was conducted on Ross 308 broilers from 27 different flocks reared under similar conditions. Slaughter weight was classified as <2·0 kg, 2·0-2·4 kg, and >2·4 kg. Transport distance was categorised as short (65 km), medium (115 km) and long (165 km) distance representing 90, 155 and 220 minutes at an average 45 km/h speed, for each slaughter weight. 3. Higher heterophils and heterophil:lymphocyte (H/L) ratios were obtained for broilers transported over a long distance. Long distance transport increased blood albumin, glucose, and triglycerides levels for <2·0 kg broilers, which did not differ from broilers slaughtered at >2·4 kg after long-distance transport. 4. Broilers slaughtered at >2·4 kg after long-distance transport had lower pH(u), and paler and tougher breast meat, than those broilers slaughtered at <2·0 kg after long-distance transport. 5. A negative correlation was obtained between pH(u) and L*, thawing loss and texture. The L* value was negatively correlated with a*; and positively correlated with b*, thawing and cooking losses. 6. It was concluded that the effect of transport distance could not be evaluated independently of slaughter weight. The interaction between transport distance and slaughter weight contributes to preslaughter stress and meat quality.

Breeding for robustness: the role of cortisol

Robustness in farm animals was defined by Knap as 'the ability to combine a high production potential with resilience to stressors, allowing for unproblematic expression of a high production potential in a wide variety of environmental conditions'. The importance of robustness-related traits in breeding objectives is progressively increasing towards the production of animals with a high production level in a wide range of climatic conditions and production systems, together with a high level of animal welfare. Current strategies to increase robustness include selection for 'functional traits', such as skeletal and cardiovascular integrity, disease resistance and mortality in various stages. It is also possible to use global evaluation of sensitivity to the environment (e.g. reaction norm analysis or canalization), but these techniques are difficult to implement in practice. The hypothalamic-pituitary-adrenocortical (HPA) axis is the most important stress-responsive neuroendocrine system. Cortisol (or corticosterone) released by the adrenal cortices exerts a large range of effects on metabolism, the immune system, inflammatory processes and brain function, for example. Large individual variations have been described in the HPA axis activity with important physiopathological consequences. In terms of animal production, higher cortisol levels have negative effects on growth rate and feed efficiency and increase the fat/lean ratio of carcasses. On the contrary, cortisol has positive effects on traits related to robustness and adaptation. For instance, newborn survival was shown to be directly related to plasma cortisol levels at birth, resistance to bacteria and parasites are increased in animals selected for a higher HPA axis response to stress, and tolerance to heat stress is better in those animals that are able to mount a strong stress response. Intense selection for lean tissue growth during the last decades has concomitantly reduced cortisol production, which may be responsible for the negative effects of selection on piglet survival. One strategy to improve robustness is to select animals with higher HPA axis activity. Several sources of genetic polymorphism have been described in the HPA axis. Hormone production by the adrenal cortices under stimulation by adrenocorticotropin hormone is a major source of individual differences. Several candidate genes have been identified by genomic studies and are currently under investigation. Bioavailability of hormones as well as receptor and post-receptor mechanisms are also subject to individual variation. Integration of these different sources of genetic variability will allow the development of a model for marker-assisted selection to improve animal robustness without negative side effects on production traits.

Heritable genome-wide variation of gene expression and promoter methylation between wild and domesticated chickens

BACKGROUND

Variations in gene expression, mediated by epigenetic mechanisms, may cause broad phenotypic effects in animals. However, it has been debated to what extent expression variation and epigenetic modifications, such as patterns of DNA methylation, are transferred across generations, and therefore it is uncertain what role epigenetic variation may play in adaptation.

RESULTS

In Red Junglefowl, ancestor of domestic chickens, gene expression and methylation profiles in thalamus/hypothalamus differed substantially from that of a domesticated egg laying breed. Expression as well as methylation differences were largely maintained in the offspring, demonstrating reliable inheritance of epigenetic variation. Some of the inherited methylation differences were tissue-specific, and the differential methylation at specific loci were little changed after eight generations of intercrossing between Red Junglefowl and domesticated laying hens. There was an over-representation of differentially expressed and methylated genes in selective sweep regions associated with chicken domestication.

CONCLUSIONS

Our results show that epigenetic variation is inherited in chickens, and we suggest that selection of favourable epigenomes, either by selection of genotypes affecting epigenetic states, or by selection of methylation states which are inherited independently of sequence differences, may have been an important aspect of chicken domestication.

Influence of dietary vitamin E and zinc on performance, oxidative stability and some blood measures of broiler chickens reared under heat stress (35 °C)

This study was conducted to determine the effects of vitamin E (αTA; dL-α-Tocopheryl acetate) and zinc (Zn; ZnCl2) on performance, oxidative stability and some blood measures of broiler chickens under normal and hot temperatures. One hundred sixty 10-day-old male chicks were assigned to four groups in four replicates. The birds received two diets, control and enriched with two levels of vitamin E and Zn (100 and 50 mg/kg of diet, respectively) under two ambient temperatures (22 °C and 35 °C). Although the diets enriched with the antioxidant vitamin and element compared with un-enriched diets resulted in the better performance of the birds, significant differences were related to temperature conditions, as the lowest feed conversion ratio (FCR) and the highest body weight (BW) were observed in the group fed the enriched diet under normal temperature. The serum malondialdehyde (MDA), cholesterol (C), triglycerides (TG), glucose (G), total protein (TP), and hematocrit and heterophil: lymphocyte ratio levels were significantly lower in birds reared under 22 °C compared with the group under 35 °C but the hematocrit was not significantly lower in groups fed enriched diets and exposed to normal conditions (P>0.05). It was concluded that a combination of 100 mg of vitamin E and 50 mg of Zn provides the better performance and the least blood C and TG levels accompanying the better oxidative stability in male broilers under normal temperature (22 °C) and that this combination can be considered as a protective strategy in broiler diets for reducing the negative effects of heat stress.

Increased de novo lipogenesis in liver contributes to the augmented fat deposition in dexamethasone exposed broiler chickens (Gallus gallus domesticus)

Effect of dexamethasone (DEX, a synthetic glucocorticoid) on lipid metabolism in broiler chickens (Gallus gallus domesticus) was investigated. Male Arbor Acres chickens (1 wk old, n=30) were injected with DEX or saline for 1 wk, and a pair-fed group was included. DEX administration resulted in enhanced lipid deposition in adipose tissues. Plasma insulin increased about 3.3 fold in DEX injected chickens as against the control and hepatic triglyceride was higher as compared with the pair-fed chickens. In DEX injected chickens, the hepatic activities of malic enzyme (ME) and fatty acid synthetase (FAS) were significantly increased, while the mRNA levels of acetyl CoA carboxylase (ACC), ME, and FAS were significantly up-regulated, compared with the control. Although the mRNA levels of lipoprotein lipase (LPL), peroxisome proliferator-activated receptor-gamma (PPARgamma) and adipose triglyceride lipase (ATGL) genes in adipose tissue were not affected by DEX injection, ME activity and mRNA levels in abdominal fat pad of chickens treated with DEX are higher than those of control chickens. The results indicated that the increased hepatic de novo lipogenesis and in turn, the increased circulating lipid flux contributes to the augmented fat deposition in adipose tissues and liver in DEX-challenged chickens. The results suggest that glucocorticoids together with the induced hyperinsulinemia should be responsible for the up-regulated hepatic lipogenesis.

Effect of Electric Field During Incubation of Eggs on the Immune Responses of Hatched Chickens

The effects of electric field (EF) during incubation of eggs on the immunocompetence of chickens were investigated over a 42-day experimental period. Eggs from a meat-type breeder flock were incubated under EF of 30 kV/m, 60 Hz during the first 18 days of incubation as compared with the control incubation (C). Chickens from the two incubation treatments were fed ad libitum and their immune system were monitored. Measurements were made of body weight (BW), and lymphoid organs weight (thymus, spleen, and bursa of Fabricius (BOF)) of birds at 21 and 42 days of age. Immune systems of birds were tested for specific antibody responses to sheep red blood cell (SRBC) and Newcastle disease vaccine (NDV), in vivo T-lymphocyte proliferation responses to phytohemagglutinin (PHA), and in vitro to concanavalin A (Con-A). EF incubation of eggs did not significantly (P > 0.05) influence BW of bird, absolute weight of lymphoid organs and weight of thymus, and BOF as a percentage of BW of bird (% BW) at 21 and 42 days of age, humoral immune responses as measured by antibody responses to SRBC and NDV, and cell-mediated immune responses as measured by T-lymphocyte proliferation responses to PHA, and Con-A of birds when compared with those of the C treatment. EF incubation of eggs significantly (P < 0.05) increased spleen weight as a % BW at 21 and 42 days of age when compared with those incubated under the C treatment. Birds at 42 days of age had significantly (P < 0.01) higher BW, lymphoid organ weight, and weight of BOF as a % BW, and lower spleen weight as a % BW when compared with those of 21 days of age. It is concluded that the incubation of eggs under EF of 30 kV/m, 60 Hz increased spleen weight as a % BW, without altering cell-mediated and humoral immune responses and, consequently, immunocompetence of meat chickens during the rearing period of 42 days.

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.

Evaluation of models using corticosterone and adrenocorticotropin to induce conditions mimicking physiological stress in commercial broilers

Three experiments (Exp) were conducted to delineate a suitable model for inducing conditions mimicking physiological stress with minimal bird handling. For Exp 1, Ross x Ross 308 male chicks were fed a control diet or a diet containing 5 mg of corticosterone (CS)/kg from d 1 to 7. For Exp 2, Ross x Ross 508 broilers received 1 of 4 dietary treatments: control; control + 4 IU/kg of BW of adrenocorticotropin (ACTH)/d i.m. from d 21 to 27; control + 8 IU/kg of BW of ACTH/d i.m. from d 21 to 27; or control + 15 mg of CS/kg of diet for 14 d from 21 to 35 d of age. In Exp 3, Ross x Ross 308 broilers were fed high or low nutrient density (ND) from 1 to 41 d of age, and 0 or 20 mg of CS/kg of diet from 18 to 21 d of age. Performance parameters (BW gain, feed intake, feed conversion, and mortality) were measured in all 3 experiments. In Exp 1, CS administration significantly decreased BW gain and decreased feed intake and mortality. In Exp 2, although ACTH injection resulted in significantly depressed performance responses relative to the control, CS administration yielded significantly stronger results. In Exp 3, ND and CS interacted (P = 0.04) to affect feed intake from d 0 to 34. Broilers fed diets containing high ND and CS had higher feed intake than broilers fed low ND and CS. From 0 to 21 and 0 to 42 d, CS decreased feed intake. Increased dietary ND improved BW gain and feed conversion in Exp 3. Also, CS decreased and increased BW gain and feed conversion, respectively, during all periods in Exp 3. Dietary addition of CS negatively impacted performance of broilers, and increasing dietary amino acid density did not ameliorate these effects.

Molting in Salmonella enteritidis-challenged laying hens fed alfalfa crumbles. III. Blood plasma metabolite response

The objective of this study was to examine an alfalfa crumble diet as an alternative molt diet and compare the physiological response of hens to the responses of feed-deprived molted hens. Hens >50 wk old were placed into 6 treatment groups (12 hens per group in trial 1 and 10 hens per group in trial 2): nonmolted Salmonella enterica serovar Enteritidis positive (FF+), nonmolted Salmonella Enteritidis negative (FF-), feed withdrawal Salmonella Enteritidis positive (FW+), FW Salmonella Enteritidis negative (FW), alfalfa Salmonella Enteritidis positive (ALC+), and ALC Salmonella Enteritidis negative (ALC-). Each hen in the Salmonella Enteritidis-positive groups was challenged on the fourth day of the study with 1 mL of 10(6)-cfu Salmonella Enteritidis. Blood was collected on d 2, 5, 9, and 12 of the trial. Blood plasma was collected and metabolite concentrations were analyzed for glucose, calcium, cholesterol, uric acid, total protein, and triglycerides. The feed intakes of the FF hens were 4- to 6-fold greater (P <or= 0.05) than those of the ALC birds in both trials. Over the 12 d of molt, the FW+ hens lost more (P <or= 0.05) BW than all other groups except the FW- hens, whereas the FW-, ALC-, and ALC+ hens lost more BW than the FF hen groups. Uric acid concentrations were generally lower in molted hens compared with the FF hen groups during the initial stages of molt. On d 9 of both trials, concentrations of calcium and total protein were higher (P <or= 0.05) in the FF hens than in the other groups. The FF hen groups exhibited higher (P <or= 0.05) concentrations of triglycerides than the FW and ALC groups in both trials on d 5, 9, and 12. Based on the results from these studies, ALC diets can limit some of the potential physiological stress indicators that accompany feed deprivation during an induced molt.

Electrolyte diets, stress, and acid-base balance in broiler chickens

We compared the acid-base balance in broiler chickens provided diets containing 2 dietary electrolyte balances (DEB), and administered with either adrenocorticotropic hormone (ACTH) or saline solution. Diets were moderate (174 mEq/kg) or high (241 mEq/kg) DEB formulated by altering Na-K-Cl based on actual analysis. The experiment was designed as a split plot, with the main unit consisting of 4 treatments and the factorial treatment structure arranged in a completely randomized design. Osmotic pumps delivered 8 IU of ACTH in saline/kg of BW per d for 7 d, or the same saline volume as used in ACTH at 1 microL/h for 7 d was implanted on d 35. Venous blood samples were collected on d 35 before the pumps were implanted and on d 42 and 49. Birds fed the high DEB diet exhibited significantly higher Na(+) and Ca(2+) levels than birds provided the moderate DEB diet on d 35. Infusion of ACTH significantly increased (P < or = 0.05) hematocrit, hemoglobin, partial pressure of CO(2) (pCO(2)), corticosterone, osmolality, and HCO(3)(-) and reduced pH, BW, partial pressure of O(2) (pO(2)), and plasma concentrations of Na(+) and Cl(-) in both diets compared with the control group on d 42. Similarly, the ACTH treatment significantly increased hematocrit, hemoglobin, Ca(2+), corticosterone, and osmolality and reduced (P < or = 0.05) pO(2), glucose, and BW on d 49. The diet formulated for high DEB partially lowered pCO(2) on d 42. Significant DEB x ACTH interactions were observed for pCO(2) and pO(2) on d 49. However, there was a reduction in pO(2) along with a concomitant increase in erythropoiesis under the ACTH treatment for both diets, compared with the saline control, because of the increased need for O(2) to support gluconeogenic energy production. This adaptive response provided greater numbers of erythrocytes and thus a higher amount of circulating hemoglobin to deliver O(2) for metabolism. The diet formulated for high DEB partially attenuated the adaptive stress condition in broiler chickens.

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.

The effects of feed restriction on plasma biochemistry in growing meat type chickens (Gallus gallus)

The effect of feed restriction on plasma hormones (triiodothyronine - T(3), thyroxine - T(4), and corticosterone), protein, lipid, carbohydrate, and mineral metabolism and activity of plasma enzymes (creatine kinase, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase) were studied in meat type female chickens (Gallus gallus). Ad libitum fed birds were compared with those subjected to severe and moderate quantitative feed restriction from 16 to 100 days of age. Feed restriction elevated plasma T(4) and corticosterone levels and reduced T(3). A feed restriction-induced decrease was observed for plasma protein and albumin concentrations, but not for uric acid and creatinine. Total plasma lipids, triacylglycerols, cholesterol, high density lipids, and calcium were lower for the feed restricted chickens, in particular during the latter phase of the experiment. Concentrations of glucose and phosphorus were not altered by feeding treatment. Activity of alkaline phosphatase was significantly increased in restricted chicks from day 58. Significant changes of plasma biochemical parameters induced by severe and moderate quantitative feed restriction illustrate that limiting feed intake poses an intensive stress on meat type chickens during the rapid growth period. However, activities of creatine kinase, aspartate aminotransferase, and alanine aminotransferase were significantly higher in ad libitum fed chickens during this period. This elevation in enzymatic activity may be in response to tissue damage, indicating potential health and welfare problems also in ad libitum fed meat type chickens, resulting from selection for intensive growth.

Stress and acid-base balance in chickens

Two trials were conducted to study the effects of continuous infusion of adrenocorticotropic hormone (ACTH) on acid-base balance in broiler chickens. Osmotic pumps delivered 8 IU of ACTH in saline/kg of BW/d for 7 d or the same saline volume as used in ACTH at 1 microL/h for 7 d. Blood samples were taken on d 0 (baseline values) and on d 4, 7, and 14 after onset of the infusions. The ACTH treatment increased the hematocrit, partial pressure of CO2, anion gap, corticosterone, mean corpuscular hemoglobin concentration, the blood concentrations of hemoglobin and HCO3-, and reduced the partial pressure of O2, plasma concentrations of Na+, K+, and Cl-. Blood pH values and plasma concentrations of Ca2+ were unaffected by ACTH treatment. The ACTH infusion also resulted in a significant increase in plasma glucose, cholesterone, high-density lipoprotein, and triglyceride. There were no differences in any of the blood constituents measured from control groups. Results indicate that infusion of ACTH resulted in changes in plasma acid-base status along with changes in other blood metabolic variables. However, the ACTH treatment did not prevent homeostatic regulation of acid-base balance, as indicated by constant blood pH. There was, however, an increased need for O2 to support gluconeogenic energy production; the birds responded by increased erythropoiesis. This adaptive response provided greater numbers of erythrocytes and thus a higher amount of circulating hemoglobin to deliver O2 for metabolism.

Stocking Density and Physiological Adaptive Responses of Broilers

Three trials were conducted to assess the effects of stocking density on physiological adaptive responses of broilers. Male broilers were reared in floor pens under conditions similar to those used commercially in the United States. Accepted indicators of adaptation to a stressor were measured on d 49 including plasma concentrations of corticosterone, glucose, cholesterol, and total nitrites as an indicator of nitric oxide, as well as heterophil:lymphocyte ratio. In trial 1, calculated stocking densities were 20, 25, 30, 35, 40, 45, 50, and 55 kg of BW/ m2 and in trials 2 and 3, stocking densities were 30, 35, 40, and 45 kg of BW/m2. Stocking densities were calculated based on a final BW of 3.3 kg. Linear trend analyses were used to assess the role of stocking density on each of the physiological parameters. Results indicate that stocking density did not cause physiological adaptive changes indicative of stress.

Stocking density effects on male broilers grown to 1.8 kilograms of body weight

This study examined the effects of stocking density on live performance, physiological stress level indicators, and processing yields of male broilers grown to 1.8 kg. A total of 3,120 Ross x Ross 708 male chicks was placed into 32 floor pens (5.57 m2/pen). Stocking density treatments were 25, (75 birds/pen), 30 (90 birds/ pen), 35 (105 birds/pen), and 40 (120 birds/pen) kg of BW/m2. The BW gain, feed consumption, and feed conversion were adversely affected with increasing stocking densities by 35 d. Physiological stress indicators (plasma corticosterone, glucose, cholesterol, total nitrites, and heterophil:lymphocyte) were not affected. Litter moisture was higher as stocking density increased, which led to higher footpad lesion scores. In parallel to growth responses, carcass weight was depressed by increasing stocking density, but carcass yield, absolute and relative amounts of abdominal fat, and carcass skin defects were not affected. Increasing stocking density decreased breast fillet weight and its relative yield and breast tender weight, but not breast tender yield. As calculated stocking density increased 5 kg of BW/m2 beyond 25 kg of BW/ m2, final BW and breast fillet weight decreased by 41 and 12 g, respectively. We conclude that increasing stocking density beyond 30 kg of BW/m2 adversely affects growth responses and meat yield of broilers grown to 1.8 kg but does not alter physiological stress indicators.

Physiological Stress in Laying Hens

Stress responses in laying hens were mediated by continuous infusion of adrenocorticotropin (ACTH) via osmotic pumps. The ACTH was dissolved in saline solution (0.85%), and each pump delivered 8 IU of ACTH per kilogram of BW per day at the rate of 1 microL/h for 7 d. Control hens received pumps loaded with saline. Measurements were made at 6 d postpump implantation, unless otherwise indicated. The ACTH-treatment increased BW and total carcass, rear half of carcass, intestinal, and liver weights. Proximate analyses of liver showed increases in dry weight, moisture, protein, fat, carbohydrate, and ash content. Weights of the front half of the carcass, as well as weights of the abdominal fat pad, heart, head, feet, and skin were unaffected by ACTH-treatment. Plasma corticosterone, glucose, cholesterol, and high-density lipoproteins were increased by ACTH, whereas triglycerides were decreased. Feed and water intake, total excreta, and excretory DM were all increased in ACTH-treated hens. The ACTH decreased carbohydrate in excreta, whereas ash, protein, fiber, and gross energy of excreta were unaffected. The ACTH did not affect digestibility of dry matter, proteins, carbohydrates, fats, or gross energy; however, absorption of ash, protein, carbohydrates, and gross energy were increased by ACTH. Antibody levels to sheep red blood cells, cell-mediated immunity (wattle index to phytohemagglutinin-phosphate), and relative spleen weight were reduced by ACTH, whereas heterophil:lymphocyte ratio was increased. Reproduction in hens was negatively affected by ACTH treatment, as measured by cessation of laying on the third day of treatment, atretic follicles, and decreased oviduct weight.

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.

Corticosterone and insulin interact to regulate plasma glucose but not lipid concentrations in molting starlings

Captive starlings (Sturnus vulgaris) undergoing a prebasic molt were given exogenous insulin (INS) and corticosterone (CORT), to determine how these counterregulatory hormones would affect glucose and triglyceride concentrations during stress. Experiments were conducted at both morning (11:00) and night (23:00) to monitor daily variation in these responses. Concentrations of CORT, glucose, and triglycerides were measured in blood plasma within 3 min of disturbance (basal) and at 40, 70, and 150 min thereafter (stress-induced) to monitor the effect of injecting saline, INS, CORT, or INS+CORT. Saline injection (which included the stress of handling and restraint) increased CORT concentrations, decreased triglycerides, but had no effect on circulating glucose. Daily variation was not evident in CORT or glucose, but concentrations of triglycerides were higher at night than during the day. INS markedly suppressed glucose concentrations, but had no effect on plasma CORT or triglycerides. Glucose levels did not change in response to stress, but exogenous CORT elicited hyperglycemia during the day. Injected CORT also hastened the recovery of glucose concentrations from INS-induced hypoglycemia at night, and had no effect on circulating triglycerides. Basal concentrations of CORT, glucose, and triglycerides exhibited photoperiodic (mimicking seasonal) changes when combined with data from an earlier study in starlings held on long- and short-day photoperiods. During the prebasic molt, all three measurements were lower compared to other photoperiods. Together, these data suggest that glucose and triglycerides concentrations are regulated differently during molt, but INS and CORT maintain their traditional effects.

Stress and nutritional quality of broilers

Broiler chicks were reared in environmental chambers. All birds were started under ideal conditions, i.e., 30.6 C with 35% RH. Beginning at Day 36, half of the chicks were maintained at 24 C and 35% RH. The other half were subjected to a cyclic temperature-RH regime that approximated a typical August day in central Mississippi (heat treatment). Half of each of the described groups received implants of osmotic pumps that released adrenocorticotropin (ACTH) at 8 IU/kg BW/d for 7 d. The remaining birds received placebo pumps. The main effects of ACTH and heat treatments were similar. Both treatments caused reductions in BW, carcass weight (CW), carcass protein (CP), and muscle calorie (C) content. ACTH, but not heat, reduced carcass moisture (M). Carcass fat and ash, however, were not affected. Most changes were not reversed after 1 wk of recovery. Although visible signs of pale, soft, exudative muscle (PSE) were present, "white" areas of muscle were absent. The decreased meat yield and detrimental changes in meat quality suggest that stress, whether induced hormonally or by exposure to over-heating, caused losses that were as severe as those associated with PSE under field conditions.

Model of physiological stress in chickens 5. Quantitative evaluation

Physiological stress was studied in broilers using a new model employing continuous release of adrenocorticotropin (ACTH). A total of 42 adaptive response parameters were evaluated. A treatment response ratio, P-value transformation, and stress score were determined for each parameter. The treatment response ratio was calculated by dividing the maximum response of the ACTH-treated birds for each parameter by the average response of control (CON) birds in all cases in which maximum response of ACTH-treated birds exceeded the average response of CON. This treatment response ratio is designated hereafter as ACTH/CON ratio. In those cases in which average response of CON exceeded maximum response of ACTH-treated birds, the reciprocal equation was employed (i.e., CON/ACTH ratio). Probability value transformations were determined by transforming P-values as follows: NS P-values or those exhibiting significance at values less than probability of 5% were expressed as P<0.05 = 1, P-values exhibiting significance between 0.05 and 0.02 were expressed as P at 0.05 to 0.02 = 2, and P-values exhibiting significance at probabilities of 1% or less were P<0.01 = 4. Each stress score was calculated as treatment response ratio times P-value transformation. The 42 response parameters were assigned to one of four adaptive categories, and these were morphologic, endocrine, and blood metabolites; digestion and metabolism; and reticuloendothelial responses. The endocrine and blood metabolites category had the highest average of the four stress response categories, and five of the top ten parameters were found in this category.

Model of physiological stress in chickens 2. Dosimetry of adrenocorticotropin

Continuous adrenocorticotropin (ACTH) delivery by mini-osmotic pumps is a reliable method to induce stress in broilers. The present study was conducted to determine the minimum effective dose of ACTH that will evoke physiological stress. Chicks, which had been reared under floor-pen conditions until 5 wk of age received mini-osmotic pumps by surgical implantation. The mini-osmotic pumps delivered 2, 4, 8, or 16 IU of porcine ACTH/kg BW/d for 7 consecutive d. Controls (CON) were untreated chicks. Continuous infusion of ACTH caused dose-related stress responses. Chicks that received 8 or 16 IU showed the greatest responses, whereas those that received 2 or 4 IU were intermediate to the birds dosed with high ACTH and the CON birds. Responses included decreased BW; decreased relative weights of the bursa of Fabricius, thymus, and spleen; and increased relative liver weight. Concomitantly, increased liver lipid and decreased liver moisture were recorded. Plasma concentrations of corticosterone (CS), glucose (GLU), total protein (TP), cholesterol (CHOL), and triglycerides (TRI) and the ratio of heterophils to lymphocytes were increased during ACTH infusion. ACTH infusion at 8 IU/kg BW/d for 7 d was determined to be the minimum effective dose that caused physiological stress in broilers.

Model of physiological stress in chickens 3. Temporal patterns of response

The temporal pattern of stress responses following continuous infusion of adrenocorticotropic hormone (ACTH; 8 IU/kg BW/d for 7 d) in broilers was determined in two experiments. Results indicate that the order of responses were elevated plasma corticosterone (CS) by 2 h, elevated plasma glucose (GLU) by 12 h, increased liver weight concomitant with increased hepatic lipid and decreased liver moisture by 18 h, decreased relative weight of the spleen by 24 h, elevated heterophil/lymphocyte (H/L) ratio by 2 d, decreased body weight and relative weights of the bursa of Fabricius and thymus by Day 4, and decreased liver soluble protein content by 12 d.

Model of physiological stress in chickens 4. Digestion and metabolism

Two similar experiments were conducted to evaluate the effects of stress on growth and feed utilization of broiler chicks. Stress was induced by continuous delivery of adrenocorticotropin (ACTH) at 8 IU/kg BW/d for 7 consecutive d. During the 7-d stress period, ACTH-treated chicks did not exhibit increases in feed intake, but increases in water intake concomitant with an increase in excreta output were recorded. The ACTH caused decreases in digestion of dry matter, proteins, gross energy, and carbohydrates, whereas fat digestibility was unaffected. Digestion of these nutrients was affected more than absorption during the stress period. By 1 wk poststress, all parameters were comparable with those of the control, except for feed intake, which was less than that of CON. The BW of ACTH-treated chicks were lower than CON through 1 wk after cessation of infusion of ACTH. Contrasted to effects during the stress period, after cessation of ACTH-treatment, absorption of all nutrients was reduced, and, during this poststress recovery period, digestion appeared to return to the range of CON values. Results indicate that all physiological parameters with the exceptions of reductions in BW and thymus weight returned to the range of CON values within 1 wk after cessation of ACTH infusion. However, feed intake and absorption of energy dry matter and nitrogenous compounds remained lower than CON at that time. Also, losses in skeletal muscle caused by prolonged gluconeogenesis apparently required extended periods for complete recovery, as evidenced by stressed chicks that did not gain comparably to CON after a 1 wk cessation of ACTH delivery.