Yolk Corticosterone Concentrations Research Articles

Nutritional and physiological responses to dietary phosphorus levels and phytase in pullets and laying hens

The objective of this study was to determine the effects of dietary available phosphorus (P) levels and dietary phytase added into the very low-P diet on the performance, mineral balance, odor emission, and stress responses in growing pullets and laying hens during 13 to 32 wk of age. One hundred sixty-eight pullets (Hy-Line Brown) were randomly assigned into 1 of 4 dietary treatments with 7 replicates of 6 birds each. Experimental diets were formulated to contain 3 graded P levels at 0.25, 0.35, and 0.45% during 13 to 15 wk (phase 1), 0.25, 0.35, and 0.45% during 16 to 18 wk (phase 2), and 0.20, 0.30, and 0.40% during 19 to 32 wk (phase 3). In addition, dietary phytase (500 FTU/kg matrix values) was added into the very low-P diets (0.20% during 13-15 wk, 0.25% during 16-18 wk, and 0.20% during 19-32 wk) to meet the nutritional adequacy with standard P diets. In all phases, decreasing dietary P levels did not affect (P > 0.05) growth, laying performance, and egg qualities. Decreasing dietary P levels linearly increased the relative duodenal and oviduct weights (P < 0.05), and quadratically increased the relative ovary weight in pullets (P = 0.016). Dietary phytase lowered (P = 0.021) the relative duodenal weight compared with the very low-P diet. Tibia breaking strength and tibia Mg contents in pullets were linearly lowered (P < 0.05) as dietary P levels decreased. Dietary phytase tended to increase (P = 0.091) tibia breaking strength and significantly increased (P = 0.025) tibia Mg content compared with the very low-P diet. Dietary P levels and dietary phytase affected (P < 0.05) ileal crypt depth and ileal villus height: crypt depth ratio in pullets. Decreasing dietary P levels linearly decreased (P < 0.01) crude fat digestibility and P excretion in both pullets and laying hens. Dietary phytase reversed (P < 0.05) the very low-P diet-mediated decrease of crude fat digestibility in pullets and laying hens. Dietary P levels and dietary phytase affected (P < 0.05) odor emission including ammonia in pullets and total volatile fatty acids in laying hens. Finally, lowering dietary P levels increased (P < 0.01) yolk corticosterone concentrations and the increased corticosterone concentration by the very low-P diet was reversed by dietary phytase. Collectively, our study shows that decreasing dietary P levels induced nutritional and physiological responses in pullets and laying hens and these P-mediated negative effects were mitigated by dietary phytase.

Impact of relative humidity on the laying performance, egg quality, and physiological stress responses of laying hens exposed to high ambient temperature.

The present study investigated the effects of relative humidity (RH) on the laying performance, egg quality, and stress indicators of laying hens raised at high ambient temperatures. A total of 180 Hy-Line Brown laying hens (68-wk-old) were randomly allotted to one of the following three RH conditions for 12h a day (9:00 a.m.-9:00 p.m.) over four weeks: low RH (LRH; 25% RH), moderate RH (MRH; 50% RH), and high RH (HRH; 75% RH); ambient temperature was 30°C under all treatments. None of the RH treatments affected hen-day egg production, egg weight, or egg mass (P>0.05). However, feed intake was lower in the HRH group than in the LRH group (P<0.05). Plasma corticosterone (CORT) concentration on day 21, yolk CORT concentration on day 3, and albumen CORT concentration on day 7 following RH exposure were higher in the HRH group than in the LRH group (P<0.05). Moreover, plasma HDL-cholesterol concentration on day 14 was higher in the HRH group than in the LRH group (P<0.05). On days 3 and 14, the Haugh unit decreased (P<0.05) in the LRH group compared with that in the MRH and HRH groups. The HRH-exposed laying hens showed the lowest (P<0.05) eggshell thickness on day 14. The absolute weights of eggshell, yolk, and albumen decreased in the HRH group compared with those in the MRH and LRH groups. Overall, high RH lowered feed intake and egg quality except for the Haugh unit, and induced stress response as manifested by elevated plasma, yolk, and albumen CORT concentrations. To our best knowledge, the present study is the first to demonstrate the role of RH in triggering temperature stress responses in laying hens.

The relation between liver damage and reproduction in female Japanese quail (Coturnix japonica) exposed to high ambient temperature

Reproductive failure associated with heat stress is a well-known phenomenon in poultry. High temperatures also induce various metabolic disturbances in many animals. Because the liver plays a central role in metabolism, the present study aimed to clarify the relationship between liver and reproduction in Japanese quails exposed to high temperatures. In the consecutive 20-D experimental period, quails were treated with 25°C (control) or 34°C (heat) from 12:00 to 16:00. Eggs were collected for hatching. On completion of the experimental period, quails were humanely euthanized for hormone analyses (e.g., serum and ovarian follicles). Serum metabolites were analyzed using GC/MS. Liver and ovary samples were collected for mRNA levels, histomorphology, and metabolic analysis. Ovary and oviduct weights significantly decreased after daily heat exposure. The number and weight of hierarchical follicles also decreased. Consequently, egg weight decreased. Although there was no difference in fertilization rate, chick birth weight significantly decreased in the heated group. Corticosterone and 17β-estradiol in the serum significantly increased in the heated group. Yolk corticosterone and 17β-estradiol concentration and content were higher in the heated group. Ovary sterologenic enzymes gene P450scc and estrogen receptor expression level increased. The FSH receptor decreased in heat-stressed quails. MetaboAnalyst analysis indicated that high temperature affects propanoate metabolism, beta-alanine metabolism, aspartate metabolism, and histidine metabolism. Triglyceride and cholesterol levels in the liver increased in the heated group. The heated group also had an increased mRNA expression of AGPAT5, apoptosis gene caspase3, and the immunocytokine genes IL-6 and TLR4. However, NF-κB gene expression decreased. These results suggest that high temperatures affect lipid metabolism and apoptosis and cause inflammation in the liver. High temperature induced ovarian dysfunction, which resulted in the decline of hierarchical follicle number and weight, egg weight, and chick birth weight. The increased level of 17β-estradiol suggests liver damage. Protecting liver function from damage may assist quails cope in summer.

Yolk corticosterone in the Gouldian Finch (Erythrura gouldiae)

ABSTRACTMaternal hormones are thought to play an important role in determining the rate of evolutionary adaptation. Previous avian studies have shown that the transfer of maternally derived hormones, such as progesterone and testosterone, to the egg, affects many aspects of offspring development. In contrast, the impact of maternal corticosterone (CORT) is much less studied. CORT, the principal avian glucocorticoid hormone, is thought to be passively transferred to the egg yolk from the maternal plasma. Maternal CORT may play a role in determining the development of young birds by adaptively programming offspring for their environment. We developed a protocol which effectively quantifies yolk CORT concentrations both within and across clutches, using solid-phase extraction and radioimmunoassay. We hypothesised that Gouldian Finch (Erythrura gouldiae) mothers would differ in their yolk CORT concentrations and that maternal condition would relate to absolute yolk CORT deposition. We found variation in yolk CORT concentrations between clutches, whilst yolk CORT increased with egg number in the first breeding season and negatively correlated with yolk mass. Yet, contrary to our predictions, neither maternal mass nor clutch size showed any relationship to yolk CORT concentrations or to egg or yolk mass. Our data suggest that yolk CORT varies with maternal identity for reasons which do not appear to be linked to maternal condition. Further research is needed to determine the link between maternal and egg yolk concentrations at the individual level. Such tests would be valuable for understanding the role of CORT in the reproductive effects previously observed in this threatened species.

Effect of yolk corticosterone on begging in the yellow-legged gull

Behavioral lateralization is widespread across vertebrates. The development of lateralization is affected by both genetic and environmental factors. In birds, maternal substances in the egg can affect offspring lateralization via activational and/or organizational effects. Corticosterone affects the development of brain asymmetry, suggesting that variation in yolk corticosterone concentration may also influence post-natal behavioral lateralization, a hypothesis that has never been tested so far. In the yellow-legged gull (Larus michahellis), we increased yolk corticosterone concentration within physiological limits and analyzed the direction of lateralization of hatchlings in reverting from supine to prone position (‘RTP’ response) and in pecking at dummy parental bills to solicit food provisioning (‘begging’ response). We found that corticosterone treatment negatively affected the frequency of begging and it may cause a slight leftward lateralization. However, the direction of lateralization of the RTP response was not affected by corticosterone administration. Thus, our study shows a maternal effect mediated by corticosterone on a behavioral trait involved in parent-offspring communication during food provisioning events. The findings on lateralization are not conclusive due to the weak effect size but provide information for further ecological and evolutionary studies, investigating mechanisms underlying the development of lateralization.

A COMPARISON OF THE PERFORMANCE AND SOME PHYSIOLOGICAL STRESS OF LAYING HENS KEPT IN BATTERY CAGES AND ON FLOOR PENS SYSTEM

One hundred and eighty hens 18 weeks old were randomly chosen from a flock reared in deep litter system (from one day old) and used in this experiment. Hens were individual weighted and randomly divided into two equal groups (90 hens each). First group, hens were transferred from floor pens to conventional cages system at 18 weeks of age using 30 cages with 3 birds per cage, each cage considered as a replicate. Second group was still in floor pens with 6 hens per square meter, divided to 3 replicates, each replicate 30 hens, to evaluate the effects of transference hens from floor pens (F.) to conventional cages system (Con.) at 18 weeks of age, compared to others which still in floor pens during the first season of egg production (from 20-52 weeks of age) on productive performance and some physiological stress parameters of laying hens. The main results were as follows: After hens were transferred from floor pens to conventional cages at 18 weeks of age, hens which were still in floor pens had significantly heavier body weight at 20 and 24 weeks of age. Also, feed conversion ratio, egg production percentage and egg weight at 24 weeks of age were significantly (P < 0.05) better. Although, feed consumption was insignificantly higher in conventional cages compared to floor pens system. In general, there was no significant effect between two systems on all parameters that were measured in table (1) from week 28 until week 52. There were significantly (P < 0.05) increased in plasma Heterophil/Lymphocyte (H/L) ratio, serum corticosterone and glucose at 20, 24 and 28 weeks of age for hens which transferred to conventional cages at 18 weeks of age compared to others still on floor pens system. Furthermore, the results of egg albumen and yolk corticosterone concentrations were in same trend of previous results where the concentrations of corticosterone in egg albumen and yolk were significantly (P < 0.05) higher in the hens housed in conventional cages at week 24, 28 and 32 of the age compared to the hens housed on floor pens. Moreover, there were no significant effects of the two housing systems at all parameters that were measured in table (2) from the week 36 until the end of the experiment. From the previous results it could be concluded that hens which transferred from floor pens to conventional cages system at 18 weeks of age were stressed at the start of lay, but adapt to their new environment when hens grew older towards the end of the laying period. Finally, it could be recommended to transfer hens from floor pens to conventional cages system to spend eggs laying period in this system (conventional cages system) which consider much better hygienic standards environment than floor pens system.

Welfare indicators in laying hens in relation to nest exclusion

Consumer concerns about the welfare of laying hens are increasing, leading to increased interest in identifying reliable ways to assess welfare. The present study evaluated invasive and non-invasive welfare indicators in relation to a stressful challenge. The study included 126 Lohmann Selected Leghorn hens housed in furnished cages. Welfare indicators were measured between 61 and 70 wk of age in birds excluded from their nests for 5 consecutive d and control birds that had continuous access to nests. Baseline recordings were carried out in both groups prior to and post exclusion period. The assessed indicators were: corticosterone metabolites in droppings (FCM), corticosterone concentration in yolk, corticosterone concentration in plasma, irregularities of eggshells, heterophil to lymphocyte (H:L) ratio, tonic immobility duration, and feather cover. Behavioral observations showed that the birds had a clear preference for using the secluded nest sites, confirming that they were likely to perceive nest exclusion as an undesirable experience. Further, elevated levels of FCM in droppings, yolk corticosterone concentrations, H:L ratios and irregular eggshells were detected in both nest deprived and control birds during the exclusion. This suggests that these indicators were able to detect an increased stress response arising from nest deprivation, and it is hypothesized that the stress spread to birds in adjacent cages with access to nests. There was a positive and consistent correlation between FCM in droppings and eggshell irregularities, also supporting the use of eggshell irregularities as a potential non-invasive welfare indicator. However, the pattern of the stress response varied between indicators and correlations were generally few and inconsistent, highlighting the complexity of the relationship among welfare indicators.

Maternal corticosterone deposition in avian yolk: Influence of laying order and group size in a joint-nesting, cooperatively breeding species

Glucocorticoid hormones play a key role in day-to-day adjustments to fluctuating metabolic needs. These hormones also mediate physiological and behavioral responses to stressful events, allowing individuals to cope with stressors. Various environmental insults, such as a food shortages, predation attempts, and agonistic encounters often elevate plasma glucocorticoid levels in vertebrates. Because exposure to maternally-derived (via circulation or egg) glucocorticoids may be detrimental to the developing embryo, maternal stress can have negative carryover effects on offspring fitness. We examined corticosterone, the primary avian glucocorticoid, concentrations in egg yolk in a plural-breeding, joint-nesting species, the smooth-billed ani (Crotophaga ani), in which females compete among themselves to lay eggs in the final incubated clutch. We investigated whether yolk corticosterone levels varied with laying order and group size. Because egg-laying competition leads to physiological and social stress that is intensified with group size and laying order, we predicted that yolk corticosterone levels should increase from the early to the late egg-laying period and from single female to multi-female groups. In this two-year field study, we found that yolk corticosterone levels of late-laid eggs within the communal clutch were higher in multi-female groups than in single female groups. Results from this study suggest that laying females experience higher levels of stress in multi-female groups and that this maternal stress influences yolk corticosterone concentrations. This study identifies a novel cost of group-living in plural-breeding cooperatively breeding birds, namely an increase in yolk corticosterone levels with group size that may result in detrimental effects on offspring development.

Influence of the rearing system on yolk corticosterone concentration in captive Greater Rheas (Rhea americana).

Many environmental conditions elevate plasma corticosterone in laying birds, leading to elevated hormone accumulation in the egg. We investigated whether maternal yolk corticosterone levels in Greater Rheas differ between fresh eggs collected from an intensive (IRS) and a semi-extensive (SRS) rearing system. After HPLC validation, yolk corticosterone was measured using a corticosterone (125) I radio-immunoassay kit. Results (mean ± SE) showed that eggs collected from the IRS exhibited a significantly higher corticosterone concentration than eggs from SRS (89.88 ± 8.93 vs. 45.41 ± 5.48 ng/g yolk, respectively). Our findings suggest that rearing conditions under an intensive scheme (e.g., small pens with bare ground, no direct foraging and handling) might be perceived as more stressful for Greater Rhea females than semi-extensive rearing conditions (e.g., low animal density distributed in extensive areas and direct foraging), which would result in the transfer of higher yolk corticosterone levels. A better understanding of environmental conditions and female traits that affect yolk corticosterone deposition provides a background for future studies concerning the roles of maternal corticosterone on offspring development. Zoo Biol. 35:246-250, 2016. © 2016 Wiley Periodicals, Inc.

Pair disruption in female zebra finches: consequences for offspring phenotype and sensitivity to a social stressor

Maternal effects can result in transgenerational phenotypic plasticity, in which environmental variation experienced by mothers is translated into phenotypic variation in offspring. Although maternal effects have been a focus of much recent research, little is known about the long-term consequences of disturbance of the maternal social environment on offspring phenotype in socially monogamous and biparental species. We hypothesized that pair separation followed by re-pairing may generate maternal effects on offspring development. Here, we gave previously paired female zebra finches access to new males 6 days following removal of their original partner to assess experimentally the effects of re-pairing (an ecologically relevant form of social disturbance) on female reproductive investment, yolk corticosterone concentrations and subsequent offspring phenotype. Pair disruption boosted growth in female offspring and delayed the development of plumage colour sex dimorphism in males. Although yolk corticosterone concentrations were not affected by the treatment, offspring from treated mothers were less responsive to social isolation in a novel environment compared to control offspring. This is, to our knowledge, the first study demonstrating that maternal re-pairing prior to hatching has long-lasting effects on offspring phenotype in a socially monogamous and biparental species. Our results also suggest that prehatching maternal effects of this social disturbance are not mediated by maternal yolk corticosterone. Additional studies are required to determine the potential pathways of these maternal effects (e.g. other hormones, epigenetic programming, protein/nutrient content of eggs, etc.) and their adaptive value.

Corticosterone in ovo modifies aggressive behaviors and reproductive performances through alterations of the hypothalamic-pituitary-gonadal axis in the chicken

Exposure to excess glucocorticoids during embryonic development affects offspring reproduction and suppresses the hypothalamic-pituitary-gonadal (HPG) axis in mammals. However, whether corticosterone (CORT) causes similar effects in the chicken remains unclear. In the present study, we injected low (0.2μg) and high (1μg) doses of CORT in ovo before incubation and detected changes in aggressive behavior, tonic immobility (TI), reproductive performances, and HPG axis gene expression in posthatch chickens of different ages. High dose of CORT suppressed growth rate from 3 weeks of age, increased the frequency of aggressive behaviors, which was associated with elevated plasma CORT concentration. High-dose CORT significantly (P<0.05) down-regulated arginine vasotocin (AVT), corticotropin-releasing hormone (CRH), 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) and gonadotropin-releasing hormone 1 (GnRH1), while significantly (P<0.05) up-regulated gonadotropin-inhibitory hormone (GnIH) and 11β-HSD1 mRNA expression in the hypothalamus. Glucocorticoid receptor (GR) and 20-hydroxysteroid dehydrogenase (20-HSD) mRNA levels were not affected by CORT treatment. High-dose CORT significantly (P<0.05) reduced egg production and egg quality, which was associated with decreased ovary and oviduct weight. Moreover, CORT exposure significantly decreased (P<0.05) luteinizing hormone (LH) receptor and follicle-stimulating hormone (FSH) receptor mRNA abundance in theca cells of ovarian follicles 1 (F1), F2 and F3. In addition, yolk CORT concentration was significantly higher in eggs laid by hens prenatally exposed to high-dose CORT. Our findings suggest that in ovo administration of CORT programs the aggressive behaviors and reproductive functions in the chicken through alterations of HPG axis.

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.

Genetic variations alter production and behavioral responses following heat stress in 2 strains of laying hens

Genetic differences alter the type and degree of hens’ responses and their ability to adapt to a stressor. This study examined the effects of genotypic variations on the productivity and behavior of laying hens following heat stress (HS). Two strains of White Leghorn hens were used: DXL (Dekalb XL), a commercial strain individually selected for egg production and KGB (kind, gentle bird), a strain selected for high group productivity and survivability. Ninety hens (48 DXL and 42 KGB) at 28 wk of age were randomly assigned to either a hot (H: mean = 32.6°C) or control (C: mean = 24.3°C) treatment and housed in pairs by strain for 9 d. Egg production and quality, behavior, body and organ weights, and circulating hormone concentrations were measured. Heat-stressed hens had lower egg production [adjusted (adj) P < 0.001] than their respective controls. Among H-DXL hens, egg weight tended to be reduced at d 1 and was reduced at d 9 (adj P = 0.007), but was reduced only at d 9 among H-KGB hens (adj P = 0.007). Eggshell thickness was also reduced among H hens at d 9 (adj P = 0.007), especially among H-KGB hens (adj P = 0.01). Plasma triiodothyronine concentration was reduced among H-hens (adj P = 0.01), especially among H-DXL hens (adj P = 0.01). Neither temperature nor strain affected the plasma thyroxine and plasma and yolk corticosterone concentrations. Heat-stressed hens spent less time walking (adj P = 0.001) and more time drinking (adj P = 0.007) and resting (adj P = 0.001) than C-hens. The results indicate that although HS reduced production and caused behavioral changes among hens from both strains, the responses differed by genotype. The data provide evidence that genetic selection is a useful strategy for reducing HS response in laying hens. The results provide insights for conducting future studies to develop heat-resistant strains to improve hen well-being, especially under the current commercial conditions.

Effect of maternal corticosterone on utilisation of residual yolk sac fatty acids by developing broiler embryo

1. Increased concentrations of maternal corticosterone are deposited into egg yolk under stress conditions. This experiment investigated the effect of maternal corticosterone on yolk and yolk sac fatty acid profiles of eggs and developing broiler embryos. 2. At 42 weeks of age, 200 broiler breeder females were randomly divided into two groups: maternal corticosterone (MC): 2 mg/hen/d of corticosterone dissolved in 1 mL of 99% ethanol and mixed in the individual daily feed for a 14 d period, and control: 1 mL of ethanol added to the individual daily feed. Hens were inseminated, and eggs were collected daily from d 3 of corticosterone feeding to d 14 and incubated. Fatty acid profiles of egg yolk and yolk sac were analysed before incubation and at 12, 14, 18 and 21 d of incubation. 3. Yolk corticosterone concentrations were greater in MC eggs. Before incubation, eggs from MC had lower DHA (22 : 6 n-3) but higher stearic (18 : 0) and dihomo-gamma linolenic (20 : 3 n-6 Cis 8,11,14) acid content compared with the control. 4. Higher concentrations of stearic (18 : 0), elaidic (18 : 1 tr n-9), eicosenoic (20 : 1 n-9), eicosadienoic (20 : 2 n-6), dihomo-gamma linoleic (20 : 3 n-6) and arachidonic (20 : 4 n-6) acids and lower concentrations of myristic (14 : 0), palmitoleic (16 : 1 n-7), linoleic (18 : 2 n-6) and DHA (22 : 6 n-3) were found at different periods of incubation in the residual yolk sac of MC than from controls. 5. The results suggest that the preferentially selective absorption of fatty acids is related to specific tissue requirements.

Yolk and albumen corticosterone concentrations in eggs laid by white versus brown caged laying hens

Maternal stress in birds can have permanent transgenerational effects through the transmission of stress hormones to offspring via the egg yolk. Previous studies have shown that White Leghorn hens show a heightened response to stress compared with Hy-Line Brown hens, producing significantly more corticosterone and displaying longer bouts of tonic immobility after handling, whereas baseline levels of corticosterone are similar between the strains. We tested the hypothesis that higher stress responsiveness would correspond to chronic accumulation and thus higher concentrations of corticosterone in egg yolks after exposure to stressors associated with routine maintenance. Eggs were collected from white and brown hens that were undisturbed except for daily feeding and routine egg collections. Corticosterone was quantified in plasma, egg yolks, and albumen and compared between strains. We predicted that corticosterone concentrations in yolk would be higher in eggs from white versus brown hens but that albumen corticosterone would not differ between strains due to the short term of albumen deposition. As predicted, yolk corticosterone concentrations were significantly higher in eggs produced by white hens, approximately twice those found in eggs laid by brown hens. Plasma and albumen concentrations of corticosterone were similar between groups. These results suggest that offspring hatching from eggs laid by White Leghorn hens are exposed to significantly more corticosterone through concentration in the egg yolk, which could permanently imprint offspring physiology and behavior.

Egg size and yolk steroids vary across the laying order in cockatiel clutches: A strategy for reinforcing brood hierarchies?

When a female bird begins incubation before clutch completion, the nestlings hatch sequentially, and a size hierarchy forms within the brood. This size hierarchy may be minimized or exacerbated through differential allocation of resources to eggs across the laying order. In this study, we characterize intra-clutch variation in cockatiel clutches by measuring egg mass, yolk mass, and concentrations of yolk testosterone, androstenedione, and corticosterone. Cockatiels are a long-lived member of the Psittaciformes. Because asynchronous hatching may reduce sibling competition and allow for extended development periods in long-lived birds, we predicted that female cockatiels would allocate maternal resources in a way that would reinforce the brood size hierarchy. Significant within-clutch differences in egg size and steroid concentrations were observed. Eggs at the end of the laying sequence were smaller and had significantly smaller yolks than eggs early in the laying order. Fifth-laid eggs, as well as first-laid eggs, contained significantly lower concentrations of testosterone than eggs in other positions of the laying sequence. No differences in yolk androstenedione concentration were observed. Yolk corticosterone concentrations increased linearly with laying order. Together, these patterns might reinforce the brood size hierarchy created by asynchronous hatching.

Comparisons among serum, egg albumin and yolk concentrations of corticosterone as biomarkers of basal and stimulated adrenocortical activity of laying hens

1. Serial blood samples from individual birds were analysed for corticosterone concentrations under basal and stimulated conditions, and matched to eggs from the same birds for comparison to albumin and yolk concentrations of corticosterone. 2. Serum corticosterone exhibited increases in response to stimulation by ACTH and Handling stress. There were no significant increases in egg albumin or yolk concentrations of corticosterone following stimulation. 3. Several significant correlations were observed between the mean and area under the curve (AUC) measurements of serum corticosterone concentrations with albumin and yolk corticosterone concentrations in eggs laid from 1 to 2 d later. 4. The results demonstrated a relationship between endogenous concentrations of serum corticosterone that reflected daily adrenocortical output with albumin and yolk corticosterone concentrations in eggs laid the following day. 5. The results do not support the concept of albumin and yolk concentrations of corticosterone as biomarkers of acute adrenocortical responses to stimulation.

Invasive and noninvasive measurement of stress in laying hens kept in conventional cages and in floor pens

Measurements of the heterophil:lymphocyte (H/L) ratio (invasive technique) and corticosterone in yolk and albumen (noninvasive techniques) were used to measure stress in 3 commercial laying strains, Lohmann White (LW), H&N White (HN), Lohmann Brown (LB), and a noncommercial cross (CR) between Rhode Island Red (male) and Barred Plymouth Rock (female), kept in conventional cages or floor pens. All chicks were reared in their respective environments, and 450 and 432 pullets were placed at 18 and 7 wk of age in cages and floor pens, respectively. Blood from 12 hens per strain was taken at 19, 35, and 45 wk of age in each housing system. A total of 100 heterophils and lymphocytes were counted and their ratio (H/L ratio) was calculated. Corticosterone was measured in yolk and albumen from 12 hens per strain in each housing system at 22 and 45 wk of age. The H/L ratio was within the normal range. The interaction between environment and strain for the H/L ratio showed that in both environments, LB and CR hens had a higher H/L ratio than LW and HN layers. In cages, there were significant differences in H/L ratios between LW and HN hens that were likely due to genetic differences. The LW hens had significantly lower corticosterone concentrations in yolk than LB hens. In cages but not floor pens, yolk corticosterone concentrations at wk 22 were significantly higher than at wk 45. In floor pens but not cages, albumen corticosterone at wk 22 was higher than at wk 45. The H/L ratios suggest that none of the hens were unduly stressed, and corticosterone levels in yolk and albumen support the suggestion that hens adapted to their environments with age. Although measurement of yolk corticosterone and the H/L ratio may be comparable, the measurement of corticosterone level in the albumen may differ because it is secreted over a short time.

Egg Corticosterone: A Noninvasive Measure of Stress in Egg-laying Birds

Quantitative measures of corticosteroids in biological samples that can be obtained noninvasively, such as saliva, feces, and body hair, have important potential as contributing elements in assessing the quality of captive environments and the severity of experimental procedures. Egg-laying chickens may be of particular interest because the corticosterone contents of the egg may have potential as a convenient measure of preceding adrenocortical activity. To develop methods to reliably quantify corticosterone content in the egg white and yolk, corticosterone content in eggs from 15 egg-laying chickens housed in single production cages were compared with that of eggs from 15 sister chickens, group housed in 1450 cm2 cages equipped with bedding, straw nests, sand baths, and perches. Approximately 80% of the total amount of corticosterone in the eggs was found in the yolk, and there was a positive correlation between yolk corticosterone concentration and total egg corticosterone (r = 0.90, n = 30, P < .001). The egg white contained approximately 20% of the total amount of corticosterone, but there was no correlation between concentrations in the white and the total corticosterone content of the eggs (r = 0.003). There was no difference in the white and yolk corticosterone concentrations or total egg corticosterone between singly housed and group-housed egg-laying hens. Quantitative analyses of corticosterone concentration in eggs may assist when analyzing the stressfulness of experimental procedures and major changes to the birds' environment that affect the activity of the hypothalamus-pituitary-adrenal axis.

Sex differences in the organizational effects of corticosterone in the egg yolk of quail

Previously, we found that experimentally elevated plasma corticosterone was transferred to egg yolk by female Japanese quail ( Coturnix coturnix japonica), and that the chicks hatched from these eggs grew more slowly than controls and had higher responsiveness of the hypothalamic–pituitary–adrenal (HPA) axis as adults. Here, we tested whether exposure to high yolk corticosterone was responsible for the slowed growth and elevated HPA responsiveness by manipulating the steroid content of eggs directly. Eggs were injected prior to incubation with a dose of corticosterone calculated to increase total yolk corticosterone concentration by two standard deviations. We found that elevated yolk corticosterone slowed growth in male but not female chicks and decreased the HPA responsiveness of female but not male adults, in contrast to the results of elevated corticosterone in laying females. Our results are consistent with others that demonstrate sex differences in the organizational effects of glucocorticoids. The mechanisms and adaptive value of such differences have yet to be determined.