T-maze behavior and early egg production in Japanese quail selected for contrasting adrenocortical responsiveness

Mechanisms underlying reproductive responses of Japanese quails to heat stress conditions

Exposure to heat stress can cause a significant increase in the death rate and disease susceptibility of poultry birds, ultimately impacting the profitability of the poultry industry. Despite being a more economical choice, Japanese quails (Coturnix japonica) are not immune to the harmful effects of heat stress. Quails may experience negative effects on their reproductive performance due to excessive reactive molecules caused by heat stress. However, they have developed various mechanisms to maintain their reproductive abilities in such conditions. The neuroendocrine system in birds plays a vital role in regulating their reproductive responses to thermal stress, and it is also connected to other environmental factors such as photoperiod that can impact their reproductive performance. Hormones are crucial in the complex interactions necessary for sexual maturation and reproductive responses to heat stress in Japanese quails living in stressful thermal conditions.

Environmental Enrichment as Part of the Improvement of the Welfare of Japanese Quails

Simple Summary

Nowadays, keeping animals in cage systems is controversial. Regulations and increased consumer awareness are causing cage systems to lose ground in many countries. In the case of Japanese quails bred for both egg and meat production, their maintenance in a non-cage system is very difficult and uneconomical; therefore, they are kept in cages, and, unlike egg-laying hens, the regulations only regulate the basic parameters, such as cage size and access to food and water. Taking this into account, studies have been conducted that indicate that keeping quails in enriched cages improves the birds’ welfare.

Abstract

The aim of this study was to evaluate the indicators of the behavioural and physiological welfare of Japanese quails (Coturnix japonica) as possible responses to the enrichment of the birds’ habitat. The study sample consisted of 280 Japanese quails (224 ♀ and 56 ♂, respectively). Birds of 5 weeks of age were randomly divided into seven equally sized groups and then divided into replication subgroups (four per group, 10 birds in each replication). Birds were maintained in 0.5 m² cages with unrestricted access to water and food. The experimental factor was the presence or absence of enrichment of the birds’ cages: the nest box, scratcher, plastic corrugated pipe (tunnel), limestone cubes, sandbathing box and feeder box with a drilled cover. Quails were subjected to behavioural tests (tonic immobility and open field tests) and, after 6 weeks, blood samples were taken from them to determine their biochemical indices as well as their cortisol and corticosterone levels. An additional element was the assessment of fertility indices. The presence of enrichment was shown to reduce behavioural disturbances in Japanese quails. This study also found that the colour and shape of an object were very important regarding the birds’ interest in it. Additionally, individuals kept in enriched cages, who were allowed to exhibit their natural behavioural patterns, had lower stress levels.

Impact of male-female cohabitation period on behavioral aspects, fertility, hatchability, and hormonal estimates of Japanese quail

To evaluate the impact of male-female cohabitation period on the fertility, hatchability, injuries response, and some hormonal estimates in Japanese quails. A total of 288 mature Japanese quails were equally divided into 3 groups (3 groups × 8 replicates × 12 birds), with 1 Male: 2 Females sex ratio. In the first group (control), male and female quails were reared continuously together, while the males in the second and third groups were reared together with females once or twice/wk times (24 h/ time), respectively throughout the experiment. The obtained results showed that final body weight (FBW/g), fertility (%), and hatchability (%) in the second and third groups significantly (P ≤ 0.01) increased compared with the control group. Laying quails in the second and third groups significantly (P ≤ 0.01) produced more and heavier eggs, while the feed consumption and feed conversion ratio were significantly (P ≤ 0.01) decreased compared with the control group. The injuries response for both sex in the second and third groups significantly (P ≤ 0.01) decreased compared with the control group. The cloacal size (mm²) for quails in the third group significantly (P ≤ 0.01) increased than those of the first and second groups, while the testes (%) were not affected. The testosterone hormone concentration for male chickens in the second and third groups significantly (P < 0.01) decreased, while the female progesterone hormone concentration (ng/mL) significantly (P < 0.01) increased compared with the control group. The means of red blood cells (RBC/106), white blood cells (WBC/103), and hemoglobin (g/dL) for quails in the second and third groups significantly (P < 0.01) increased, while heterophil/lymphocyte (H/L ratio) significantly (P < 0.01) decreased compared with the control group. Thus, it could be concluded that the reduction male-female cohabitation period of quails is recommended for improving the fertility and hatchability percentages as well as and some hormonal estimates.

Immediate and transgenerational effects of thymol supplementation, inactivated Salmonella and chronic heat stress on representative immune variables of Japanese quail

Environmental challenges are integrated in the inmunoneuroendocrine interplay, impacting the immune system of the challenged individuals, and potentially implying transgenerational effects on their offspring. This study addressed whether dietary supplementation with thymol can modulate the immune response of adult Japanese quail when simultaneously exposed to an inoculum of inactivated Salmonella Enteritidis and a chronic heat stress (CHS). We also evaluated whether the experienced situations by adults can affect the immune response of their undisturbed offspring. In the parental generation, supplemented quail exposed to CHS had a higher inflammatory response and similar values of the heterophil/lymphocyte (H/L) ratio than those that were not supplemented. In their offspring, those chicks whose parents were exposed to CHS showed higher inflammatory response and lower antibody production. Regarding the H/L ratio, chicks whose parents were supplemented showed lower H/L ratio values. Dietary supplementation with thymol partially and positively modulated the inflammatory response and avoided H/L ratio alteration in the parental generation exposed to high environmental temperatures, suggesting these adults were better at dealing with the challenge. The lower H/L ratio values in the offspring suggests that chicks are more capable to deal with potential stressful situations associated with conventional breeding conditions.

Genetic correlations between behavioural responses and performance traits in laying hens

OBJECTIVE

The aim of the study was to evaluate genetic correlations between the behavioural profile and performance in laying hens as an indirect answer to the question whether the observed behavioural responses are associated with increased levels of stress in these birds.

METHODS

The assessment of birds' temperament was carried out using the novel objects test. The behavioural test was conducted in two successive generations comprising 9,483 Rhode Island White (RIW) birds (approx. 4,700 individuals per generation) and 4,326 Rhode Island Red (RIR) birds (approx. 2,100 individuals per generation). Based on the recorded responses, the birds were divided into two groups: a fearful profile (1,418 RIW hens and 580 RIR hens) and a brave/curious profile (8,065 RIW hens and 3,746 RIR hens). The birds were subjected to standard assessment of their performance traits, including SM, age at sexual maturity; ST, shell thickness; SG, egg specific gravity; EW, mean egg weight; IP, initial egg production; and HC, number of hatched chicks. The pedigree was three generations deep (including two behaviour-recorded generations). Estimation of the (co)variance components was performed with the Gibbs sampling method, which accounts for the discrete character of the behavioural profile denotation.

RESULTS

The analyses revealed negative correlations between the performance traits of the laying hens and the behavioural profile defined as fearful. In the group of fearful RIW birds, delayed sexual maturation (0.22) as well as a decrease in the initial egg production (-0.30), egg weight (-0.54), egg specific gravity (-0.331), shell thickness (-0.11), and the number of hatched chicks (-0.24) could be expected. These correlations were less pronounced in the RIR breed, in which the fearful birds exhibited a decline in hatchability (-0.37), egg specific gravity (-0.11), and the number of hatched chicks (-0.18). There were no correlations in the case of the other traits or they were positive but exhibited a substantial standard error, as for the egg weight.

CONCLUSION

To sum up the results obtained, it can be noted that behavioural responses indicating fearfulness, i.e. escape, avoidance, and approach-avoidance may reflect negative emotions experienced by birds. The negative correlations with performance in the group of fearful hens may indirectly indicate a high level of stress in these birds, especially in the white-feathered birds, where stronger performance-fearfulness correlations were found. Fearful birds should be eliminated from breeding by inclusion of the behavioural profile in the selection criterion in the case of laying hens.

Evidence of phenotypic and genetic relationships between sociality, emotional reactivity and production traits in Japanese quail

The social behavior of animals, which is partially controlled by genetics, is one of the factors involved in their adaptation to large breeding groups. To understand better the relationships between different social behaviors, fear behaviors and production traits, we analyzed the phenotypic and genetic correlations of these traits in Japanese quail by a second generation crossing of two lines divergently selected for their social reinstatement behavior. Analyses of results for 900 individuals showed that the phenotypic correlations between behavioral traits were low with the exception of significant correlations between sexual behavior and aggressive pecks both at phenotypic (0.51) and genetic (0.90) levels. Significant positive genetic correlations were observed between emotional reactivity toward a novel object and sexual (0.89) or aggressive (0.63) behaviors. The other genetic correlations were observed mainly between behavioral and production traits. Thus, the level of emotional reactivity, estimated by the duration of tonic immobility, was positively correlated with weight at 17 and 65 days of age (0.76 and 0.79, respectively) and with delayed egg laying onset (0.74). In contrast, a higher level of social reinstatement behavior was associated with an earlier egg laying onset (-0.71). In addition, a strong sexual motivation was correlated with an earlier laying onset (-0.68) and a higher number of eggs laid (0.82). A low level of emotional reactivity toward a novel object and also a higher aggressive behavior were genetically correlated with a higher number of eggs laid (0.61 and 0.58, respectively). These results bring new insights into the complex determinism of social and emotional reactivity behaviors in birds and their relationships with production traits. Furthermore, they highlight the need to combine animal welfare and production traits in selection programs by taking into account traits of sociability and emotional reactivity.

Steroid hormones, stress and the adolescent brain: a comparative perspective

Steroid hormones, including those produced by the gonads and the adrenal glands, are known to influence brain development during sensitive periods of life. Until recently, most brain organisation was assumed to take place during early stages of development, with relatively little neurogenesis or brain re-organisation during later stages. However, an increasing body of research has shown that the developing brain is also sensitive to steroid hormone exposure during adolescence (broadly defined as the period from nutritional independence to sexual maturity). In this review, we examine how steroid hormones that are produced by the gonads and adrenal glands vary across the lifespan in a range of mammalian and bird species, and we summarise the evidence that steroid hormone exposure influences behavioural and brain development during early stages of life and during adolescence in these two taxonomic groups. Taking a cross-species, comparative perspective reveals that the effects of early exposure to steroid hormones depend upon the stage of development at birth or hatching, as measured along the altricial-precocial dimension. We then review the evidence that exposure to stress during adolescence impacts upon the developing neuroendocrine systems, the brain and behaviour. Current research suggests that the effects of adolescent stress vary depending upon the sex of the individual and type of stressor, and the effects of stress could involve several neural systems, including the serotonergic and dopaminergic systems. Experience of stressors during adolescence could also influence brain development via the close interactions between the stress hormone and gonadal hormone axes. While sensitivity of the brain to steroid hormones during early life and adolescence potentially leaves the developing organism vulnerable to external adversities, developmental plasticity also provides an opportunity for the developing organism to respond to current circumstances and for behavioural responses to influence the future life history of the individual.

Chronic stress and environmental enrichment as opposite factors affecting the immune response in Japanese quail (Coturnix coturnix japonica)

Procedures in the commercial production of animals involve stressful situations which lessen the animal's welfare. This study on Japanese quail evaluated whether an environmental enrichment manipulation can affect avian immune responses and if combined with a chronic stressor exposure can help to counteract the negative effects of stress on the immune system. Potential gender effects were also considered. After hatch, half of the birds were housed in non-enriched boxes and half were housed in environmentally enriched boxes. From day 33 to 42 of age, all birds within half of the non-enriched and enriched boxes remained undisturbed while the other half were daily exposed to a 15 min restraint stressor (chronic stressor). The inflammatory response (lymphoproliferation after phytohemagglutinin-p), percentage of lymphocytes, heterophil/lymphocyte (H/L) ratio and primary antibody response against sheep red blood cells were assessed. The chronic stressor application and the enrichment procedure, respectively, either increased or reduced the four immunological parameters evaluated and always in opposite directions. Males consistently showed lower antibody titres than females and presented the highest H/L ratio in response to the stressor when reared in the non-enriched environment. The findings indicate that submitting these animals to an enriched environment can be effectively used to improve their immune response and to reduce the detrimental effects of a stressor exposure.

Short-term spatial memory responses in aged Japanese quail selected for divergent adrenocortical stress responsiveness

Stress-induced glucocorticoids can dampen learning and spatial memory via neuronal damage to the hippocampus. Cognition losses can be transient (associated with acute stress episodes) or permanent as in aged individuals who show chronic glucocorticoid-induced accelerated brain aging and neurodegeneration (dementia). Thus, chronic versus acute stress effects on spatial memory responses of quail selected for reduced (low stress, LS) or exaggerated (high stress, HS) plasma corticosterone (B) response to brief restraint were assessed. Aged food-motivated male LS and HS quail were tested for 10 min in a feed-baited 8-arm radial arm maze (RAM) 1) at 255 d of age (quail who had experienced lifelong management stressors but who were otherwise never intentionally stressed; that is, chronically stressed birds), 2) on the next day post-acute stressor treatment (5 min of restraint), and 3) on the next day without treatment (acute stress recovery). The RAM tests used the win-shift procedure in which visited arms were not rebaited. Radial arm maze performance was measured by determination of the total number of arm choices made, the number of correct entries made into baited arms out of the first 8 choices, the time required to make a choice, and the number of pellets eaten. Line effects (P < 0.001 in all cases) were detected for total number of arm choices made (HS < LS), number of correct entries made into baited arms out of the first 8 choices (HS < LS), time required to make a choice (HS > LS), and number of pellets eaten (HS < LS). However, neither the effects of day of RAM testing nor its interaction with line further influenced these variables. Thus, although selection for divergent plasma B responsiveness to an acute stressor was found to be associated with severe impairment of spatial memory in aged male HS compared with LS quail, the observed spatial memory impairments (HS > LS) could not be further altered by acute stressor treatment. Line differences in cognition may reflect lifelong management-induced stress episodes that periodically produce higher plasma B responses in HS than LS quail, which underlie HS quail memory deficits, or other etiologies, or both.

Fear responses of offspring from divergent quail stress response line hens treated with corticosterone during egg formation

Increased fearfulness has been associated with adrenocortical activation. Maternal corticosterone (B) treatment increases egg B, and elevated B in ovo enhances chick avoidance of humans. Quail selected for exaggerated (high stress, HS) rather than reduced (low stress, LS) plasma B response to stress are more fearful, and more B is found in HS hen eggs. Thus, we used tonic immobility (TI) and hole-in-the-wall box (HWB) emergence tests to assess fear in chicks hatched from eggs of LS and HS hens implanted with B or no B (CON). The number of inductions required to attain TI, latency to first alert head movement, and duration of TI were determined in one study and the latency until first vocalization (LATVOC), numbers of vocalizations (VOCS), proportions of chicks vocalizing, and the latencies to head (HE) and full-body (FE) emergence from a HWB were assessed in another. The LS chicks required less inductions (P < 0.0005) and had shorter latency to first alert head movement (P < 0.02) than HS chicks, although the duration of TI was unaffected by any of the treatments. During the acclimation period of the HWB tests, more (proportions of chicks vocalizing; P < 0.0001) HS chicks alarm-called sooner (LATVOC; P < 0.0001) and more often (VOCS; P < 0.0001) than did LS chicks, and, although maternal implant treatment did not affect LATVOC, progeny of B-implanted hens showed a tendency toward less (P < 0.07) VOCS than the CON. Chicks hatched from eggs of B-implant mothers also took longer to achieve HE (P < 0.06) and FE (P < 0.05) from the HWB than did their CON counterparts. Stress line, implantation treatment, and their interaction did not alter HE or FE responses. The data suggest that quail stress line genome may or may not be affecting certain fear and alarm responses in chicks via the same mechanism(s) that underlies how elevating maternal B increases egg levels of B that in turn alters the fear behavior of progeny.

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

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

Ontogeny of the Cloacal Gland in Male Japanese Quail Classified in a T-Maze

Broiler chicks that traverse a T-maze quickly to reinstate contact with their companions (HP, high performers) are known to grow faster, are more social, and have a reduced plasma corticosterone response to acute stress than slower chicks (LP, low performers). High-performing quail from a line selected for reduced rather than exaggerated (high-stress) adrenocortical stress responsiveness also show enhanced female reproductive performance when compared with LP-high-stress quail. Herein, time courses of male sexual development were evaluated in genetically unremarkable quail that were categorized at 2 d of age as HP or LP in the T-maze. Body weight, cloacal gland volume (CVOL), proportion of individuals that produced cloacal gland foam, intensity of foam production, and CVOL relative to BW (RCVOL) were determined weekly from 4 to 10 wk of age, and again at 22 wk, along with absolute and BW-adjusted testes weight. Although CVOL and RCVOL were initially similar in both T-maze groups, both variables were greater (P < 0.05) in HP than in LP quail between 6 and 10 wk of age. High-performing birds also showed a trend (P < 0.1) of greater cloacal gland foam than their LP counterparts from 5 to 7 wk. From 8 wk on, all birds were in foam production. Intensity of foam production results generally mimicked those found for CVOL and RCVOL. Body weights were higher (P < 0.05) in HP than LP quail from 5 to 7 wk. No T-maze group differences were found in any of the variables at 22 wk of age. The results suggest that rapid negotiation of the T-maze is associated with accelerated growth and puberty in male quail, although the enhanced reproductive development of HP males does not remain extant in aged adults.

Cloacal Gland Growth Differences in High and Low Plasma Corticosterone Stress Response Line Male Quail Reared Under Short Daylengths

Mail quail selected (generation 32) for reduced [low stress (LS)] or exaggerated [high stress (HS)] plasma corticosterone stress response to brief mechanical restraint (5 min of immobilization) were studied for differences in the growth of their cloacal glands when reared essentially lifelong on short day lengths of 8L:16D. Post-brooding, at 4 wk of age, 96 quail (48 LS+48 HS) were housed in cages (1 LS and 1 HS male/cage), and the short day light treatment was instigated. Using a digital caliper, cloacal gland (CG) size measurements (length and width, mm) were made biweekly beginning at 42 d of age and ending at 196 d of age (28 wk old). The CG volume (CVOL) was calculated from these measurements using a literature-proposed formula. The CVOL in both lines increased similarly with increasing age from 6 to 12 wk of age. However, beginning at 14 wk of age and thereafter, LS males showed greater (P<0.05) CVOL than HS ones. No further increases in CVOL were observed in either line at 24 wk of age beyond that seen at 22 wk. This study demonstrated that although both lines show CG development under short days, eventually CG growth becomes comparatively stymied in the HS males. Furthermore, the maintenance of similarly lower CVOL in HS than LS males, CVOL that showed no further increase from 22 to 24 wk of age, suggests that holding these quail lifelong on short days results in, comparatively, yet another permanent negative reproductive consequence in quail selected for exaggerated plasma corticosterone stress responsiveness.

Stressor-induced changes in open-field behavior of Japanese quail selected for contrasting adrenocortical responsiveness to immobilization

The effect of no treatment (undisturbed controls; CON) or 5 min exposure to immobilization stress (STR) before assessment of open-field behavior in Japanese quail lines selected for high (high stress; HS) or low (low stress; LS) plasma corticosterone (B) response to a similar immobilization stress was examined. During a 5-min test period in an open field, the following behavioral measurements were made: the latency to ambulate (LAMB), the number of open-field floor sectors entered (SECTORS), and freezing behavior (total time spent in complete silence and inactivity, apart from slight movements associated with respiration; FREEZE). A further measure of ambulation across time (ambulation rate; ARATE) was calculated using the formula: ARATE = (SECTORS/[(300 s test ceiling)--LAMB)]. The LS-quail showed higher (P < 0.04) ARATE and lower (P < 0.05) FREEZE behavior than did their HS counterparts. When compared with the CON, quail exposed to STR showed decreased ARATE (P < 0.02) and numbers of open-field SECTORS entered (P < 0.04). More importantly, the LS-CON exhibited a higher (P < 0.05) mean ARATE, less FREEZE behavior, and increased numbers of SECTORS entered than did the other 3 treatment groups (LS-STR, HS-CON, and HS-STR), all of which showed similar responses for these variables. The LS-CON vs. HS-CON findings support our contention that selection for reduced adrenocortical responsiveness has been accompanied by a concomitant decrease in underlying fearfulness (exemplified herein by heightened activity in the open field in LS-CON). We further show here that this relationship was eliminated by application of an acute stressor before open-field testing of LS quail, wherein a reduction in activity similar to that found in both HS quail treatment groups was evident in comparison to the LS-CON.

Early T-maze behavior and broiler growth

In the laboratory and at a commercial farm in Argentina, chicks that showed a short latency to exit a T-maze (LEX) (HP, high performance) gained more weight than those with a longer LEX (LP, low performance). The present study re-examined this relationship and evaluated additional T-maze measures using broilers reared in quasi-intensive, environmentally controlled conditions. In the T-maze, a mirror strategically placed at the end of a corridor stimulates the test chick to leave the isolation chamber (start box) and to move toward its reflection. Having done so, it can then see other birds and thereby be further stimulated to completely exit the maze. However, when a test bird hesitates or stops at the mirror, its performance categorization may be confounded. Herein, the T-maze performance of 3-d-old broiler chicks was assessed using three different measurements: 1) the latency to exit the start box (LEB), 2) the latency to reach the mirror section of the maze (LRM), and 3) LEX. The fastest (top 25%) and slowest (bottom 25%) of the birds within a sex and within each of the three T-maze criteria were classified as HP and LP chicks, respectively. The relationships between these measures and body weight were examined in 4-, 42-, and 56-d-old males and females. Irrespective of the T-maze classification criteria used, HP and LP chicks had similar body weights at 4 d of age. However, chicks classified as HP according to LEB or LRM measures were heavier at 42 and 56 d of age than LP ones (P < 0.02 for all comparisons). These differences were apparent in both sexes. On the other hand, there were no detectable differences in body weight at the latter ages between chicks categorized as HP or LP according to their LEX scores. The present results indicate that 1) broiler chicks that exit the T-maze start box and reach the mirror quickly subsequently grow faster than their slower LP counterparts and 2) LEB and LRM are better predictors of growth than the LEX value used in previous studies.

Genetic characterization of stress responsiveness in Japanese quail. 1. Analyses of line effects and combining abilities by diallel crosses

The inheritance of stress responsiveness (line effects and combining abilities) was phenotypically studied in progeny from diallel crosses of randombred (RB) quail and quail selected for exaggerated (high stress, HS) or reduced (low stress, LS) plasma corticosterone (CS) response to brief immobilization. The three genotypes were crossed in a 3 x 3 factorial arrangement of treatments that allowed all possible crosses between RB, LS, and HS males with RB, LS, and HS females. The nine crosses produced 479 progeny. At 28 d of age, quail of each cross were stressed by immobilization, and blood was sampled. Plasma CS was used to estimate stress responsiveness in the progeny of each cross. Estimates of the following genetic effects were made: average post-immobilization plasma CS response within each cross, general combining ability (GCA), and specific combining ability (SCA). Differences (P < 0.05) in plasma CS response to immobilization between crosses involving the LS and HS lines (HS crosses > LS crosses) were commonly observed. There were no significant differences in the means of plasma CS responses between males and females within each of the crosses except for the marginal (P = 0.07) sex difference (male > female) found within the LL cross (LS male with LS female). The GCA estimates were -1.23, -2.89, and 5.08 for the RB, LS, and HS quail, respectively. The SCA was not significant for any diallel mating except HH (P < 0.007). Line effects on plasma CS response were different from zero for the LS and HS lines.

Genetic characterization of stress responsiveness in Japanese quail. 2. Analyses of maternal effects, additive sex linkage effects, heterosis, and heritability by diallel crosses

Diallel crosses were used to investigate the genetic inheritance of stress responsiveness through examination of population effects in progeny of randombred (RB) quail and quail selected for reduced (low stress, LS) or exaggerated (high stress, HS) plasma corticosterone (CS) response to brief immobilization. The three genotypes were crossed in a 3 x 3 factorial arrangement of treatments that allowed all possible crosses between RB, LS, and HS males with RB, LS, and HS females. The nine crosses produced 479 progeny that were, at 28 d of age, stressed by immobilization, and a sample of blood was collected. The following quantitative genetic parameters were estimated for plasma CS: heritability, heterosis, maternal effects, sex-linkage effects, and heterosis due to the sex chromosomes. Genotypic-phenotypic correlations within RB quail and quail of the two selected lines were also obtained. Maternal effects were different (P < 0.05) from zero for the plasma CS responses of all three genotypes. Additive sex linkage effects on plasma CS responses were variable and of much less importance than maternal effects. The correlations between plasma CS response and genotype were: 0.22 for RB quail and 0.37 and 0.55 for quail of the LS and HS lines, respectively. Heterosis effects were low and most likely due to either an increase in homozygozity of genes on the sex chromosomes or an increase of maternal effects within reciprocal crosses. Heritability, estimated for the post-immobilization plasma CS response, was 0.05 for RB quail and 0.14 and 0.30 for quail of the LS and HS lines, respectively.