Behavioural and adrenocortical responses of domestic chicks to systematic reductions in group size and to sequential disturbance of companions by the experimenter

Domestication and social environment modulate fear responses in young chickens

Domesticated species differ from their wild ancestors in a mosaic of traits. Classical domestication theories agree that reactivity to fear and stress is one of the main traits affected. Domesticated species are expected to be less fear and stress prone to than their wild counterparts. To test this hypothesis, we compared the behavioural responses of White Leghorn (WL) chicks to their wild counterparts, Red Junglefowl (RJF) chicks in risk-taking situations. In order to obtain food, the chicks faced an unknown and potentially harmful object at the presence or absence of a social partner. We found that according to our predictions, RJF were more stressed and fearful of the object than the WL. Still, RJF were more explorative than WL. Additionally, the presence of a social partner reduced the fear response in both, but had a stronger effect on RJF. Finally, WL were more food orientated than the RJF. Our results confirmed classical domestication hypotheses of downregulation of the stress system and importance of the social partner in domesticated farm chicken.

Screening of the Behavioral Tests for Monitoring Agonistic Behavior of Layer Chicks

Chicken agonistic behavior, a type of social behavior related to threatening and fighting, is among the most serious problems in the poultry industry. However, due to luck of effective models for investigating the brain mechanisms of the behavior, no effective measures have been taken. This study, therefore, aimed to select the behavioral tests available for monitoring chicken agonistic behavior. Two behavioral tests, resident-intruder (R-I) test and social interaction (SI) test, were performed for 10 minutes in 10 pairs of male layer chicks at 8, 12, 16, 20, and 24 days of age, and total agonistic frequencies (TAF: Sum of the frequencies of agonistic displays like pecking, biting, kicking, threatening, and leaping) and latency (the period of time from the beginning of the behavioral test to the occurrence of the first agonistic behavior) were measured as indices of agonistic behavior. Two-way repeated measures ANOVA revealed significant differences in TAF and latency between aggressors and opponents in both the behavioral tests. In the R-I test, the TAF of aggressors significantly increased from 8 to 20 days of age, and the latency significantly decreased from 8 to 24 days of age. In the SI test, however, the TAF of aggressors significantly increased and the latency significantly decreased only from 16 to 20 days of age. When the criterion of high agonistic behavior was defined as the TAF, where aggressors showed more than 30 times of TAF and the opponents did less than one-third TAF of aggressors, the aggression establishment rate (AER), which is equal to the number of aggressors showing high agonistic behavior per total behavioral trials, was significantly higher in the R-I test than in the SI test. These results suggest that the R-I test, rather than the SI test, is an effective tool for monitoring agonistic behavior of layer chicks.

Behavioural and Hormonal Stress Responses to Social Separation in Ravens, Corvus corax

Social life is profitable, but it facilitates conflicts over resources and creates interdependence between individuals. Separating highly social animals triggers intense reactions aimed at re-establishing lost connections. Less is known, however, about behavioural and physiological responses to separation in socially facultative species, where individuals temporarily form groups and may subsequently leave them. Non-breeding common ravens (Corvus corax) gather in large numbers at feeding and roosting sites, but otherwise spend time seemingly solitary or in small subgroups. We here studied how ravens cope with being socially isolated, and investigated the life characteristics that might explain potential individual differences. For this, we individually separated captive subadult ravens (n = 25) and housed them in physical and visual isolation from their group members across 4 d. During the separation period, we collected behavioural data and measured the amount of immunoreactive corticosterone metabolites from bird droppings to assess the ravens' physiological stress response. We found behavioural indicators of stress at the start of the separation, when ravens showed higher levels of tension than of comfort - a pattern that reversed at the end of the separation. Furthermore, we found that the upbringing of ravens affected their behaviour during separation. Hand-raised birds produced more vocalisations in the beginning of the separation, and were less active at the end, while the reverse pattern occurred with parent-raised ravens. Contrary to our predictions, we did not find differences in hormonal responses between the beginning and end of the separation period or any link between hormonal responses and behaviours. Ravens' behavioural responses to social separation stress seem to be dependent on their arousal states, although possible links with hormonal reactions remain unclear. Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early-life experiences.

Central Injection of Glucose Modifies Behavior, Amino Acid and Monoamine Metabolism in Neonatal Chicks under Acute Stressful Conditions

The effect of intracerebroventricular (i.c.v.) injection of a wide range of glucose concentrations on the behavioral response, central amino acid and monoamine contents was investigated in chicks exposed to a social isolation stressful condition. The chicks were given an i.c.v. injection of 0.21, 0.42, 0.84, and 1.68 µmol of D-glucose, and then behavioral changes were observed over 10 min. The behavioral stress response was dose-dependently decreased and calm behavior was increased by i.c.v. administration of glucose. In the diencephalon, glutamine was positively correlated, whereas glycine was negatively correlated with the dose of glucose. In the telencephalon, the dopamine metabolite and dopamine turnover rates were positively correlated, whereas dopamine was negatively correlated with doses of glucose. In the plasma, isoleucine and hydroxyproline were positively correlated with the dose of glucose, and several amino acids were also influenced by glucose levels.

These results suggest that the possible pathways of the sedative effect of glucose include: (1) amino acids synthesized from injected glucose, which can induce the sedative and/or hypnotic effects; (2) amino acids modified by injected glucose transported in the brain from the peripheral tissues; and (3) injected glucose-induced decreases in brain dopamine levels. In conclusion, these changes induced by central glucose interact and induce the sedative effect in neonatal chicks.

Social motivation in Japanese quail coturnix coturnix japonica chicks selected for high or low levels of treadmill behaviour

Social motivation (as measured by a visually isolated chick's tendency to establish visual contact with, move towards and remain in proximity to a group of conspecifics) was assessed in lines of Japanese quail which had been selected for high (HSR line) or low (LSR line) levels of an index of treadmill behaviour which combined the tendency to run towards conspecifics with the tendency to move away from them. HSR line chicks peeded sooner and more frequently before establishing visual contact with conspecifics and spent more time close to conspecifics after visual contact had been established than LSR line chicks. HSR line chicks also tended to have shorter latencies to establish visual contact with conspecifics, jump more and interact more with conspecifics than LSR chicks. It is suggested that these results indicate that selection for treadmill behaviour, which is considered to be a measure of social reinstatement tendencies, has influenced overall levels of social motivation. Furthermore, it would also appear that the phenotypic differences between the HSR and LSR lines are relatively intensive to genotype x environment interactions.

Effect of group disruption on social behaviour in lines of Japanese quail (Coturnixjaponica) selected for high or low levels of social reinstatement behaviour

Japanese quail of lines selected for high (HSR) or low (LSR) levels of social reinstatement (SR) behaviour were reared in groups of three. At 3 and 6 weeks of age, one group member was replaced with an unfamiliar conspecific bird. Behaviour following introduction of the intruder was similar at both ages. Quail of both lines spent more time immobile after introduction of the intruder than before its introduction. In the LSR, but not the HSR line, inter-individual distances between intruders and other chicks, were greater than those between familiar chicks. Birds of both lines pecked more between unfamiliar than between familiar birds. Pecks, not associated with escape or avoidance by the pecked bird, were more frequent in HSR groups. Selection for HSR behaviour appears to have increased non-aggressive exploration of intruder whereas selection for LSR behaviour has decreased interest in or increased shunning of intruders.

Behavioural and hormonal effects of social isolation and neophobia in a gregarious bird species, the European starling (Sturnus vulgaris)

Separating gregarious individuals from their group members often results in behavioural and physiological changes, like increased levels of corticosterone. Testosterone and corticosterone, in particular, have been implicated in the response of mammals to novelty. Data in birds are, however, rare. The presence or absence of group members may also influence an individual's response to novel stimuli. We assessed the behaviour and hormonal response of European starlings (Sturnus vulgaris) to a novel object in two different situations and seasons: each starling was tested when separated and when in contact with its group members in May/June (breeding season) and again in September/October (non-breeding season). Starlings are gregarious throughout the year, but as foraging flocks are small during the breeding season and large during the non-breeding season, we assumed that non-breeding starlings would be more affected by social isolation. Overall, starlings had higher levels of corticosterone, lost more body mass, and were more active when they were separated from their group. Isolated individuals, however, did not show a greater neophobic response than individuals in the presence of their group members in either season. Circulating levels of testosterone and corticosterone were higher after a test with novel object than after a test with only the familiar feeding dish in both sexes and seasons. However, control tests for handling effects confirmed only the increase in testosterone. Our study shows that social isolation is stressful for unrelated and unpaired members of a wild flocking bird species and demonstrates that novelty can lead to a rise in testosterone in birds.

Behavioural and endocrine fear responses in Japanese quail upon presentation of a novel object in the home cage

Most tests used to study fear in birds involve transferring them to a novel environment, which constitutes a bias in studies aiming at identifying the neural correlates of a specific fear-inducing situation. In order to investigate fear in birds with minimum interference by humans, behavioural and endocrine responses to the presentation of a novel object in the home cage were investigated in two lines of Japanese quail divergently selected for long or short duration of tonic immobility, a behavioural index of fear. Presentation of the novel object induced typical fear responses (avoidance of the object, increased pacing and increased plasma corticosterone levels) that were similar in the two lines of quail. Presentation of a novel object in the home cage thus appears to be a suitable stimulus to induce fear reactions in quail, with minimum interference from other motivational systems. The fact that quail of both lines reacted similarly in this test, while they are known to differ greatly in their behavioural responses to other fear-inducing tests, illustrates the multidimensional nature of fear.

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.

Behavioral and adrenocortical responses to mate separation and reunion in the zebra finch

The adaptive value of social affiliation has been well established. It is unclear, however, what endogenous mechanisms may mediate affiliative behavior. The Australian zebra finch (Taeniopygia guttata) breeds colonially and adults maintain lifelong pair bonds that may be disrupted in the wild due to high mortality rates. Many of its natural, social behaviors are maintained in laboratory conditions, making this species well suited for studying the mechanisms of affiliation. This study examines the behavioral and neuroendocrine responses to pair mate separation and reunion in zebra finches. We measured plasma corticosterone (CORT) and behavioral changes following separation from a pair bonded mate, and again upon reintroducing the mate or an opposite-sex cagemate. Plasma CORT concentrations were: (1). elevated during pair mate separation, even in the presence of other same-sex individuals, and (2). reduced to baseline upon reunion with the pair mate but not upon re-pairing with a new opposite-sex partner. These findings show that zebra finches exhibit hormonal responses to separation and reunion specifically with a bonded pair mate and not with other familiar conspecifics. In addition, alterations in behavior during separation and reunion are consistent with monogamous pair bond maintenance. This study presents evidence for adrenocortical involvement in avian pair bonding, and for hypothalamic-pituitary-adrenal activation in response to an ecologically relevant social stressor.

Assessment of the analgesic effects of ketoprofen in ducks anesthetized with isoflurane

OBJECTIVE

To determine whether administration of ketoprofen would have analgesic effects in spontaneously breathing ducks anesthetized with isoflurane.

ANIMALS

13 healthy adult wild-strain Mallard ducks.

PROCEDURE

Each duck was anesthetized twice in a crossover study design with 6 days between randomized treatments. Ducks were given ketoprofen (5 mg/kg, IM) or saline (0.9% NaCl) solution after a constant plane of anesthesia was established. Analgesia was assessed by measuring heart and respiratory rates and duration of application of a noxious stimulus. The noxious stimulus was applied 30, 50, and 70 minutes after drug administration and was maintained until gross purposeful movements were seen or for a maximum of 5 seconds.

RESULTS

At all 3 evaluation times, heart rate increases in response to the noxious stimulus were greater when ducks were given saline solution than when they were given ketoprofen. The increase in respiratory rate in response to the noxious stimulus was greater when ducks were given saline solution than when they were given ketoprofen only 70 minutes after drug administration. When ducks were given ketoprofen, duration of the noxious stimulus was significantly longer 50 and 70 minutes, but not 30 minutes, after drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketoprofen reduced the increases in heart and respiratory rates associated with application of a noxious stimulus in spontaneously breathing adult Mallard ducks anesthetized with isoflurane delivered at approximately 2.9%, suggesting that ketoprofen had analgesic effects in these ducks. The onset of analgesic effects may be longer than 30 minutes in some ducks.

Dissociation of stress behaviors in the chick social-separation-stress procedure

Separation from conspecifics in chicks produces an increase in distress vocalizations and a decrease in response to a noxious stimulus (stress-induced analgesia). This study questioned the relative contributions of novelty to the test chamber and social separation in mediating these stress responses. Eight-day-old chicks were tested either in isolation or in the presence of two social companions for a 3-min observation period in which distress vocalizations were recorded as well as the frequency of footlifts in response to a 50-microl injection of 0.10% formalin into the plantar surface of the footpad. In Expt. 1, chicks received six, 3-min test chamber habituation trials (vs. no habituation) one per day before testing; in Expt. 2, chicks were tested with mirrors placed in the chambers (vs. no mirrors). In both studies, isolated chicks in control groups (i.e., no habituation or no mirror) exhibited increased distress vocalizations and decreased nociceptive responses. In Expt. 1, habituation to the test chamber attenuated stress-induced analgesia but did not affect distress vocalizations. In Expt. 2, placement of mirrors in the test chamber attenuated distress vocalizations but did not affect stress-induced analgesia. These findings demonstrate a dissociation of stress behaviors in the chick social-separation-stress procedure: the stress-induced analgesia response is primarily mediated by novelty to the test apparatus while the distress vocalizations response is mediated by separation from conspecifics.

Sex differences in central benzodiazepine receptor densities and circulating corticosterone release after acute stress in broiler chicks

The purpose of the study was to determine the effect of sex on central benzodiazepine receptor (CBR) and serum corticosterone (CS) responses to an acute stressor in broiler chicks. Birds were housed in ten mixed-sex groups of eight chicks per cage. At 15 d of age, chicks were taken from a randomly selected cage and blood was immediately sampled (undisturbed controls), or they were taken from the same cage and immersed up to their necks in warm water (partial water immersion, PWI) for 15 min before blood was sampled. After blood sampling, forebrains were dissected for preparation of membranes, and bird sex was determined by gonadal inspection. Serum CS levels were determined by a competitive protein-binding assay. CBR densities were determined by radiolabeled receptor binding assay. There were no sex differences in serum CS levels or benzodiazepine receptor densities in controls. Exposure to PWI significantly increased (P < 0.01) circulating CS levels in both sexes, and this elevation was more pronounced (P < 0.01) in males than in females. Male, but not female, chicks also showed a significant stressor-induced increase (P < 0.01) in CBR densities. These findings showed sexual differences in acute, stressor-induced benzodiazepine and adrenocortical responses that suggest broiler males are more stress-susceptible than females.

Individual variation in corticosterone secretion in laying hens

1. Plasma corticosterone responses to a handling and isolation stressor were measured in laying hens once, before two groups were mixed into a single larger group, and again after the groups were mixed. Hens were bled before the stressor was applied and within 3 min of removal from groups (0 min sample), and again 15 and 45 min later 2. Social interactions were recorded throughout the experiment using continuous, all-occurrences sampling during group observations and the social rank index of each hen was calculated. 3. Plasma corticosterone was low immediately after birds were first picked up and sampled on each occasion, and rose to a peak after repeated handling, 15 min later. It then declined and was almost back to basal levels 40 min after first handling. 4. Corticosterone responses were greater 6 d before mixing (first day of sampling) than they were 1, 7 or 21 d after mixing. Corticosterone concentrations and responses were not elevated 1 d after the two groups of hens were mixed. 5. Variation in corticosterone concentrations and responses within and between hens was quantified by calculating coefficients of variation of corticosterone concentrations and areas under corticosterone response curves. Variation tended to be less within than between hens. 6. There was a transient increase in aggressive interactions immediately after mixing. One bird was clearly dominant in each observed dyadic interaction and hierarchies tended to strong linearity in all groups. Social rank was not related to corticosterone concentrations or responses. 7. Area under the corticosterone response curve can be used to compare differences between and within laying hens in their responsiveness to a handling and isolation stressor.

Effects of an acute stressor on fear and on the social reinstatement responses of domestic chicks to cagemates and strangers

Genetic selection for appropriate levels of sociality (motivation to be with conspecifics) could benefit poultry welfare and performance. Runway tests that require chicks to traverse a corridor in order to reach other chicks in a goal box are commonly used to measure this behavioural trait. However, we need to determine if the chicks' responses in such tests are sensitive to certain experiential variables before we can recommend possible selection criteria for future breeding programmes. The present study focused on fear and on the identity of the stimulus birds. Broiler chicks either remained undisturbed or were exposed to an acute stressor (mechanical restraint) before their tonic immobility fear responses were measured 1h later in Experiment 1. Exposure to the stressor significantly prolonged tonic immobility and, hence, presumably, underlying fear levels. In Experiment 2, the responses of stressed chicks and undisturbed controls were assessed when they were tested individually in a runway with a goal box containing either familiar or unfamiliar chicks of the same age. Our finding that stressed chicks emerged from the start box sooner and spent longer near the stimulus birds suggests that exposure to a frightening event increased social reinstatement motivation. Furthermore, social affiliation was more pronounced when the goal box contained familiar cagemates rather than strange chicks, regardless of prior treatment. This finding demonstrates that broiler chicks that were housed in groups of twelve can discriminate between familiar and unfamiliar conspecifics encountered in novel surroundings. Thus, sociality was positively associated with fearfulness and broilers clearly showed social discrimination in runway tests. These findings highlight the dangers of disregarding variables, such as fear and the capacity for social recognition in tests of social motivation. We strongly recommend that exposure to frightening events prior to test should be avoided and that the identity of the birds in the runway goal box should be standardized, i.e. either familiar or unfamiliar, and noted.

T-maze behaviour in broiler chicks is not sensitive to right-left preferences, test order or time-of-day

There is substantial individual variation in the time taken by broiler chicks to traverse a T-maze and thereby reinstate visual contact with their companions. Chicks completing this task quickly (high performance, HP) subsequently grew faster in the laboratory and on farm, exhibited greater sociality, and showed less pronounced adrenocortical responses to a partial water immersion stressor than did their slower (low performance, LP) counterparts [Marin, R.H., Jones, R.B., 1999. Latency to traverse a T-maze at 2 days of age and later adrenocortical responses to an acute stressor in domestic chicks. Physiol. Behav. 66, 809-813.; Marin, R.H., Arce, A., Martijena, I.D., 1997. T-maze performance and body weight relationship in broiler chicks. Appl. Anim. Behav. Sci. 54, 197-205.; Jones, R.B., Marín, R.H., García, D.A., Arce, A., 1999. T-maze behaviour in domestic chicks: a search for underlying variables. Anim. Behav. 58, 211-217.]. Given its simplicity, rapidity and non-invasiveness, the T-maze test might represent a commercially attractive selection criterion for future breeding programmes if this behavioural trait exhibits sufficient genetic variability. However, it is first necessary to ensure that performance in the T-maze is not sensitive to potentially confounding variables, such as existing preferences to turn right or left at the junction of the maze, the order of testing, or the time of day. In the present study, 240 newly hatched, mixed-sex broiler chicks (Cobb) were randomly allocated to 12 groups of 20 upon receipt. When they were 2 days of age a group of 20 chicks was placed in the brood area of each of two T-mazes at 0830 h; the brood areas were positioned on either the right or the left sides of the mazes. After acclimatisation, one chick from each group was placed in the isolation chamber of the T-maze and we recorded the time it took to traverse the maze. This procedure was repeated until all 20 chicks and all 12 groups had been tested. The locations of the brood areas were rotated after each block of 20 tests. Testing was completed in the same day and two groups were tested at each of the following times: 0900, 1030, 1200, 1330. 1500, and 1630 h. Analyses of variance (ANOVA) revealed no detectable effects of: positioning the brood area on the right or the left side of the T-maze (F(1,200)=0.06, P<0.80), test order (F(19,200)=0.48; P<0.96), or time-of-day (F(5,234)=0.44; P<0.81). These findings strongly suggest that the future classification and possible selection of broiler chicks according to their T-maze responses are unlikely to be confounded by right-left preferences, test order, or the time of day.

Timidity in Japanese quail: effects of vitamin C and divergent selection for adrenocortical response

Male Japanese quail chicks of two genetic lines selected for low (LS) or high (HS) adrenocortical responses to mechanical restraint were housed in mixed-line groups of 24 in four compartments of a multitier brooder battery at 20 days of age. Quail in two of the four compartments were given vitamin C (ascorbyl-2-polyphosphate, APP, 1 g L-ascorbic acid/L) solution for 48 h, whereas the other birds received untreated tap water as usual before they were tested at 23 days of age. At test, each quail was placed individually in a dark, sheltered compartment of an emergence box and allowed 1 min to acclimatise before a door was raised allowing access to an illuminated and exposed area. Vocalisation and the latencies to head and full emergence were then recorded to measure its fear levels. More LS quail vocalised than did HS ones. They also emerged more rapidly from the sheltered compartment into the illuminated one than HS birds. These findings further support our hypothesis that decreased fearfulness has accompanied genetic selection for reduced adrenocortical responsiveness. Treatment with APP reduced the latency to emerge fully into the exposed compartment, and there were no line x treatment interactions. These results suggest that vitamin C supplementation alleviated fearfulness, regardless of existing line differences in this behavioural trait.

T-maze behaviour in domestic chicks: a search for underlying variables

We investigated whether contrasting T-maze behaviour shown by domestic chicks, Gallus gallus domesticus, of a broiler strain reflected underlying differences in their general activity levels, fearfulness or sociality. The time taken by 2-day-old chicks to traverse a T maze and thereby regain visual contact with their companions was measured. Chicks were categorized according to whether they completed this task quickly (HP, high performance, <25 s) or slowly (LP, low performance, >75 s) and then housed in same-category groups, each of eight chicks. In experiment 1, we compared the numbers of HP and LP chicks showing certain home cage behaviours (ambulation, standing, resting, maintenance, pecking, preening). No significant differences were found. In experiment 2, we compared the behaviour of HP and LP chicks in two tests of sociality (home cage proximity, runway) and in two tests of fear (emergence, tonic immobility). The HP chicks stayed closer together in the home cage than did their LP counterparts and they spent significantly longer near a goal box containing conspecifics in the runway than did LP ones. Conversely, there were no significant differences between HP and LP chicks in their latency to emerge from a sheltered area into an exposed and, hence, potentially frightening one or in their tonic immobility fear reactions. These findings suggest that contrasting T-maze performance was unlikely to have reflected differences in underlying activity levels or in fearfulness. Conversely, individual variation in underlying sociality was probably an influential variable. Copyright 1999 The Association for the Study of Animal Behaviour.

Long-term memory for a spatial task in young chicks

Two-day-old chicks, Gallus gallus domesticus, were faced with a spatial task requiring them to make a detour around a U-shaped barrier in order to join a group of conspecifics placed beyond it. Chicks made one detour trial, and were then retested after delays of 30 min, 3 h and 24 h. When retested, the chicks took significantly less time to make the detour, even at 24 h. Chicks that failed to solve the task on the first trial within the time limit (600 s) took as long as naive chicks, when tested again 24 h later, suggesting that long-term memory for the task requires a form of one-trial learning. Since many chicks chose the same direction of detour on both the first trial and the retest, they may have simply shown a stereotyped preferential response. In a further experiment to test this possibility, we used a more complex version of the apparatus: the direction of detour first chosen by the chick was always blocked, and a subsequent detour in the opposite direction was required to complete the task. This time, chicks did not choose the same direction on the first test and when tested 24 h later. However, they proved able to remember the correct direction for at least 24 h if they were allowed to learn the correct path in a series of five trials. Copyright 1999 The Association for the Study of Animal Behaviour.

Behavioral, cardiac and cortisol responses to brief peer separation and reunion in cattle

Behavioral, cardiac, and adrenal responses of heifers to short-term isolation and to subsequent reunion with familiar or nonfamiliar conspecifics were measured. Two groups of heifers were studied according to their different social reactivity: Aubrac heifers (n = 12) reared under suckler conditions and Friesian heifers (n = 12) reared under dairy management. Because these two groups could also react differently to human beings, testing social isolation was realized by removing pen mates without handling the subject. Moreover, heifers were tested in confinement to avoid an alteration of the cardiac response to isolation by an excessive motor activity. Although physical restraint can influence the reactions, this effect is assumed to be weak because heifers had been exposed to the experimental procedures, including confinement for 3 days before isolation test, in addition to brief periods of physical restraint occurring regularly according to rearing practices. Results show that social separation induced struggling and large increases in vocalization, heart rate, and plasma cortisol concentrations in all heifers. Except for vocalization, these effects were more severe in Aubrac than in Friesian heifers. For all heifers, isolation-induced distress was positively correlated with the duration of social contacts they engaged with the pen mates prior to separation. Behavioral responses, i.e., struggling and vocalization, decreased when conspecifics were brought back, independently of their familiarity to the subject. In contrast, the heart rate decline induced by the entrance of conspecifics was more pronounced in response to reintroduction of pen mates. These findings indicate that social isolation is a severe psychological stress in cattle and that the mere sight of conspecifics reduces behavioral distress regardless of peer identity. The isolation-induced distress depends on the genetic and rearing backgrounds of the heifers without allowing to differentiate their respective effects.

Hypothalamic-pituitary-adrenal responses to brief social separation

Involuntary separation from close social companions is widely held to lead to pathophysiological outcomes. Presumably, the relationship with, or category of, the separated individual determines the nature of the physiological response. Here, experiments examining the consequences of brief involuntary separation on the activity of the stress-responsive hypothalamic-pituitary-adrenal (HPA) system are reviewed. Only those studies designed specifically to assess the effect of the absence of the social partner are considered. Evidence for HPA activation in response to social separation has been obtained in a number of species; yet, many studies find no effect of separation of affiliative partners on HPA activity. The occurrence of an HPA response to separation does not appear to be related to the phylogenetic position or cognitive capacity of the species studied, nor is it a universal response to mother-infant separation. Rather, it is suggested that the pattern of results can be largely understood in the context of attachment. Separation of partners exhibiting signs of emotional attachment leads to an immediate and persistent HPA response, whereas separation of partners that are affiliative, but do not exhibit attachment, has little or no effect on HPA activity.

Influences of blood sampling procedures on basal hypothalamic-pituitary-adrenal hormone levels and leukocyte values in rhesus macaques (Macaca mulatta)

The influences of housing location and temporal factors on the results of blood sampling were examined to determine their contributions to levels of hypothalamic-pituitary-adrenal hormones, as well as leukocyte subset counts from peripheral blood in rhesus monkeys. Differences in housing location and the amount of room disturbance associated with blood sampling have a significant impact on cell counts, but not on ACTH or cortisol levels.

Effects of ascorbyl-2-polyphosphate on adrenocortical activation and fear-related behavior in broiler chickens

The effects of supplemental ascorbyl-2-polyphosphate (APP) on adrenocortical function and underlying fearfulness in broiler chickens were assessed in a number of test situations. Chicks pretreated for a minimum of 24 h with APP (1,000 ppm equivalents of L-ascorbic acid) in their drinking water or with no APP (tap water controls; CON) had blood samples taken immediately following water treatment and again after exposure to a capture and cooping stressor for 10 min. First, although the cooping stressor markedly increased plasma corticosterone concentrations, pretreatment with APP failed to attenuate this adrenocortical response. Second, APP-treated chicks showed less freezing and vocalized sooner in an open field (novel environment) than did controls. They also showed nonsignificant tendencies toward accelerated and enhanced ambulation. Third, supplementation with APP reduced the duration of the birds' tonic immobility fear reactions. Collectively, these behavioral effects are indicative of dampened fear. The apparent reduction of nonspecific, underlying fearfulness by APP treatment may have important implications for poultry welfare and performance.

Short-latency stressor effects on tonic immobility fear reactions of Japanese quail divergently selected for adrenocortical responsiveness to immobilization

Despite evidence for a positive association between adrenocortical activation and fearfulness, the effects of chronic (12 to 20 h) exposure to stressful stimulation on the fear reactions of Japanese quail genetically selected for high (HS) or low (LS) plasma corticosterone response to immobilization stress are not straightforward. The present study examined tonic immobility fear responses in quail of both lines that, immediately prior to testing, either had been allowed to remain undisturbed or had been exposed to an acute stressor similar to that used in the selection program (i.e., a short-latency stressor; 5 min of immobilization). Tonic immobility responses were generally more pronounced in quail of the HS line than the LS line, and they were exaggerated in both lines after exposure to stress treatment. The findings provide further support for the suggestion that selection for exaggerated or reduced adrenocortical responsiveness may have been accompanied by a concomitant and unconscious effect on underlying fearfulness.

Responses to isolation in Japanese quail genetically selected for high or low sociality

The adrenocortical, behavioral, and leucocytic responses to isolation, for 1, 3, or 72 h, of 7-10-day-old Japanese quail chicks, of lines selected for high (HSR) or low (LSR) levels of social reinstatement (SR) behavior, were studied. Isolation had no effect on plasma corticosterone levels of heterophil/lymphocyte measures in LSR line chicks. Conversely, circulating corticosterone levels were increased after 1 h of isolation in the HSR line, although they fell to control levels thereafter. Heterophil/lymphocyte ratios of HSR line chicks were also increased after 3 h of isolation but decreased to control levels thereafter. Isolated HSR line chicks were consistently more active and showed more peeping and jumping than LSR line chicks in which sitting and lying were more frequent. However, no such behavioral divergence was observed when HSR and LSR line chicks were housed in same-line groups. These results indicate that selection for SR behavior has influenced both underlying social motivation and responses to short-term isolation. Social separation appeared to be more stressful for HSR than LSR line chicks.

Research note: open-field behavior of Japanese quail chicks genetically selected for low or high plasma corticosterone response to immobilization stress

Open-field behavior was examined in Japanese quail chicks genetically selected for either reduced (LS, low stress) or exaggerated (HS, high stress) plasma corticosterone response to immobilization stress. Chicks of the LS line showed less freezing and ambulated sooner than did their HS counterparts. These findings suggest that exposure to an open-field or novel environment elicited less fear in LS than in HS chicks. They also support the suggestion that fearfulness and adrenocortical activation are positively associated and indicate that selection for differential adrenocortical responsiveness exerted concomitant effects on fear-related behavior.

Effects of blood sampling on plasma concentrations of corticosterone and glucose in laying hens caged in groups

1. The effects of taking a blood sample from one bird in a caged group on plasma concentrations of corticosterone and glucose in birds from its own group and birds from other groups were investigated. 2. Two blood sampling protocols were used: successive (all birds within a group were sampled one immediately after another) and alternative (birds from different groups were sampled one after another until all birds in all groups had been sampled). 3. Neither sampling protocol nor between or within group sampling rank was related to plasma concentrations of corticosterone and glucose. 4. The time taken to remove a blood sample (generally more than 45 s but less than 2 min) did not influence circulating corticosterone and glucose. 5. In individual birds plasma concentrations of corticosterone and glucose were poorly correlated with one another. 6. It is concluded that it is possible to take blood samples from a bird, kept in a group, without affecting plasma concentrations of corticosterone and glucose in other birds from that group or in birds from other groups in other cages.