Changes in serum cortisol reveal functional differences in frustration-induced chain chewing in pigs

An enriched maternal environment and stereotypies of sows differentially affect the neuro-epigenome of brain regions related to emotionality in their piglets

Epigenetic mechanisms are important modulators of neurodevelopmental outcomes in the offspring of animals challenged during pregnancy. Pregnant sows living in a confined environment are challenged with stress and lack of stimulation which may result in the expression of stereotypies (repetitive behaviours without an apparent function). Little attention has been devoted to the postnatal effects of maternal stereotypies in the offspring. We investigated how the environment and stereotypies of pregnant sows affected the neuro-epigenome of their piglets. We focused on the amygdala, frontal cortex, and hippocampus, brain regions related to emotionality, learning, memory, and stress response. Differentially methylated regions (DMRs) were investigated in these brain regions of male piglets born from sows kept in an enriched vs a barren environment. Within the latter group of piglets, we compared the brain methylomes of piglets born from sows expressing stereotypies vs sows not expressing stereotypies. DMRs emerged in each comparison. While the epigenome of the hippocampus and frontal cortex of piglets is mainly affected by the maternal environment, the epigenome of the amygdala is mainly affected by maternal stereotypies. The molecular pathways and mechanisms triggered in the brains of piglets by maternal environment or stereotypies are different, which is reflected on the differential gene function associated to the DMRs found in each piglets' brain region . The present study is the first to investigate the neuro-epigenomic effects of maternal enrichment in pigs' offspring and the first to investigate the neuro-epigenomic effects of maternal stereotypies in the offspring of a mammal.

Changes in Stereotypies: Effects over Time and over Generations

Simple Summary

Herein, we propose that there should be discussion about the function and effects of stereotypies in relation to the time during which they are shown. In the first stages, stereotypies may help animals deal with challenges. However, behavior can potentially alter the brain, impairing its function due the absence of a diverse repertory, and change brain connections, neurophysiology and later neuroanatomy. The neuroanatomical changes in individuals showing stereotypies could be an effect rather than a cause of the stereotypy. As a consequence, studies showing different outcomes for animal welfare from stereotypy expression could be due to variation in a timeline of expression. Stereotypies are widely used as an animal welfare indicator, and their expression can tell us about psychological states. However, there are questions about the longer-term consequences if animals express stereotypies: do the stereotypies help in coping? During the prenatal period, stereotypic behavior expressed by the mother can change the phenotype of the offspring, especially regarding emotionality, one mechanism acting via methylation in the limbic system in the brain. Are individuals that show stereotypies for shorter or longer periods all better adjusted, and hence have better welfare, or is the later welfare of some worse than that of individuals that do not show the behavior?

Abstract

Stereotypies comprise a wide range of repeated and apparently functionless behaviors that develop in individuals whose neural condition or environment results in poor welfare. While stereotypies are an indicator of poor welfare at the time of occurrence, they may have various consequences. Environmental enrichment modifies causal factors and reduces the occurrence of stereotypies, providing evidence that stereotypies are an indicator of poor welfare. However, stereotypy occurrence and consequences change over time. Furthermore, there are complex direct and epigenetic effects when mother mammals that are kept in negative conditions do or do not show stereotypies. It is proposed that, when trying to deal with challenging situations, stereotypies might initially help animals to cope. After further time in the conditions, the performance of the stereotypy may impair brain function and change brain connections, neurophysiology and eventually neuroanatomy. It is possible that reported neuroanatomical changes are an effect of the stereotypy rather than a cause.

Behavioral neuroscience of psychological pain

Pain is a common word used to refer to a wide range of physical and mental states sharing hedonic aversive value. Three types of pain are distinguished in this article: Physical pain, an aversive state related to actual or potential injury and disease; social pain, an aversive emotion associated to social exclusion; and psychological pain, a negative emotion induced by incentive loss. This review centers on psychological pain as studied in nonhuman animals. After covering issues of terminology, the article briefly discusses the daily-life significance of psychological pain and then centers on a discussion of the results originating from two procedures involving incentive loss: successive negative contrast-the unexpected devaluation of a reward-and appetitive extinction-the unexpected omission of a reward. The evidence reviewed points to substantial commonalities, but also some differences and interactions between physical and psychological pains. This evidence is discussed in relation to behavioral, pharmacological, neurobiological, and genetic factors that contribute to the multidimensional experience of psychological pain.

Repeated handling of pigs during rearing. I. Refusal of contact by the handler and reactivity to familiar and unfamiliar humans

Pigs housed in groups received different handling treatments for 40 d until slaughter age. Pigs of the human interaction (HI) and refusal of contact (RC) groups were individually introduced into a pen each day, where they remained for 3 min in the presence of a squatted handler. The handler tried to increase progressively physical reciprocal interactions with the HI pigs using eye and body contact and voice. The handler remained immobile and avoided eye contact and use of voice with RC pigs. These pigs were pushed away when they touched the handler. Control pigs remained in their home pens. Over sessions, HI pigs progressively increased physical interactions with the handler, up to 35% of their time. The RC pigs were motivated to interact with the handler as they tried to establish physical contact with the handler throughout the experiment. They increased levels of locomotion, rubbing, immobility, and snout contact with the wall, suggesting that they were frustrated by the refusal of contact. At the end of the experimental period, all pigs were subjected to three human exposure tests, where pigs were exposed to the handler and two other persons, one of which was unfamiliar, in a Latin square design. During this test, behavior of the humans was the same as for the RC treatment. The HI pigs discriminated between the handler and the other persons as indicated by their increased approach behavior towards the handler. Part of the prior handling experience was generalized to other humans as indicated by higher levels of proximity of HI and RC pigs with the different persons compared with controls. Physical contact with the human was associated with increased heart rates. Two possibilities are that these two characteristics are part of a general behavioral/physiological reactive profile, or that contact with humans provokes an arousal or emotional response. Despite this, behavioral data show that pigs are motivated to be in physical contact with a handler, even when the handler consistently refuses contact.

Introduction of Foreign Female Asian Elephants (Elephas Maximus) Into an Existing Group: Behavioural Reactions and Changes in Cortisol Levels

The present study examined the extent to which the introduction of three female Asian elephants (aged 3, 11, and 27 years) into a group of 1.4 (1 male, 4 female) elephants at Münster zoo, Germany, affects the behaviour and urinary Cortisol levels of the animals involved. At Münster, only the females were monitored — the bull was mainly kept separate. Behavioural observations were carried out before transfer and during the six-month period following transfer, and urine samples were collected regularly from each elephant during the whole observation period. All elephants showed behavioural changes to the process of introduction. The transferred animals increased their social behaviour after arrival in the foreign zoo. Two of them showed an increase in stereotypies and one a reduction in stereotypies. The elephants at Münster reacted with decreased frequencies of stereotypies and increased frequencies of social behaviour and manipulation/exploration behaviour. Six months after transfer, three of the four elephants at Münster and one of the three transferred elephants showed nearly the same behavioural activity pattern as before transfer. One female still showed elevated stereotypic behaviour. From the four elephants in which Cortisol measurements could be reliably performed (two of the transferred elephants and two elephants at Münster), only one individual at Münster responded to the process of introduction with a short-term elevation in urinary Cortisol levels. One elephant showed a negative correlation between locomotion and Cortisol levels and one a positive correlation between stereotypies and Cortisol levels. Taken together, the results suggest that transfer and introduction caused some stress responses in the elephants, but that stress was neither prolonged nor severe. Serious welfare problems may have been prevented through individual behavioural coping mechanisms and former experience with stressful situations.

The Putative Welfare-Reducing Effects of Preventing Equine Stereotypic Behaviour

The common practice of preventing equine stereotypic behaviour in the UK may be of concern, from a welfare perspective, if these behaviours constitute a coping response to a suboptimal environment. The aim of this study was to assess the putative function of these behaviours by measuring behavioural and physiological parameters i) before and after stereotypy prevention; ii) before and after stereotypy performance; and iii) in response to opiate antagonist (naloxone) administration.

The crib-strap significantly (P = 0.05) elevated mean plasma Cortisol levels in crib-biting horses; a similar, although not significant trend (P = 0.07) was also observed for the weaving group during the anti-weave bar treatment. Both crib-strap and anti-weave bar significantly (P < 0.05) elevated plasma Cortisol levels in the control horses. Although the latter result prevented a definite conclusion being drawn about the function of equine stereotypies, the results did indicate that the use of the crib-strap and anti-weave bar is stressful to the horse.

Plasma Cortisol level was significantly (P = 0.04) higher immediately prior to the onset of stereotypy followed by a significant reduction post-stereotypy. This suggested that both crib-biting and weaving have a coping function to reduce stress levels in the animal.

Naloxone significantly reduced crib-biting by 84 per cent (P = 0.05) but it did not reduce weaving behaviour, indicating that crib-biting is a reward behaviour. However, resting behaviour was also significantly (P = 0.02) increased in crib-biting horses, suggesting that the stereotypy reduction was due to a sedative effect of the opiate antagonist. The latter was not measured, however, in control or weaving animals, and thus may be interpreted differently. The welfare implications of these results are discussed.

Adrenalectomy eliminates the extinction spike in autoshaping with rats

Experiment 1, using rats, investigated the effect of adrenalectomy (ADX) on the invigoration of lever-contact performance that occurs in the autoshaping situation after a shift from acquisition to extinction (called the extinction spike). Groups of rats with ADX or sham operations were trained under spaced and massed conditions [average intertrial intervals (ITI) of either 15 or 90 s] for 10 sessions and then shifted to extinction. ADX did not affect acquisition training but it eliminated the extinction spike. Plasma corticosterone levels during acquisition were shown in Experiment 2 to be similar in rats trained under spaced or massed conditions. Adrenal participation in the emotional arousal induced by conditions of surprising nonreward (e.g., extinction) is discussed.

Consequences of Surprising Reward Omissions

A surprising reward omission (SRO) occurs when an appetitive reinforcer is not presented (or it is reduced in magnitude or quality) even though there are signals for its impending presentation. Evidence supporting the hypothesis that SROs produce an aversive emotional reaction with physiological and behavioral consequences is reviewed. SROs are followed by pituitary–adrenal activation; changes in immune function; odor emissions in rodents; distress vocalizations in rodents and primates; and increases in locomotion, aggressive behavior, drinking, and eating. SROs can support the acquisition of new escape responses and invigorate previously acquired responses. The review identifies common aspects of these phenomena and areas in which more research is needed.

Schedule-induced masseter EMG in facial pain subjects vs. no-pain controls

Empirical reports suggest that oral habits (e.g., teeth clenching) may be behavioral mediators linking stress to muscle hyperreactivity and the development of facial pain. Another report suggests that excessive behavioral adjuncts develop in conjunction with fixed-time stimulus presentation. The present study assessed the extent to which the oral habits exhibited by facial pain patients are schedule-induced. Subjects with Temporomandibular Disorder (TMD) symptomatology (n = 15) and pain-free controls (n = 15) participated in a 4-phase experiment (adaptation, baseline, task, recovery) designed to elicit schedule-induced behaviors. Self-report of oral habits and negative affect were recorded after each phase. Objective measures of oral habits were obtained via behavioral observation and masseter EMG recordings. Results revealed that negative arousal significantly increased during the fixed-time (FT) task and was also associated with increased oral habits among the TMD subjects. Moreover, 40% of the TMD subjects and none of the controls exhibited a pattern of EMG elevations in the early part of the inter-stimulus interval that met a strict criteria for scheduled-induced behavior per se. Taken together, these results suggest that the TMD subjects were engaging in schedule-induced oral habits. The adjunctive behavior literature seems to provide a plausible explanation as to how oral habits develop and are maintained in TMD patients, despite their painful consequences.

Prevention of stereotypy in laboratory mice: effects on stress physiology and behaviour

According to the coping hypothesis, the adaptive significance of stereotypies in barren housing conditions may lie in their potency to attenuate the deleterious consequences of chronic stress. Present evidence from experimental studies is ambiguous. When Zur:ICR mice were selectively prevented from stereotypic wire gnawing at the cage lid, the previous amount of stereotyped behaviour after a short-term decrease in activity was compensated by variable active behaviour on the cage floor. This change in behaviour was associated with a short-term elevation of serum corticosterone concentrations 24 h after stereotypy prevention. However, 3 days later corticosterone levels were back at pretreatment base levels. Both behavioural and physiological short-term effects were caused by the impact of prevention on behavioural organization. They disappeared as soon as new habits were established, even though they were not stereotyped. In contrast to the predictions of the coping hypothesis, prevention of stereotypy had no significant effects on chronic measures of both the sympathetic-adrenal-medullary system and the hypothalamus-pituitary-adrenal system. Thus, there is no evidence that stereotypic wire gnawing reduces chronic stress in Zur:ICR mice. This implies that coping with stress is not a general aspect of cage-induced stereotypic behaviour.

Stereotypic behavior, adrenocortical function, and open field behavior of individually confined gestating sows

The adrenocortical response and open field behavior of a random sample of 37 individually confined gestating sows in different parities were tested around day 85 of pregnancy. The sows were classified as stereotyped [S] and nonstereotyped [N] based on 8-h individual behavioral observations during daytime. Behavioral analysis from time-lapse video recordings included percentage of time spent standing and sitting, as well as the duration spent performing elements of stereotyped actions. Blood samples were drawn for cortisol analysis by suborbital sinus puncture before and after adrenocortical stimulation with 200 IU ACTH. Locomotor activity in an open field, isolated visually and auditorily from other sows, was also studied. Seventeen sows exhibited stereotyped behavior for 54.9 +/- 4.8% of the 8-h observation period during daytime. The total time the sows spent standing and sitting was positively correlated with age and was significantly higher for [S] sows than for [N] sows. Sows in the [S] group exhibited a higher adrenocortical response to ACTH stimulation than [N] sows. Mean locomotor scores in the open field were higher for [S] than for [N] sows but these did not correlate with the physical activity and adrenocortical function in the home crate. Our results provide no evidence that the performance of stereotypies constitutes a mechanism that helps sows to cope in an environment of low complexity.