Evaluating pharmacological models of high and low anxiety in sheep

Sex impacts pain behaviour but not emotional reactivity of lambs following ring tail docking

Studies in humans have shown sex differences in response to painful events, however, little is known in relation to sex differences in sheep. Understanding sex differences would enable improved experimental design and interpretation of studies of painful procedures in sheep. To examine sex differences in response to pain, 80 lambs were tested across five cohorts of 16. The lambs were penned in groups containing two male and two female lambs with their respective mothers. Lambs were randomly allocated from within each block to one of four treatment groups; FRing–Female lamb, ring tail docked without analgesia, MRing–Male lamb, ring tail docked without analgesia, FSham–Female lamb, tail manipulated and MSham–Male lamb, tail manipulated. Following treatment, lambs were returned to their pen and were video recorded for 45 mins for behavioural observations of acute pain and posture. An hour after treatment, lambs then underwent an emotional reactivity test that consisted of three phases: Isolation, Novelty and Startle. Following treatment, Ring lambs displayed more abnormal postures (mean = 2.5 ± 0.5) compared to Sham lambs (mean = 0.05 ± 0.4, P = 0.0001). There was an effect of sex on the display of acute pain-related behaviours in lambs that were tail docked (P < 0.001), with female lambs displaying more acute behaviours (mean count = +2.2). This difference in behaviour between sexes was not observed in Sham lambs. There was no effect of sex on display of postures related to pain (P = 0.99). During the Novelty and Startle phase of the emotional reactivity test, Ring lambs tended to (P = 0.084) or did (P = 0.018) show more fear related behaviours, respectively. However, no effect of sex was observed. The results of this study indicate that a pain state may alter the emotional response of lambs to novel objects and potential fearful situations. It was also demonstrated that female lambs display increased sensitivity to the acute pain caused by tail docking compared to males.

Positive Aspects of Welfare in Sheep: Current Debates and Future Opportunities

The concept of positive welfare is an expansion of the traditional understanding that animal welfare is defined by minimizing stress, pain, suffering, and disease. Positive welfare shifts the animal welfare narrative from a focus on reducing negative experiences to proactively providing animals with opportunities to have positive experiences and feelings. The concept, although around for several decades, is in its infancy in terms of developing ways of assessing positive welfare on farms, especially in extensive systems, and there are challenges in the adoption of positive welfare practices and the monitoring of continuous improvement at the farm level. Using an iterative approach, this critical review aims to explore the extent to which positive welfare interventions and indicators are positioned and have been developed within the animal welfare literature for sheep. This paper critiques existing positive welfare indicators, such as choices in food and the physical environment, conspecific social synchronization, maternal bonds, intergenerational knowledge transfer, positive human-animal relationships, etc., as currently assessed by the 'good life framework'. It also reviews the characteristics of scientific measures for (positive) affective states in the current sheep literature and their potential contribution to understanding positive welfare states in sheep. In conclusion, this paper provides recommendations for future research regarding sheep welfare.

Behavioural reactivity testing in sheep indicates the presence of multiple temperament traits

Temperament in sheep is commonly presented as unidimensional, with a 'nervous' temperament indicative of fear and reactivity towards humans and novel environments. However, temperament is multidimensional, with some traits expressed only under certain conditions (context-specific). There is evidence that a common temperament test in sheep, the isolation-box (IB), measures level of activity and not fearfulness as intended, and that behaviours measured in the IB test are indicative of different traits. To investigate this, 16 behavioural responses to a human, to being startled, and to confinement (IB test) were measured in 89 lambs, twice, three months apart. Our results agree with previous studies that vocalisations in all tests and locomotion in two, show high repeatability over time. A principal component analysis identified that vocalisations are domain-general, and are indicative of the trait 'sociability', however locomotion is context-specific' and captures the traits 'exploration-avoidance', 'boldness-shyness' and 'general activity'. A cluster analysis identified four behavioural profiles that indicate the trait 'boldness-shyness' captures reactivity towards humans. This suggests the IB test, which measures 'general activity', is unsuitable for measuring reactivity towards humans in sheep, and that when studying the impact of temperament on other factors, multiple conditions should be used when identify temperament traits.

Using Real-Time Kinematic (RTK) Devices to Show a Limited Effect of Boldness and Fearfulness on Social Proximity in Sheep Grazing at Pasture

Sheep are gregarious animals that can form close inter-individual relationships. Social bonds are affected by environmental and within-animal factors, but there is limited understanding of individual factors that influence social relationships, in part due to the challenges of accurately measuring individual social proximity within a group. This study used geospatially precise RTK-GNSS localization devices (Real-Time-Kinematic Global Navigation Satellite System) to evaluate social proximity between individuals with different personality traits in small sheep flocks. First, unsupervised clustering algorithms were used to categorize 78 individual Merino sheep (from a research flock of 108 grazed together for 11 months prior) based on their behavior measured in four behavioral tests: arena, novel object, flight speed, and isolation box. Sixty-five sheep were then categorized into five cohorts of 13 individuals each (clustered into three bold, six bold/fearful, and four fearful animals per cohort). Bold/fearful animals were bold toward a novel object but fearful of a human. Sheep within a single cohort were released into a 0.70 Ha test paddock with RTK-GNSS devices attached to their backs for 3 days to monitor relative positions. All cohorts were tested sequentially over a 5-week period. Social network analyses of GNSS locational data with a distance threshold of up to 30 m for all cohorts together showed no significant effect of personality traits (P = 0.11). There were, however, some significant but inconsistent differences in distances based on personality traits within separate cohorts [i.e., cohorts 1, 3, 4 (P ≤ 0.02), cohorts 2, 5 (P ≥ 0.44)]. When GNSS locational data were analyzed with a distance threshold of up to 2 m (day 2 excluded from all cohorts due to missing values), there was a significant effect of personality traits (P = 0.01) across all cohorts combined. The bold animals showed greater distances from each other relative to their distances from fearful or bold/fearful individuals. Additionally, regardless of personality traits, the average distance between animals decreased 2.2 m over the 3 test days. Social interactions in sheep flocks may be influenced by personality traits of fearfulness and boldness, but further research with larger numbers of sheep across varying environments is needed.

Attention Bias Test Measures Negative But Not Positive Affect in Sheep: A Replication Study

Simple Summary

Attention bias tests may provide a practical measure of emotional states in livestock. An attention bias test has been developed as a measure of negative emotional states in sheep. This study aimed to determine whether the test could also be used to assess positive emotional states. Our results indicated that the attention bias test was unable to differentiate control animals from those in drug-induced positive states (p > 0.05). However, our findings further supported the suggestion that the attention bias test may measure negative emotional states in sheep. With further refinement, the attention bias test may be a useful tool to assess and improve livestock welfare.

Abstract

An attention bias test has been developed as a measure of negative affective states in sheep. The test measures an individual’s allocation of attention between a threatening (previous location of a dog) and positive (conspecific photo) stimulus over a 3 min period. This study replicated a previously inconclusive study, to determine whether the test could assess positive affective states under more controlled conditions and with a younger population of animals. Pharmacological treatments were used to induce anxious, calm, happy, and control affective states prior to entering the attention bias test arena (n = 20/treatment). We hypothesized that sheep in positive and negative affective states could be differentiated using key measures of attention during testing, including vigilance (head at or above shoulder height) and duration looking towards the valenced stimuli. Anxious sheep were more vigilant than control animals during attention bias testing as predicted (linear mixed effects model, p = 0.002), but the positive groups did not differ from controls (p > 0.05). There was no effect of treatment on looking behaviors (p > 0.05). We suggest this attention bias test paradigm can assess negative but not positive affect in sheep and that modifications to the ethogram or stimuli are needed to more clearly characterize the direction of attention during testing.

Welfare-improving enrichments greatly reduce hens' startle responses, despite little change in judgment bias

Responses to ambiguous and aversive stimuli (e.g. via tests of judgment bias and measures of startle amplitude) can indicate mammals' affective states. We hypothesised that such findings generalize to birds, and that these two responses co-vary (since both involve stimulus evaluation). To validate startle reflexes (involuntary responses to sudden aversive stimuli) and responses in a judgment bias task as indicators of avian affective state, we differentially housed hens with or without preferred enrichments assumed to improve mood (in a crossover design). To control for personality, we first measured hens' baseline exploration levels. To infer judgment bias, control and enriched hens were trained to discriminate between white and dark grey cues (associated with reward and punishment, respectively), and then probed with intermediate shades of grey. For startle reflexes, forceplates assessed responses to a light flash. Judgment bias was only partially validated: Exploratory hens showed more 'optimism' when enriched, but Non-exploratory hens did not. Across all birds, however, startle amplitudes were dramatically reduced by enrichment (albeit more strongly in Exploratory subjects): the first evidence that avian startle is affectively modulated. Startle and judgment biases did not co-vary, suggesting different underlying mechanisms. Of the two measures, startle reflexes thus seem most sensitive to avian affective state.

Pharmacologically-induced stress has minimal impact on judgement and attention biases in sheep

The emotional impact of exposure to stressors has not been well quantified in animals. We hypothesised that exogenous induction of stress in sheep would induce a pessimistic judgement bias and increased attention towards a threatening stimulus, suggestive of a negative emotional state. Stress was induced pharmacologically by administering synthetic adrenocorticotropic hormone. Judgement bias was assessed using a spatial go/no-go task after exposure to acute stress (one injection), chronic stress (21 daily injections) and acute-on-chronic stress (2 min isolation after 28 daily injections). Attention bias was assessed during chronic stress only (22 daily injections). In contrast with our hypotheses, there was no strong evidence that Synacthen administration altered judgement bias or attention bias at any stage of the experiment. Stressed sheep were more likely to approach ambiguous locations than saline Control animals, however, statistical evidence for models fitting treatment group was very weak. Overall, our findings suggest that elevated levels of cortisol may not fully explain changes to judgement bias observed in previous studies after environmentally-induced stress. Further studies are required to better understand which aspects of environmentally-induced stress alter judgement bias and to further validate cognitive methods of assessing affect in sheep.

The influence of pharmacologically-induced affective states on attention bias in sheep

When an individual attends to certain types of information more than others, the behavior is termed an attention bias. The occurrence of attention biases in humans and animals can depend on their affective states. Based on evidence from the human literature and prior studies in sheep, we hypothesized that an attention bias test could discriminate between pharmacologically-induced positive and negative affective states in sheep. The test measured allocation of attention between a threat and a positive stimulus using key measures of looking time and vigilance. Eighty 7-year-old Merino ewes were allocated to one of four treatment groups; Anxious (m-chlorophenylpiperazine), Calm (diazepam), Happy (morphine) and Control (saline). Drugs were administered 30 min prior to attention bias testing. The test was conducted in a 4 × 4.2 m arena with high opaque walls. An approximately life-size photograph of a sheep was positioned on one wall of the arena (positive stimulus). A small window with a retractable opaque cover was positioned on the opposite wall, behind which a dog was standing quietly (threat). The dog was visible for 3 s after a single sheep entered the arena, then the window was covered and the dog was removed. Sheep then remained in the arena for 3 min while behaviors were recorded. Key behaviors included time looking toward the dog wall or photo wall, duration of vigilance behavior and latency to become non-vigilant. In contrast with our hypothesis, no significant differences were found between treatment groups for duration of vigilance or looking behaviors, although Anxious sheep tended to be more vigilant than Control animals (P < 0.1) and had a longer latency to become non-vigilant (P < 0.001). A total of 24 of 80 animals were vigilant for the entire test duration. This censoring of data may explain why no differences were detected between groups for vigilance duration. Overall, a lack of difference between groups may suggest the test cannot discriminate positive and negative states in sheep. We suggest that the censoring of vigilance duration data, the use of insufficient drug doses, the potential influence of background noise and the age of the sheep may explain a lack of difference between groups. Due to these potential effects, it remains unclear whether the attention bias test can detect positive states in sheep.

Attention Bias Test Differentiates Anxiety and Depression in Sheep

Negative affective states such as anxiety and depression pose a risk to animal welfare, however, practical tests for assessing these states in animals are limited. In humans, anxious individuals are shown to pay more attention toward threatening information than non-anxious individuals, known as an attention bias. Previously, an attention bias test was developed and validated as a measure of anxious states in sheep, where more anxious sheep showed increased attention toward a threat (dog) and were more vigilant than Control animals. Studies in humans suggest that attention biases also occur in depressed individuals, with observations of attention biases toward threats, as well as biases away from positive stimuli. Given these findings, we hypothesized that an attention bias test for sheep could also be used to assess states of depression. We predicted that Merino ewes in pharmacologically induced Depressed (para-chlorophenylalanine) and Anxious (m-chlorophenylpiperazine) states would show greater attention toward a threat than Control animals (saline), but that the Depressed sheep would show relatively less interest in a positive stimulus (photograph of a conspecific). During testing, Depressed sheep paid more attention toward the threat and less toward the photograph than Control animals as predicted (Analyses of Variance, P < 0.05, n = 16 per treatment). Interestingly, Anxious sheep showed an attention bias in the opposite direction, paying more attention toward the photograph and less toward the threat than Control animals (P < 0.05). Both Anxious and Depressed sheep were more vigilant than Control animals (P = 0.002). These results suggest the attention bias test can be used to measure and differentiate states of depression and anxiety in livestock. The bidirectional nature of the attention bias identified between treatments highlights the importance of measuring multiple behaviors in the test and considering the context in which the test is applied. This will enable a clearer characterization of the affective state of an animal, as an aspect of its welfare.

Towards a more practical attention bias test to assess affective state in sheep

Tests for attention bias potentially offer more rapid assessment of affective state in animals than existing cognitive methods. An attention bias test has previously been developed for sheep and validated as a measure of anxious states. The 3 minute test assessed behavioural responses of sheep in an enclosed arena after brief exposure to the threat of a dog. Experiment 1 of the current study aimed to refine the previously developed method, removing the need for a habituation period and shortening the test duration. Sheep were given either an anxiolytic drug, an anxiogenic drug or a control treatment prior to testing to induce contrasting affective states. Differences in behaviour were found between the treatment groups within the first 45s of the test, indicating the original test duration could be shortened from 180 s. During testing, 36 of 40 animals in the control and anxiolytic groups ate the novel feed offered in the test, indicating it is not necessary to habituate animals to a feed container. Experiment 2 aimed to confirm the responses measured in the test were primarily towards the dog rather than other aspects of the test environment. Sheep exposed to an empty window at the beginning of the test behaved differently to those which were exposed to a dog, indicating sheep behaviour in the test is at least partially a response to the dog. A third group of sheep were also tested with the dog immediately after having small data loggers attached to their necks. Behaviour of these sheep did not differ from the sheep tested without loggers, indicating data logger attachment did not impact their behaviour in the test. In both experiments, treatments did not appear to modify activity (zones crossed), which we propose indicates the test was primarily detecting valence of the affective state rather than arousal.

Attention bias to threat indicates anxiety differences in sheep

Humans and animals show increased attention towards threatening stimuli when they are in increased states of anxiety. The few animal studies that have examined this phenomenon, known as attention bias, have applied environmental manipulations to induce anxiety but the effects of drug-induced anxiety levels on attention bias have not been demonstrated. Here, we present an attention bias test to identify high and low anxiety states in sheep using pharmacological manipulation. Increased anxiety was induced using 1-methyl-chlorophenylpiperazine (m-CPP) and decreased anxiety with diazepam, and then we examined the behaviour of sheep in response to the presence of a dog as a threat. Increased attention towards the threat and increased vigilance were shown in sheep that received the m-CPP and reduced in sheep receiving the diazepam. The modulated attention towards a threat displayed by the m-CPP and diazepam animals suggests that attention bias can assess different levels of anxiety in sheep. Measuring attention bias has the potential to improve animal welfare assessment protocols.

Potential Emergence of Multi-quorum Sensing Inhibitor Resistant (MQSIR) Bacteria

Expression of certain bacterial genes only at a high bacterial cell density is termed as quorum-sensing (QS). Here bacteria use signaling molecules to communicate among themselves. QS mediated genes are generally involved in the expression of phenotypes such as bioluminescence, biofilm formation, competence, nodulation, and virulence. QS systems (QSS) vary from a single in Vibrio spp. to multiple in Pseudomonas and Sinorhizobium species. The complexity of QSS is further enhanced by the multiplicity of signals: (1) peptides, (2) acyl-homoserine lactones, (3) diketopiperazines. To counteract this pathogenic behaviour, a wide range of bioactive molecules acting as QS inhibitors (QSIs) have been elucidated. Unlike antibiotics, QSIs don't kill bacteria and act at much lower concentration than those of antibiotics. Bacterial ability to evolve resistance against multiple drugs has cautioned researchers to develop QSIs which may not generate undue pressure on bacteria to develop resistance against them. In this paper, we have discussed the implications of the diversity and multiplicity of QSS, in acting as an arsenal to withstand attack from QSIs and may use these as reservoirs to develop multi-QSI resistance.