Investigating anhedonia in a non-conventional species: Do some riding horses Equus caballus display symptoms of depression?

International audienceInvestigating depression-like conditions in animals is methodologically challenging, but potentially important for welfare. Some riding horses display ‘withdrawn’ states of inactivity and low responsiveness that resemble the reduced engagement with the environment shown by certain depressed patients. To assess whether these animals are experiencing a depression-like state, we investigated anhedonia – the loss of pleasure, a key symptom of human depression – in 20 withdrawn and non-withdrawn horses from the same stable. The time horses spent being withdrawn appeared unrelated to age or sex, but correlated with time devoted to stereotypic behaviour, a possible marker of lifetime stress. Comparison with data collected 5 years earlier also revealed that horses scored as withdrawn then remained significantly likely to display the behaviour. We measured sucrose intake, a classic measure of anhedonia never previously applied to horses. Flavoured sugar blocks, novel to these subjects, were mounted in each stall and weighed 3, 8, 24 and 30 h after provision. We predicted that if affected by depression-like states, the most withdrawn horses would consume the least sucrose. This prediction was met (F1,18 = 4.65, two tailed p = 0.04). This pattern could, however, potentially reflect general appetite levels and/or food neophobia. To control for these confounds, hay consumption was measured over 5 days, as were subjects’ latencies to eat a meal scented with a novel odour. Although low hay consumption and long latencies to eat scented food did predict low sucrose consumption, statistically controlling for these confounds did not eliminate the relationship between being withdrawn and consuming less sucrose (although reducing it to a strong trend): F1,15 = 4.28, two-tailed p = 0.056. These data thus suggest long-lasting depression-like states in certain riding horses, which correlate with stereotypic behaviour and are characterised by anhedonia and bouts of ‘withdrawn’ unresponsiveness

Do potentially depressed horses lack attention? A differential temporal pattern of responses towards auditory stimuli

International audienceA recent study described an inactive state in domestic horses, termed withdrawn hereafter and characterised by an atypical posture and low responsiveness to tactile and environmental stimuli. Aiming at determining the potential role of underlying depression in this state, we investigated whether the attentional state, frequently impaired in depressed patients, differ between withdrawn horses (n = 12) and control non-withdrawn animals from the same stable (n = 15). These 27 horses (5 mares, 22 geldings, French Saddlebred, 4-20 years old) were exposed once a day for 5 consecutive days to a novel auditory stimulus, broadcasted for 3 seconds in horses’ home environment. We recorded standard measures of attentional state (e.g. time spent with ears, head and/or neck orientated towards the loudspeaker). Different temporal patterns of attentional responses appeared: withdrawn horses paid less attention to stimuli on the first day (Wilcoxon, p0.05). Moreover, time focused on the loudspeaker was lower in withdrawn than in control horses on this first day (Mann-Whitney, p<0.05). Withdrawn horses therefore seem to “switch off” from environmental stimuli compared to control horses, which might reflect lack of attention

L’état de bien-être/mal-être du cheval : un facteur de modulation de l’attention ?

National audienceL’identification de critères permettant de caractériser de façon fiable l’état de bien-être chez le cheval apparaît aujourd’hui encore comme une question cruciale. L’identification de paramètres sanitaires (e.g. condition physique) et physiologiques (e.g. rythme cardiaque) apparaissent être les mesures les plus communément utilisées. Cependant, certains troubles peuvent être difficiles à évaluer, notamment l’état interne des animaux (bien-être mental). Les chevaux domestiques peuvent être soumis à un stress chronique, qui, chez l’homme, conduit à une variété d’effets psychologiques négatifs. Une étude récente (Fureix et al, 2012) a décrit un état inactif chez des chevaux domestiques, appelée ci-après « figé » et caractérisé par une posture atypique (i.e. poids vers l’avant main, horizontalité globale) ainsi qu’une fixité du regard, de la tête, de l’encolure, voire des oreilles suggérant un retrait de ces individus par rapport à leur environnement. Des tests ont révélé de surcroit une faible réactivité à des stimuli tactiles et humains. Il a été proposé que ces « syndromes » correspondaient à un état « dépressif » qui chez l’homme se traduit aussi par des déficits attentionnels et un désintérêt par rapport aux stimuli de l’environnement. Afin de tester l’attention des chevaux figés et non figés envers des stimuli de l’environnement, nous avons soumis 12 chevaux figés et 15 chevaux non figés vivant dans la même écurie (centre équestre) à des tests expérimentaux utilisant des stimuli auditifs. Ces 27 chevaux (5 juments, 22 hongres, de race Selle Français, âgés de 4 à 20 ans) ont été exposés une fois par jour pendant 5 jours consécutifs à un stimulus auditif nouveau, diffusé pendant 3 secondes dans le milieu habituel des chevaux (i.e. au box). Nous avons enregistré des mesures classiques de l'état attentionnel (e.g. temps passé avec les oreilles, la tête et / ou l’encolure orientés vers le haut-parleur). Différents pattern temporels de réponses attentionnelles sont apparus: le premier jour de diffusion les chevaux figés étaient moins attentifs aux stimuli que les autres jours (Test de Wilcoxon, p 0,05). De plus, le temps passé attentif vers le stimulus auditif était plus faible pour les chevaux figés que pour les chevaux non figés dès le 1er jour (Test de Mann-Whitney, p <0,05). Les chevaux figés semblent donc être « coupés » des stimuli environnementaux. L’ensemble des résultats suggèrent un «syndrome» chez le cheval qui rappel un état dépressif chez l'homme, faisant du cheval un modèle animal nouveau et approprié des troubles humains. Ces résultats indiquent aussi qu’une attention particulière doit être portée aux chevaux présentant cette attitude, d’autant qu’il a pu être montré qu’à ces troubles comportementaux et posturaux, s’ajoute une perturbation endocrinienne (i.e. taux de cortisol anormalement bas)

Do depressed horses lack attention? A differential temporal pattern of responses towards auditory stimuli

National audience[No abstract

Do depressed horses (Equus caballus) lack attention? A different temporal pattern of responses towards auditory stimuli

International audienceDomestic horses often encounter chronic stress, which in humans leads to a variety of negative psychological effects, including clinical depression. A recent study described an inactive state in domestic horses, termed withdrawn hereafter and characterised by an atypical posture, states of inactivity and low responsiveness to external stimuli, which resemble the reduced engagement with the environment seen in depressed patients. To assess whether these horses are affected by a depression-like condition, we investigated whether attentional abilities, frequently impaired in depressed patients, differ between withdrawn horses (n=12; 3 mares, 9 geldings, 20-6 and 13±1 mean years old) and control non-withdrawn animals from the same stable (n=15; 2 mares, 13 geldings, 18-4 and 10±1 mean years old), all French Saddlebred. These horses were exposed once a day for 5 consecutive days to a novel auditory stimulus, broadcasted for 3 seconds in horses’ home environment. We recorded standard measures of attentional state (e.g. time spent with ears, head and/or neck orientated towards the loudspeaker). Different temporal patterns of attentional responses appeared: withdrawn horses spent less time focused on the loudspeaker on the first day (Wilcoxon, P0.05). Moreover, time focused on the loudspeaker was lower in withdrawn than in control horses on this first day (Mann-Whitney, P<0.05). Withdrawn horses therefore seem to ‘switch off ’ from environmental stimuli compared to control horses on the first trial, which might reflect lack of attention. Altogether, with a recent study revealing anhedonia (a core symptom of clinical depression) in withdrawn horses, results suggest a ‘syndrome’ that resemble clinical depression in humans, and open a promising line of investigation of what altered welfare states could look like in horses

Investigating anhedonia in a non-conventional species : are some riding horses depressed?

International audienceSome riding horses display states of inactivity and low responsiveness to external stimuli that we term ‘withdrawn’, and that resemble the reduced engagement with the environment seen in clinically depressed people. To assess whether these animals are indeed affected by a depression-like condition, we investigated anhedonia: the loss of pleasure that is a core symptom of human clinical depression. Subjects were withdrawn horses and controls from the same stable (16 geldings and 4 mares, 7-20 years old, 85% French Saddlebred). The time individuals spent being withdrawn was determined by a trained observer using instantaneous scan sampling every 2 minutes over 1 h long periods repeated daily over 15 days. To measure sucrose intake, a classic measure of anhedonia in rodent-based biomedical research never previously applied to horses, commercially-available flavoured sugar blocks, novel to these subjects, were mounted in each stall and weighed 3, , 24 and 30 h after provision. We hypothesized that if depressed-like, withdrawn horses would consume less sucrose than controls. Horses spending the most time withdrawn did show reduced sucrose consumption (F1,18=4.65, P=0.04, in a repeated measures model also controlling for age, sex, and the time each horse spent in its stall – thus able to eat the sucrose – during testing). We then controlled for two possible alternative explanations for this pattern: neophobia towards novel foods, and generally low appetites. Hay consumption was measured over 5 days, as were subjects’ latencies to eat a meal scented with a novel odour. When included in our model, high hay consumption strongly tended to predict high sucrose consumption (F1,14=4.52, P=0.051), while long latencies to eat a novel food predicted low sucrose consumption (F1,14=8.34, P=0.012). However, statistically controlling for these two confounds did not eliminate the relationship between being withdrawn and consuming less sucrose (although reducing it to a strong trend: F1,15=4.28, P=0.056), suggesting that neither overall food consumption levels nor neophobic reactions explained our previous findings. Overall, this study illustrates the methodological challenges of investigating anhedonia in non-conventional species; reveals possible depression-like conditions in riding horses; and suggests a way of assess anhedonia in other animals showing profound inactivity (e.g. working equids in the developing world)