Describing certain animal behaviours as ‘depression-like’ or ‘depressive’ has become common across several fields of research. These typically involve unusually low activity or unresponsiveness and/or reduced interest in pleasure (anhedonia). While the term ‘depression-like’ carefully avoids directly claiming that animals are depressed, this narrative review asks whether stronger conclusions can be legitimate, with animals developing the clinical disorder as seen in humans (cf., DSM-V/ICD-10). Here, we examine evidence from animal models of depression (especially chronically stressed rats) and animals experiencing poor welfare in conventional captive conditions (e.g., laboratory mice and production pigs in barren environments). We find troubling evidence that animals are indeed capable of experiencing clinical depression, but demonstrate that a true diagnosis has yet to be confirmed in any case. We thus highlight the importance of investigating the co-occurrence of depressive criteria and discuss the potential welfare and ethical implications of animal depression.
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Abramson, L.Y., Seligman, M.E. & Teasdale, J.D. (1978). Learned helplessness in humans: critique and reformulation. — J. Abnorm. Psychol. 87: 49-74.
Acklin, C.J. & Gault, R.A. (2015). Effects of natural enrichment materials on stress, memory and exporatory behaivour in mice. — Lab Anim. 7: 262-267.
Adcock, S.J.J. & Tucker, C.B. (2020). Conditioned place preference reveals ongoing pain in calves 3 weeks after disbudding. — Sci. Rep. 10: 3849.
Adcock, S.J.J., Cruz, D.M. & Tucker, C.B. (2020). Behavioral changes in calves 11 days after cautery disbudding: effect of local anesthesia. — J. Dairy Sci. 103: 8518-8525.
Alò, R., Mele, M., Avolio, E., Fazzari, G. & Canonaco, M. (2015). Distinct amygdalar AMPAergic/GABAergic mechanisms promote anxiolitic-like effects in an unpredictable stress model of the hamster. — J. Mol. Neurosci. 55: 541-551.
American Psychiatric Association (2013). Diagnostic and statistical manual of mental disorders, 5th edn. — American Psychiatric Association, Arlington, VA.
Antoniuk, S., Bijata, M., Ponimaskin, E. & Wlodarczyk, J. (2019). Chronic unpredictable mild stress for modeling depression in rodents: meta-analysis of model reliability. — Neurosci. Biobehav. Rev. 99: 101-116.
Armstrong, E.A., Rufener, C., Toscano, M.J., Eastham, J.E., Guy, J.H., Sandilands, V., Boswell, T. & Smulders, T.V. (2020). Keel bone fractures induce a depressive-like state in laying hens. — Sci. Rep. 10: 3007.
Ashkenazy-Frolinger, T., Einat, H. & Kronfeld-Schor, N. (2015). Diurnal rodents as an advantageous model for affective disorders: novel data from diurnal degu (Octodon degus). — J. Neural Transm. 122: 35-45.
Ayensu, W.K., Pucilowski, O., Mason, G.A., Overstreet, D.H., Rezvani, A.H. & Janowsky, D.S. (1995). Effects of chronic mild stress on serum complement activity, saccharin preference, and corticosterone levels in Flinders lines of rats. — Physiol. Behav. 57: 165-169.
Bachmann, I., Audigé, L. & Stauffacher, M. (2003). Risk factors associated with behavioural disorders of crib-biting, weaving and box-walking in Swiss horses. — Equine Vet. J. 35: 158-163.
Bair, M.J., Robinson, R.L., Katon, W. & Kroenke, K. (2003). Depression and pain comorbidity. — Arch. Intern. Med. 163: 2433-2455.
Balcombe, J.P. (2006). Laboratory environments and rodents’ behavioural needs: a review. — Lab. Anim. 40: 217-235.
Baldwin, D.S. (2001). Depression and sexual dysfunction. — Br. Med. Bull. 57: 81-99.
Barret, M.S. & Barber, J.P. (2007). Interpersonal profiles in major depressive disorder. — J. Clin. Psychol. 63: 247-266.
Bates, A.J., Eder, P. & Laven, R.A. (2015). Effect of analgesia and anti-inflammatory treatment on weight gain and milk intake of dairy calves after disbudding. — N. Z. Vet. J. 63: 153-157.
Beattie, V.E., O’Connell, N.E., Kilpatrick, D.J. & Moss, B.W. (2000). Influence of environmental enrichment on welfare-related behavioural and physiological parameters in growing pigs. — Anim. Sci. 70: 443-450.
Bekris, S., Antoniou, K., Daskas, S. & Papadopoulou-Daifoti, Z. (2005). Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains. — Behav. Brain Res. 161: 45-59.
Benaroya-Milshtein, N., Hollander, N., Apter, A., Kukulansky, T., Raz, N., Wilf, A., Yaniv, I. & Pick, C.G. (2004). Environmental enrichment in mice decreases anxiety, attenuates stress responses and enhances natural killer cell activity. — Eur. J. Neurosci. 20: 1341-1347.
Bethell, E.J. (2015). A “how-to” guide for designing judgment bias studies to assess captive animal welfare. — J. Appl. Anim. Welf. Sci. 18: S18-S42.
Bielajew, C., Konkle, A.T.M. & Merali, Z. (2002). The effects of chronic mild stress on male Sprague-Dawley and Long Evans rats: I. Biochemical and physiological analyses. — Behav. Brain Res. 136: 583-592.
Bifulco, A., Bernazzani, O., Moran, P.M. & Ball, C. (2000). Lifetime stressors and recurrent depression: preliminary findings of the adult life phase interview (ALPHI). — Soc. Psychiatry Psychiatr. Epidemiol. 35: 264-275.
Biomarkers Definitions Working Group (2001). Biomarkers and surrogate endpoints: preferred definitions and conceptual framework. — Clin. Pharmacol. Ther. 69: 89-95.
Blaine, B. (2008). Does depression cause obesity?: a meta-analysis of longitudinal studies of depression and weight control. — J. Health Psychol. 13: 1190-1197.
Bora, E. & Berk, M. (2016). Theory of mind in major depressive disorder: a meta-analysis. — J. Affect. Disord. 191: 49-55.
Bortolato, M., Mangieri, R.A., Fu, J., Kim, J.H., Arguello, O., Duranti, A., Tontini, A., Mor, M., Tarzia, G. & Piomelli, D. (2007). Antidepressant-like activity of the fatty acid amide hydrolase inhibitor URB597 in a rat model of chronic mild stress. — Biol. Psychiatry 62: 1103-1110.
Bourjade, M., Moulinot, M., Henry, S., Richard-Yris, M.A. & Hausberger, M. (2008). Could adults be used to improve social skills of young horses, Equus caballus? — Dev. Psychobiol. 50: 408-417.
Bracke, M.B.M., Metz, J.H.M., Spruijt, B.M. & Scheuten, W.G.P. (2002a). Decision support system for overall welfare assessment in pregnant sows B: validation by expert opinion. — J. Anim. Sci. 80: 1835-1845.
Bracke, M.B.M., Spruijt, B.M., Metz, J.H.M. & Scheuten, W.G.P. (2002b). Decision support system for overall welfare assessment in pregnant sows A: model structure and weighting procedure. — J. Anim. Sci. 80: 1819-1834.
Brown, L.F., Kroenke, K., Theobald, D.E., Wu, J. & Tu, W. (2010). The association of depression and anxiety with health-related quality of life in cancer patients with depression and/or pain. — Psychooncology 19: 734-741.
Brunoni, A.R., Lopes, M. & Fregni, F. (2008). A systematic review and meta-analysis of clinical studies on major depression and BDNF levels: implications for the role of neuroplasticity in depression. — Int. J. Neuropsychopharmacol. 11: 1169-1180.
Burman, O.H.P., Parker, R., Paul, E.S. & Mendl, M. (2008). A spatial judgement task to determine background emotional state in laboratory rats, Rattus norvegicus. — Anim. Behav. 76: 801-809.
Burn, C.C., Dennison, T.L. & Whay, H.R. (2010). Relationships between behaviour and health in working horses, donkeys, and mules in developing countries. — Appl. Anim. Behav. Sci. 126: 109-118.
Burton, C., McKinstry, B., Tǎtar, A.S., Serrano-Blanco, A., Pagliari, C. & Wolters, M. (2013). Activity monitoring in patients with depression: a systematic review. — J. Affect. Disord. 145: 21-28.
Buyukdura, J.S., McClintock, S.M. & Croarkin, P.E. (2011). Psychomotor retardation in depression: biological underpinnings, measurement, and treatment. — Progr. Neuro-Psychopharmacol. Biol. Psychiatr. 35: 395-409.
Camus, S.M.J., Blois-Heulin, C., Li, Q., Hausberger, M. & Bezard, E. (2013). Behavioural profiles in captive-bred cynomolgus macaques: towards monkey models of mental disorders? — PLoS ONE 8: 1-14.
Camus, S.M.J., Rochais, C., Blois-Heulin, C., Li, Q., Hausberger, M. & Bezard, E. (2014). Depressive-like behavioral profiles in captive-bred single- and socially-housed rhesus and cynomolgus macaques: a species comparison. — Front. Behav. Neurosci. 8: 1-15.
Canadian Council on Animal Care (2021). CCAC guidelines: animal welfare assessment. — Canadian Council on Animal Care, Ottawa, ON.
Casey-Trott, T.M. & Widowski, T.M. (2016). Behavioral differences of laying hens with fractured keel bones within furnished cages. — Front. Vet. Sci. 3: https://doi.org/10.3389/fvets.2016.00042.
Castagné, V., Moser, P., Roux, S. & Porsolt, R.D. (2011). Rodent models of depression: forced swim and tail suspension behavioral despair tests in rats and mice. — Curr. Protocol. Neurosci.: 1-14.
Chaby, L.E., Cavigelli, S.A., White, A., Wang, K. & Braithwaite, V.A. (2013). Long-term changes in cognitive bias and coping response as a result of chronic unpredictable stress during adolescence. — Front. Hum. Neurosci. 7: 1-10.
Chachamovich, E., Fleck, M., Laidlaw, K. & Power, M. (2008). Impact of major depression and subsyndromal symptoms on quality of life and attitudes toward aging in an international sample of older adults. — Gerontologist 48: 593-602.
Cheeta, S., Ruigt, G., Van Proosdij, J. & Willner, P. (1997). Changes in sleep architecture following chronic mild stress. — Biol. Psychiatr. 41: 419-427.
Chen, C., Wang, L., Rong, X., Wang, W. & Wang, X. (2015). Effects of fluoxetine on protein expression of potassium ion channels in the brain of chronic mild stress rats. — Acta Pharm. Sin. B 5: 55-61.
Chourbaji, S., Zacher, C., Sanchis-Segura, C., Spanagel, R. & Gass, P. (2005). Social and structural housing conditions influence the development of a depressive-like phenotype in the learned helplessness paradigm in male mice. — Behav. Brain Res. 164: 100-106.
Clemenson, G.D., Deng, W. & Gage, F.H. (2015). Environmental enrichment and neurogenesis: from mice to humans. — Curr. Opin. Behav. Sci. 4: 56-62.
Clubb, R. & Mason, G. (2002). A review of the welfare of zoo elephants a review of the welfare of zoo elephants in Europe, a report commissioned by the RSPCA. — RSPCA, Horsham.
Commons, K.G., Cholanians, A.B., Babb, J.A. & Ehlinger, D.G. (2017). The rodent forced swim test measures stress-coping strategy, not depression-like behavior. — ACS Chem. Neurosci. 8: 955-960.
Cooper, J.J., McDonald, L. & Mills, D.S. (2000). The effect of increasing visual horizons on stereotypic weaving: implications for the social housing of stabled horses. — Appl. Anim. Behav. Sci. 69: 67-83.
Council of the European Union (2001). Council Directive 2001/88/EC amending Directive 91/630/EEC laying down minimum standards for the protection of pigs. — Available online at https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32001L0088.
Cryan, J.F. & Holmes, A. (2005). Model organisms: the ascent of mouse: advances in modelling human depression and anxiety. — Nat. Rev. Drug Discov. 4: 775-790.
Cuijpers, P., De Graaf, R. & Van Dorsselaer, S. (2004). Minor depression: risk profiles, functional disability, health care use and risk of developing major depression. — J. Affect. Disord. 79: 71-79.
Czéh, B., Michaelis, T., Watanabe, T., Frahm, J., De Biurrun, G., Van Kampen, M., Bartolomucci, A. & Fuchs, E. (2001). Stress-induced changes in cerebral metabolites, hippocampal volume, and cell proliferation are prevented by antidepressant treatment with tianeptine. — Proc. Natl. Acad. Sci. USA 98: 12796-12801.
Dalla, C., Antoniou, K., Drossopoulou, G., Xagoraris, M., Kokras, N., Sfikakis, A. & Papadopoulou-Daifoti, Z. (2005). Chronic mild stress impact: are females more vulnerable? — Neuroscience 135: 703-714.
Dallagnol, K.M.C., Remor, A.P., da Silva, R.A., Prediger, R.D., Latini, A. & Aguiar, A.S. (2017). Running for REST: physical activity attenuates neuroinflammation in the hippocampus of aged mice. — Brain. Behav. Immun. 61: 31-35.
D’Aquila, P.S., Peana, A.T., Carboni, V. & Serra, G. (2000). Exploratory behaviour and grooming after repeated restraint and chronic mild stress: effect of desipramine. — Eur. J. Pharmacol. 399: 43-47.
de Jong, I.C., Prelle, I.T., Van De Burgwal, J.A., Lambooij, E., Korte, S.M., Blokhuis, H.J. & Koolhaas, J.M. (2000). Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs. — Physiol. Behav. 68: 571-578.
De Vry, J., Prickaerts, J., Jetten, M., Hulst, M., Steinbusch, H.W.M., van den Hove, D.L.A., Schuurman, T. & van der Staay, F.J. (2012). Recurrent long-lasting tethering reduces BDNF protein levels in the dorsal hippocampus and frontal cortex in pigs. — Horm. Behav. 62: 10-17.
Denver, R.J. (2009). Structural and functional evolution of vertebrate neuroendocrine stress systems. — Ann. N. Y. Acad. Sci. 1163: 1-16.
Doan, L., Manders, T. & Wang, J. (2015). Neuroplasticity underlying the comorbidity of pain and depression. — Neural Plast.: 1-16.
Douglas, C., Bateson, M., Walsh, C., Bédué, A. & Edwards, S.A. (2012). Environmental enrichment induces optimistic cognitive biases in pigs. — Appl. Anim. Behav. Sci. 139: 65-73.
Dunlop, B.W. & Davis, P.G. (2008). Combination treatment with benzodiazepines and SSRIs for comorbid anxiety and depression: a review. — Prim. Care Companion J. Clin. Psychiatr. 10: 222-228.
Duque, A. & Vázquez, C. (2015). Double attention bias for positive and negative emotional faces in clinical depression: evidence from an eye-tracking study. — J. Behav. Ther. Exp. Psychiatr. 46: 107-114.
Eckstein, S. (2012). Depression in dogs: even dogs can get the blues. Learn about symptoms and treatments for dog depression. — Available online at https://pets.webmd.com/dogs/features/depression-in-dogs#1.
Enkel, T., Gholizadeh, D., Von Bohlen Und Halbach, O., Sanchis-Segura, C., Hurlemann, R., Spanagel, R., Gass, P. & Vollmayr, B. (2010). Ambiguous-cue interpretation is biased under stress-and depression-like states in rats. — Neuropsychopharmacology 35: 1008-1015.
European Union (2007). Treaty of Lisbon amending the treaty on European Union and the treaty establishing the European Community. — European Union, Brussels.
Everaert, J., Podina, I.R. & Koster, E.H.W. (2017). A comprehensive meta-analysis of interpretation biases in depression. — Clin. Psychol. Rev. 58: 33-48.
Felger, J.C. & Miller, A.H. (2012). Cytokine effects on the basal ganglia and dopamine function: the subcortical source of inflammatory malaise. — Front. Neuroendocrinol. 33: 315-327.
Ferdowsian, H.R., Durham, D.L., Kimwele, C., Kranendonk, G., Otali, E., Akugizibwe, T., Mulcahy, J.B., Ajarova, L. & Johnson, C.M. (2011). Signs of mood and anxiety disorders in chimpanzees. — PLoS ONE 6: e19855.
Figueroa, J., Solà-Oriol, D., Manteca, X., Pérez, J.F. & Dwyer, D.M. (2015). Anhedonia in pigs? Effects of social stress and restraint stress on sucrose preference. — Physiol. Behav. 151: 509-515.
Fox, M.W. (1968). Abnormal behavior in animals. — W.B Saunders, Philedalphia, PA.
Fraser, A.F. (1988). Animal suffering: the appraisal and control of depression and distress in livestock. — Appl. Anim. Behav. Sci. 20: 127-133.
Fraser, A.F. & Quine, J.P. (1989). Veterinary examination of suffering as a behaviour-linked condition. — Appl. Anim. Behav. Sci. 23: 353-364.
Fraser, D. & Duncan, I.J.H. (1998). “Pleasures”, “pains” and animal welfare: toward a natural history of affect. — Anim. Welf. 7: 383-396.
Frazer, A. & Morilak, D.A. (2005). What should animal models of depression model? — Neurosci. Biobehav. Rev. 29: 515-523.
Fried, E.I. & Nesse, R.M. (2015). Depression is not a consistent syndrome: an investigation of unique symptom patterns in the STAR*D study. — J. Affect. Disord. 172: 96-102.
Frisbee, J.C., Brooks, S.D., Stanley, S.C. & D’Audiffret, A.C. (2015). An unpredictable chronic mild stress protocol for instigating depressive symptoms, behavioral changes and negative health outcomes in rodents. — J. Vis. Exp. 106: e53109.
Frodl, T. (2017). Recent advances in predicting responses to antidepressant treatment. — F1000Research 6: 619.
Fureix, C., Jego, P., Henry, S., Lansade, L. & Hausberger, M. (2012). Towards an ethological animal model of depression? A study on horses. — PLoS ONE 7: 1-9.
Fureix, C., Beaulieu, C., Argaud, S., Rochais, C., Quinton, M., Henry, S., Hausberger, M. & Mason, G. (2015). Investigating anhedonia in a non-conventional species: do some riding horses Equus caballus display symptoms of depression? — Appl. Anim. Behav. Sci. 162: 26-36.
Fureix, C., Walker, M., Harper, L., Reynolds, K., Saldivia-woo, A. & Mason, G. (2016). Stereotypic behaviour in standard non-enriched cages is an alternative to depression-like responses in C57BL/6 mice. — Behav. Brain Res. 305: 186-190.
Geoffroy, P.A., Hoertel, N., Etain, B., Bellivier, F., Delorme, R., Limosin, F. & Peyre, H. (2018). Insomnia and hypersomnia in major depressive episode: prevalence, sociodemographic characteristics and psychiatric comorbidity in a population-based study. — J. Affect. Disord. 226: 132-141.
Geschwind, D.H. & Flint, J. (2015). Genetics and genomics of psychiatric disease. — Science 349: 1489-1494.
Gibbons, T.E., Pence, B.D., Petr, G., Ossyra, J.M., Mach, H.C., Bhattacharya, T.K., Perez, S., Martin, S.A., McCusker, R.H., Kelley, K.W., Rhodes, J.S., Johnson, R.W. & Woods, J.A. (2014). Voluntary wheel running, but not a diet containing (–)-epigallocatechin-3-gallate and β-alanine, improves learning, memory and hippocampal neurogenesis in aged mice. — Behav. Brain Res. 272: 131-140.
Glassman, A.H. (2007). Depression and cardiovascular comorbidity. — Dialogues Clin. Neurosci. 9: 9-17.
Gold, P.W. & Chrousos, G.P. (2002). Organization of the stress system and its dysregulation in melancholic and atypical depression: high vs low CRH/NE states. — Mol. Psychiatr. 7: 254-275.
Gorka, Z., Moryl, E. & Papp, M. (1996). Effect of chronic mild stress on circadian rhythms in the locomotor activity in rats. — Pharmacol. Biochem. Behav. 54: 229-234.
Gottlieb, D.H., Capitanio, J.P. & Mccowan, B. (2013). Risk factors for stereotypic behavior and self-biting in rhesus macaques (Macaca mulatta): animal’s history, current environment, and personality. — Am. J. Primatol. 75: 995-1008.
Graf, B. & Senn, M. (1999). Behavioural and physiological responses of calves to dehorning by heat cauterization with or without local anaesthesia. — Appl. Anim. Behav. Sci. 62: 153-171.
Grippo, A.J., Beltz, T.G. & Johnson, A.K. (2003). Behavioral and cardiovascular changes in the chronic mild stress model of depression. — Physiol. Behav. 78: 703-710.
Grippo, A.J., Francis, J., Beltz, T.G., Felder, R.B. & Johnson, A.K. (2005). Neuroendocrine and cytokine profile of chronic mild stress-induced anhedonia. — Physiol. Behav. 84: 697-706.
Grønli, J., Murison, R., Bjorvatn, B., Sørensen, E., Portas, C.M. & Ursin, R. (2004). Chronic mild stress affects sucrose intake and sleep in rats. — Behav. Brain Res. 150: 139-147.
Grønli, J., Murison, R., Fiske, E., Bjorvatn, B., Sørensen, E., Portas, C.M. & Ursin, R. (2005). Effects of chronic mild stress on sexual behavior, locomotor activity and consumption of sucrose and saccharine solutions. — Physiol. Behav. 84: 571-577.
Gururajan, A., Reif, A., Cryan, J.F. & Slattery, D.A. (2019). The future of rodent models in depression research. — Nature Rev. Neurosci. 20: 686-701.
Gutwein, B.M. & Fishbein, W. (1979a). Paradoxical sleep and memory (I): selective alterations following enriched and impoverished environmental rearing. — Brain Res. Bull. 5: 9-12.
Gutwein, B.M. & Fishbein, W. (1979b). Paradoxical sleep and memory (II): sleep circadian rhythmicity following enriched and impoverished environmental rearing. — Brain Res. Bull. 5: 105-109.
Harburger, L.L., Nzerem, C.K. & Frick, K.M. (2007). Single enrichment variables differentially reduce age-related memory decline in female mice. — Behav. Neurosci. 121: 679-688.
Hardin, E., Castro, F.L.S. & Kim, W.K. (2019). Keel bone injury in laying hens: the prevalence of injuries in relation to different housing systems, implications, and potential solutions. — World Poult. Sci. J. 75: 285-291.
Harding, E.J., Paul, E.S. & Mendl, M. (2004). Cognitive bias and affective state. — Nature 427: 312.
Harkness, K.L., Bruce, A.E. & Lumley, M.N. (2006). The role of childhood abuse and neglect in the sensitization to stressful life events in adolescent depression. — J. Abnorm. Psychol. 115: 730-741.
Harlander-Matauschek, A., Rodenburg, T.B., Sandilands, V., Tobalske, B.W. & Toscano, M.J. (2015). Causes of keel bone damage and their solutions in laying hens. — Worlds. Poult. Sci. J. 71: 461-472.
Harvey, N.D., Moesta, A., Kappel, S., Wongsaengchan, C., Harris, H., Craigon, P.J. & Fureix, C. (2019). Could greater time spent displaying waking inactivity in the home environment be a marker for a depression-like state in the domestic dog? — Animals 9.
Harvey, N.D., Moesta, A., Wongsaengchan, C., Harris, H., Craigon, P.J. & Fureix, C. (2020). Investigating putative depression-like states in the domestic dog: does greater time spent displaying waking inactivity in the home kennel co-vary with negative judgment of ambiguity? — Appl. Anim. Behav. Sci. 230: 105025.
Hausberger, M., Gautier, E., Biquand, V., Lunel, C. & Jégo, P. (2009). Could work be a source of behavioural disorders? A study in horses. — PLoS ONE 4: e7625.
Heinrich, A., Duffield, T.F., Lissemore, K.D. & Millman, S.T. (2010). The effect of meloxicam on behavior and pain sensitivity of dairy calves following cautery dehorning with a local anesthetic. — J. Dairy Sci. 93: 2450-2457.
Hennessy, M.B., McCowan, B., Jiang, J. & Capitanio, J.P. (2014). Depressive-like behavioral response of adult male rhesus monkeys during routine animal husbandry procedure. — Front. Behav. Neurosci. 8: 1-8.
Hennessy, M.B., Chun, K. & Capitanio, J.P. (2017). Depressive-like behavior, its sensitization, social buffering, and altered cytokine responses in rhesus macaques moved from outdoor social groups to indoor housing. — Soc. Neurosci. 12: 65-75.
Henningsen, K., Andreasen, J.T., Bouzinova, E.V., Jayatissa, M.N., Jensen, M.S., Redrobe, J.P. & Wiborg, O. (2009). Cognitive deficits in the rat chronic mild stress model for depression: relation to anhedonic-like responses. — Behav. Brain Res. 198: 136-141.
Henry, S., Hemery, D., Richard, M.A. & Hausberger, M. (2005). Human-mare relationships and behaviour of foals toward humans. — Appl. Anim. Behav. Sci. 93: 341-362.
Henry, S., Richard-Yris, M.A. & Hausberger, M. (2007). Influence of various early human–foal interferences on subsequent human–foal relationship. — J. Int. Soc. Dev. Psychobiol. 48: 712-718.
Henry, S., Richard-Yris, M.A., Tordjman, S. & Hausberger, M. (2009). Neonatal handling affects durably bonding and social development. — PLoS ONE 4: e5216.
Hill, M.N., Hellemans, K.G.C., Verma, P., Gorzalka, B.B. & Weinberg, J. (2012). Neurobiology of chronic mild stress: parallels to major depression. — Neurosci. Biobehav. Rev. 36: 2085-2117.
Himmerich, H., Patsalos, O., Lichtblau, N., Ibrahim, M.A.A. & Dalton, B. (2019). Cytokine research in depression: principles, challenges, and open questions. — Front. Psychiatr. 10: 30.
Hinde, R.A. (1972). Mother-infant separation in rhesus monkeys. — J. Psychosom. Res. 16: 227-228.
Hinde, R.A. & Spencer-Booth, Y. (1971). Effects of brief separation from mother on rhesus monkeys. — Science 173: 111-118.
Hirschfeld, R.M.A. (2001). The comorbidity of major depression and anxiety disorders: recognition and management in primary care. — Prim. Care Companion J. Clin. Psychiatr. 3: 244-254.
Jayatissa, M.N., Bisgaard, C.F., West, M.J. & Wiborg, O. (2008). The number of granule cells in rat hippocampus is reduced after chronic mild stress and re-established after chronic escitalopram treatment. — Neuropharmacology 54: 530-541.
Jones, M.A., Mason, G.J. & Pillay, N. (2011). Correlates of birth origin effects on the development of stereotypic behaviour in striped mice, Rhabdomys. — Anim. Behav. 82: 149-159.
Jurgens, H.A. & Johnson, R.W. (2012). Environmental enrichment attenuates hippocampal neuroinflammation and improves cognitive function during influenza infection. — Brain. Behav. Immun. 26: 1006-1016.
Juruena, M.F., Bocharova, M., Agustini, B. & Young, A.H. (2018). Atypical depression and non-atypical depression: is HPA axis function a biomarker? A systematic review. — J. Affect. Disord. 233: 45-67.
Kalhagen, A. (2019). Signs that your bird is depressed. — Spruce Pets. https://www.thesprucepets.com/signs-that-your-bird-is-depressed-390423.
Kaufman, I.C. & Rosenblum, L.A. (1967). The reaction to separation in infant monkeys: anaclitic depression and conservation-withdrawal. — Psychosom. Med. 29: 648-756.
Kempermann, G., Kuhn, H.G. & Gage, F.H. (1997). More hippocampal neurons in adult mice living in an enriched environment. — Nature 386: 493-495.
Klein, A.B., Williamson, R., Santini, M.A., Clemmensen, C., Ettrup, A., Rios, M., Knudsen, G.M. & Aznar, S. (2011). Blood BDNF concentrations reflect brain-tissue BDNF levels across species. — Int. J. Neuropsychopharmacol. 14: 347-353.
Knorr, U., Vinberg, M., Kessing, L.V. & Wetterslev, J. (2010). Salivary cortisol in depressed patients versus control persons: a systematic review and meta-analysis. — Psychoneuroendocrinology 35: 1275-1286.
Kompagne, H., Bárdos, G., Szénási, G., Gacsályi, I., Hársing, L.G. & Lévay, G. (2008). Chronic mild stress generates clear depressive but ambiguous anxiety-like behaviour in rats. — Behav. Brain Res. 193: 311-314.
Kongara, K., Dukkipati, V.S.R., Tai, H.M., Heiser, A., Murray, A., Webster, J. & Johnson, C.B. (2020). Differential transcription of selected cytokine and neuroactive ligand-receptor genes in peripheral leukocytes from calves in response to cautery disbudding. — Animals 10: 1-14.
Konok, V., Kosztolányi, A., Rainer, W., Mutschler, B., Halsband, U. & Miklósi, Á. (2015). Influence of owners’ attachment style and personality on their dogs’ (Canis familiaris) separation-related disorder. — PLoS ONE 10: e0118375.
Korkmaz, M., Saritaş, Z.K., Bülbül, A. & Demirkan, İ. (2015). Effect of pre-emptive dexketoprofen trometamol on acute cortisol, inflammatory response and oxidative stress to hot-iron disbudding in calves. — Kafkas Univ. Vet. Fak. Derg. 21: 563-568.
Kornum, B.R. & Knudsen, G.M. (2011). Cognitive testing of pigs (Sus scrofa) in translational biobehavioral research. — Neurosci. Biobehav. Rev. 35: 437-451.
Lagisz, M., Zidar, J., Nakagawa, S., Neville, V., Sorato, E., Paul, E.S., Bateson, M., Mendl, M. & Løvlie, H. (2020). Optimism, pessimism and judgement bias in animals: a systematic review and meta-analysis. — Neurosci. Biobehav. Rev. 118: 3-17.
Laudenslager, M.L., Held, P.E., Boccia, M.L., Reite, M.L. & Cohen, J.J. (1990). Behavioral and immunological consequences of brief mother-infant separation: a species comparison. — Dev. Psychobiol. 23: 247-264.
Laudenslager, M.L., Boccia, M.L., Berger, C.L., Gennaro-Ruggles, M.M., McFerran, B. & Reite, M.L. (1995). Total cortisol, free cortisol, and growth hormone associated with brief social separation experiences in young macaques. — Dev. Psychobiol. 28: 199-211.
Lecorps, B., Nogues, E., von Keyserlingk, M.A.G. & Weary, D.M. (2020). Pessimistic dairy calves are more vulnerable to pain-induced anhedonia. — PLoS ONE 15: e0242100.
Lesimple, C., Fureix, C., Menguy, H. & Hausberger, M. (2010). Human direct actions may alter animal welfare, a study on horses (Equus caballus). — PLoS ONE 5: e10257.
Lessard, D. (2017). How to know if your dog is depressed... and what to do about it. — Available online at https://www.homeoanimal.com/blogs/blog-pet-health/how-to-know-if-your-dog-is-depressed-and-what-to-do-about-it.
Li, X., Xu, F., Xie, L., Ji, Y., Cheng, K., Zhou, Q., Wang, T., Shively, C., Wu, Q., Gong, W., Fang, L., Zhan, Q., Melgiri, N.D. & Xie, P. (2013). Depression-like behavioral phenotypes by social and social plus visual isolation in the adult female Macaca fascicularis. — PLoS ONE 8: e73293.
Liu, D., Xie, K., Yang, X., Gu, J., Ge, L., Wang, X. & Wang, Z. (2014). Resveratrol reverses the effects of chronic unpredictable mild stress on behavior, serum corticosterone levels and BDNF expression in rats. — Behav. Brain Res. 264: 9-16.
Lu, Y., Ho, C.S., Liu, X., Chua, A.N., Wang, W., McIntyre, R.S. & Ho, R.C. (2017). Chronic administration of fluoxetine and pro-inflammatory cytokine change in a rat model of depression. — PLoS ONE 12: e0186700.
Luo, D.D., An, S.C. & Zhang, X. (2008). Involvement of hippocampal serotonin and neuropeptide Y in depression induced by chronic unpredicted mild stress. — Brain Res. Bull. 77: 8-12.
Luo, L., Reimert, I., Graat, E.A.M., Smeets, S., Kemp, B. & Bolhuis, J.E. (2020). Effects of early life and current housing on sensitivity to reward loss in a successive negative contrast test in pigs. — Anim. Cogn. 23: 121-130.
Luo, Y., Cao, Z., Wang, D., Wu, L., Li, Y., Sun, W. & Zhu, Y. (2014). Dynamic study of the hippocampal volume by structural MRI in a rat model of depression. — Neurol. Sci. 35: 1777-1783.
Luppino, F.S., de Wit, L.M., Bouvy, P.F., Stijnen, T., Cuijpers, P., Penninx, B.W.J.H. & Zitman, F.G. (2010). Overweight, obesity, and depression. — Arch. Gen. Psychiatr. 67: 220-229.
MacLellan, A. & Mason, G. (2021). Characteristics of waking inactivity in mice: what does it mean and how can it be objectively assessed? — Oral Presentation for ‘What do specific forms of inactivity tell us about non-human animal affective (welfare) states?’ Workshop, online.
Maes, M., Meltzer, H.Y., Scharpé, S., Cooreman, W., Uyttenbroeck, W., Suy, E., Vandervorst, C., Calabrese, J., Raus, J. & Cosyns, P. (1993). Psychomotor retardation, anorexia, weight loss, sleep disturbances, and loss of energy: psychopathological correlates of hyperhaptoglobinemia during major depression. — Psychiatr. Res. 47: 229-241.
Malkesman, O., Scattoni, M.L., Paredes, D., Tragon, T., Pearson, B., Shaltiel, G., Chen, G., Crawley, J.N. & Manji, H.K. (2010). The female urine sniffing test: a novel approach for assessing reward-seeking behavior in rodents. — Biol. Psychiatr. 67: 864-871.
Marashi, V., Barnekow, A., Ossendorf, E. & Sachser, N. (2003). Effects of different forms of environmental enrichment on behavioral, endocrinological, and immunological parameters in male mice. — Horm. Behav. 43: 281-292.
Marazziti, D., Consoli, G., Picchetti, M., Carlini, M. & Faravelli, L. (2010). Cognitive impairment in major depression. — Eur. J. Pharmacol. 626: 83-86.
Marchese, G., Scheggi, S., Secci, M.E., De Montis, M.G. & Gambarana, C. (2013). Anti-anhedonic activity of long-term lithium treatment in rats exposed to repeated unavoidable stress. — Int. J. Neuropsychopharmacol. 16: 1611-1621.
Marino, L. (2020). Mental health issues in captive cetaceans. — In: Mental health and well-being in animals, 2nd edn. (McMillan, F.D., ed.). CABI, Wallingford, p. 315-327.
Marino, L. & Colvin, C.M. (2015). Thinking pigs: A comparative review of cognition, emotion, and personality in Sus domesticus. — Int. J. Comp. Psychol. 28: 1-27.
Mason, G.J. (2010). Species differences in responses to captivity: stress, welfare and the comparative method. — Trends Ecol. Evol. 25: 713-721.
Mason, G.J. (2011). Invertebrate welfare: where is the real evidence for conscious affective states? — Trends Ecol. Evol. 26: 212-213.
Mathews, A. & MacLeod, C. (1994). Cognitive approaches to emotions. — Annu. Rev. Psychol. 45: 25-50.
McGlinchey, J.B., Zimmerman, M., Young, D. & Chelminski, I. (2006). Diagnosing major depressive disorder VIII: are some symptoms better than others? — J. Nerv. Ment. Dis. 194: 785-790.
McGreevy, P.D. & McLean, A. (2005). Behavioural problems with the ridden horse. — In: The domestic horse, the origins, development and management of its behaviour (Mills, D.S. & McDonnell, S.M., eds). Cambridge University Press, Cambridge, p. 196-211.
McGreevy, P.D., Cripps, P.J., French, N.P., Green, L.E. & Nicol, C.J. (1995). Management factors associated with stereotypic and redirected behaviour in the Thoroughbred horse. — Equine Vet. J. 27: 86-91.
McKinney, W.T. & Bunney, W.E. (1969). Animal model of depression. — Arch. Gen. Psychiatr. 21: 240-248.
McKinney, W.T., Suomie, S.J. & Harlow, J.F. (1972). Repetitive peer separations of juvenile-age rhesus monkeys. — Arch. Gen. Psychiatr. 27: 200-203.
McQuaid, R.J., Dunn, R., Jacobson-Pick, S., Anisman, H. & Audet, M.C. (2018). Post-weaning environmental enrichment in male CD-1 mice: impact on social behaviors, corticosterone levels and prefrontal cytokine expression in adulthood. — Front. Behav. Neurosci. 12: 1-11.
Meagher, R.K., Campbell, D.L.M., Dallaire, J.A., Díez-León, M., Palme, R. & Mason, G.J. (2013). Sleeping tight or hiding in fright? The welfare implications of different subtypes of inactivity in mink. — Appl. Anim. Behav. Sci. 144: 138-146.
Mendl, M., Burman, O.H.P., Parker, R.M.A. & Paul, E.S. (2009). Cognitive bias as an indicator of animal emotion and welfare: emerging evidence and underlying mechanisms. — Appl. Anim. Behav. Sci. 118: 161-181.
Menneson, S., Ménicot, S., Ferret-Bernard, S., Guérin, S., Romé, V., Le Normand, L., Randuineau, G., Gambarota, G., Noirot, V., Etienne, P., Coquery, N. & Val-Laillet, D. (2019). Validation of a psychosocial chronic stress model in the pig using a multidisciplinary approach at the gut-brain and behavior levels. — Front. Behav. Neurosci. 13: 161.
Mifflin, K. (2020). Do dogs get depression? How to help your sad dog. — https://www.thesprucepets.com/do-dogs-get-depression-1112512.
Mills, D.S., Eckley, S. & Cooper, J.J. (2000). Thoroughbred bedding preferences, associated behaviour differences and their implications for equine welfare. — Anim. Sci. 70: 95-106.
Mineka, S., Suomi, S.J. & DeLizio, R. (1981). Multiple separations in adolescent monkeys: an opponent-process interpretation. — J. Exp. Psychol. Gen. 110: 56-85.
Mintline, E.M., Stewart, M., Rogers, A.R., Cox, N.R., Verkerk, G.A., Stookey, J.M., Webster, J.R. & Tucker, C.B. (2013). Play behavior as an indicator of animal welfare: disbudding in dairy calves. — Appl. Anim. Behav. Sci. 144: 22-30.
Mirra, A., Spadavecchia, C., Bruckmaier, R., Gutzwiller, A. & Casoni, D. (2018). Acute pain and peripheral sensitization following cautery disbudding in 1- and 4-week-old calves. — Physiol. Behav. 184: 248-260.
Murison, R. & Hansen, A.L. (2001). Reliability of the chronic mild stress paradigm: implications for research and animal welfare. — Integr. Physiol. Behav. Sci. 36: 266-274.
My Animals (2018). Depression in parrots: causes, symptoms and treatments. — Available online at https://myanimals.com/health/depression-in-parrots-causes-symptoms-and-treatments/.
Nasr, M.A.F., Nicol, C.J. & Murrell, J.C. (2012). Do laying hens with keel bone fractures experience pain? — PLoS ONE 7: e42420.
Nasr, M.A.F., Browne, W.J., Caplen, G., Hothersall, B., Murrell, J.C. & Nicol, C.J. (2013a). Positive affective state induced by opioid analgesia in laying hens with bone fractures. — Appl. Anim. Behav. Sci. 147: 127-131.
Nasr, M.A.F., Murrell, J. & Nicol, C.J. (2013b). The effect of keel fractures on egg production, feed and water consumption in individual laying hens. — Br. Poult. Sci. 54: 165-170.
National Farm Animal Care Council (2014). Code of practice: for the care and handling of pigs. — National Farm Animal Care Council, Lacombe, AB.
Naureen, A., Khan, M.S., Khan, M.A., Maqbool, A., Khan, J.A. & Avais, M. (2017). Stress status (mild, moderate and severe) viz’-a-viz’ leading risk factors among client-owned domesticated cats (Felis silvestris catus) affected with the ‘Pandora’ syndrome: a retrospective study. — J. Anim. Plant Sci. 27: 1155-1160.
Neave, H.W., Daros, R.R., Costa, J.H.C., Von Keyserlingk, M.A.G. & Weary, D.M. (2013). Pain and pessimism: dairy calves exhibit negative judgement bias following hot-iron disbudding. — PLoS ONE 8: e80556.
Nestler, E.J. & Hyman, S.E. (2010). Animal models of neuropsychiatric disorders. — Nature Neurosci. 13: 1161-1169.
Nip, E., Adcock, A., Nazal, B., MacLellan, A., Niel, L., Choleris, E., Levison, L. & Mason, G. (2019). Why are enriched mice nice? Investigating how environmental enrichment reduces agonism in female C57BL/6, DBA/2, and BALB/c mice. — Appl. Anim. Behav. Sci. 217: 73-82.
Nowacka, M. & Obuchowicz, E. (2013). BDNF and VEGF in pathogenesis of stress-induced affective diseases: an insight from experimental studies. — Pharmacol. Rep. 65: 535-546.
Olsen, C.M. (2011). Natural rewards, neuroplasticity, and non-drug addictions. — Neuropharmacology 61: 1109-1122.
Olsson, I.A.S. & Dahlborn, K. (2002). Improving housing conditions for laboratory mice: a review of “environmental enrichment”. — Lab. Anim. 36: 243-270.
Otte, C., Gold, S.M., Penninx, B.W., Pariante, C.M., Etkin, A., Fava, M., Mohr, D.C. & Schatzberg, A.F. (2016). Major depressive disorder. — Nat. Rev. Dis. Prim. 2: 1-20.
Paul, E.S., Harding, E.J. & Mendl, M. (2005). Measuring emotional processes in animals: the utility of a cognitive approach. — Neurosci. Biobehav. Rev. 29: 469-491.
Paul, E.S., Sher, S., Tamietto, M., Winkielman, P. & Mendl, M.T. (2020). Towards a comparative science of emotion: affect and consciousness in humans and animals. — Neurosci. Biobehav. Rev. 108: 749-770.
Peña-Guzmán, D.M. (2017). Can nonhuman animals commit suicide? — Anim. Sentience 2: 1-25.
Penninx, B.W.J.H., Milaneschi, Y., Lamers, F. & Vogelzangs, N. (2013). Understanding the somatic consequences of depression: biological mechanisms and the role of depression symptom profile. — BMC Med. 11: 129.
Perera, T.D., Dwork, A.J., Keegan, K.A., Thirumangalakudi, L., Lipira, C.M., Joyce, N., Lange, C., Higley, J.D., Rosoklija, G., Hen, R., Sackeim, H.A. & Coplan, J.D. (2011). Necessity of hippocampal neurogenesis for the therapeutic action of antidepressants in adult nonhuman primates. — PLoS ONE 6: e17600.