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Review
. 2023 Apr 28;13(9):1507.
doi: 10.3390/ani13091507.

Mental Experiences in Wild Animals: Scientifically Validating Measurable Welfare Indicators in Free-Roaming Horses

Andrea M Harvey  1 , Ngaio J Beausoleil  2 , Daniel Ramp  1 , David J Mellor  2
Affiliations
Review

Mental Experiences in Wild Animals: Scientifically Validating Measurable Welfare Indicators in Free-Roaming Horses

Andrea M Harvey et al. Animals (Basel). .

Abstract

The mental experiences of animals are what characterises their welfare status. The Five Domains Model for assessing welfare aligns with the understanding that physical and mental states are linked. Following measurement of indicators within each of the four physical/functional Domains (1. Nutrition; 2. Physical environment; 3. Health; and 4. Behavioural interactions), the anticipated negative or positive affective consequences (mental experiences) are cautiously inferred and assigned to Domain 5. Those inferences derive credibility from validated knowledge of the underlying systems of physiology, neurophysiology, neuroethology and affective neuroscience. Any indicators used for assessing welfare need to be scientifically validated. This requires, firstly, evidence of the links between a measurable/observable indicator and the physical/functional impact (in Domains 1 to 4), and secondly, a demonstrable relationship between the physical/functional impact and the mental experience it is inferred the indicators reflect (in Domain five). This review refers to indicators of physical/functional states in Domains 1 to 4, which have been shown to be measurable in free-roaming wild horses, and then evaluates the scientific evidence linking them to inferred mental experiences in Domain 5. This is the first time that the scientific evidence validating a comprehensive range of welfare indicators has been synthesised in this way. Inserting these indicators into the Five Domains Model enables transparently justifiable assessment and grading of welfare status in free-roaming horses.

Keywords: Five Domains Model; affective state; free-roaming horse; horse; mental experience; scientific support; validation; welfare assessment; welfare indicators; wild animal; wild horse; wildlife.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
An abbreviated schema of the Five Domains Model (adapted from Harvey et al., 2020 [2]), showing negative and positive physical/functional states or situations (Domains 1 to 4) and examples of their associated negative and positive mental experiences or affects (Domain 5), relevant to free-roaming wild horses. Taken together, these mental experiences represent the overall welfare state of the animal.
Figure 2
Figure 2
A low BCS is a scientifically validated indicator of hunger. Image: A.M. Harvey.
Figure 3
Figure 3
Horses exhibiting cooling behaviour by immersing themselves in cool water to mitigate heat discomfort. Image: A.M. Harvey.
Figure 4
Figure 4
A cutaneous wound on the hindlimb of a horse. In this location, additional impacts on the underlying extensor tendon or tarsal joint may be present. The extent of such additional impacts will determine the severity of pain associated with the wound. Image: A.M. Harvey.
Figure 5
Figure 5
Red arrow illustrates left-sided food pouching in a captured wild young stallion. Image: A.M. Harvey.
Figure 6
Figure 6
A corneal ulcer (red arrow) that was associated with corneal oedema (blue arrow) and blepharospasm, suggestive of the mental experience of acute ocular pain. Image: A.M. Harvey.
Figure 7
Figure 7
Severe injury of the lower left limb in a wild horse causing lameness, indicating presence of severe lower limb pain. Image: A.M. Harvey.
Figure 8
Figure 8
Camera trap image demonstrating head lower than withers posture in a thin wild horse, suggestive of mental experiences of chronic pain/malaise/fatigue/exhaustion. Image: A.M. Harvey.
Figure 9
Figure 9
A camera trap image of a wild horse demonstrating some features of the facial grimace, suggestive of the mental experiences of pain, malaise, or exhaustion. Image: A.M. Harvey.
Figure 10
Figure 10
An emaciated wild horse that was observed to have both reduced activity and vigilance, suggestive of mental experiences of malaise, fatigue, and exhaustion. Image: A.M. Harvey.
Figure 11
Figure 11
Wild horses fleeing from human disturbance, suggestive of the mental experiences of anxiety/fear/panic. Image: A.M. Harvey.
Figure 12
Figure 12
Standing resting after a period of grazing, indicative of post-prandial satiety. Image: A.M. Harvey.
Figure 13
Figure 13
A bachelor stallion that has galloped over to investigate the photographer. The curiosity, locomotion, good health, and physical fitness may indicate vitality of fitness. Image: A.M. Harvey.
Figure 14
Figure 14
A band of wild horses demonstrating a range of rewarding behaviours, including exercise of agency, engaged foraging, standing resting, lying resting, affiliative social interactions and maternal nurturing, indicative of a range of associated positive mental experiences. Image: A.M. Harvey.
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References

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Grants and funding

This research received no external funding. A.M.H. was supported by an Australian Government Research Training Program scholarship and University of Technology Sydney Chancellor’s Research scholarship during this work and is currently funded by a University of Technology Sydney Chancellor’s Post-Doctoral Fellowship.

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