The evidence is clear: Horses suffer if key needs are not met – review

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"When combinations of social contact, free movement and access to roughage were restricted, many of the horses had developed responses consistent with suffering."
“When combinations of social contact, free movement and access to roughage were restricted, many of the horses had developed responses consistent with suffering,” researchers found after reviewing 38 studies. Photo by Jan Paul Yap

Evidence is compelling that horses require social contact, free movement and access to roughage to meet their basic needs, according to the authors of a just-published review.

Every animal species has particular environmental requirements that are essential for its welfare, Konstanze Krueger and her fellow researchers wrote in the journal Animals.

When these so-called “basic needs” are not fulfilled, the animals suffer.

In horses, it is asserted that these needs include social contact, social companionship, free movement and access to roughage in the form of grass, hay and/or straw.

To validate this claim, the review team examined 38 studies that reported on horses’ responses when one or more of these factors were restricted.

The authors categorised each type of response investigated into one of the groups:

  • Stress (for example, increased stress hormones);
  • Active response (such as increased aggression);
  • Passive responses (for example, depressive-like behaviour); and
  • Abnormal behaviours (such as stereotypies).

They then analysed the frequencies with which the investigated responses were shown.

The limited number of studies available on single management restrictions did not allow conclusions to be drawn on the effect of each restriction separately, especially in the case of social companionship, they said. “However, when combinations of social contact, free movement and access to roughage were restricted, many of the horses had developed responses consistent with suffering.”

It was clear, they said, that the three are basic needs in horses that need to be taken into consideration to ensure their mental and physical welfare in management and training.

Discussing their findings, the authors said a combination of several physiological and behavioural stress parameters may provide the strongest evidence for stress in horses, as some studies found conflicting results when comparing a limited spectrum of physiological and behavioural data.

“However, the proportion of horses showing passive responses supports the claim that many horses suffer long-term stress under the investigated management restrictions.”

Passive responses, such as reductions in activity, feeding, behaviour displays, contact with people or other horses, and reactions to the environment, indicate that horses withdraw from external stimuli and may show a depressive-like state, they said. “These responses are maladaptive for animals such as horses, which are both flight animals that rely on fast responses to acute challenges, and social animals that rely on fast responses to social challenges.”

Interestingly, the analysis of active responses did not provide a clear conclusion.

“Some studies reported that horses showed active responses when the animals were faced with restricted basic needs and others did not. It may be difficult to clearly distinguish the level of activity that constitutes a stress response, as elevated aggression and movement may counteract mild stress.”

The review team said very few studies succeeded in isolating the effects of restrictions in just one of the four proposed basic needs of social contact, social companionship, free movement and access to roughage. A clear statement on whether animals can generally cope with the particular restrictions therefore remains elusive.

“However, there were sufficient studies on combined restrictions in social contact, free movement and access to roughage, and when the horses’ environments were restricted in these three conditions, they appeared to suffer,” they said. In such cases, abnormal behaviours and passive responses had clearly developed.

The review team concluded that the development of abnormal behaviours and passive coping strategies can be considered signs of suffering. These were displayed under separate restrictions in social contact, free movement and free access to roughage, as well as under combined restrictions of two or more of the proposed basic needs.

Krueger is a German zoologist and behaviour researcher who is professor of horse management at the Nürtingen-Geislingen University of Applied Science. The other members of the review team were Laureen Esch, Kate Farmer and Isabell Marr.

Krueger, K.; Esch, L.; Farmer, K.; Marr, I. Basic Needs in Horses?—A Literature Review. Animals 2021, 11, 1798. https://doi.org/10.3390/ani11061798

The review, published under a Creative Commons License, can be read here.

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