New scoring system assesses chronic pain in horses

Chronic pain, especially when evolving gradually, can be difficult to assess in horses, yet it may greatly affect welfare.
Chronic pain, especially when evolving gradually, can be difficult to assess in horses, yet it may greatly affect welfare. Photo by BLMIdaho

A structured scale to measure chronic pain in horses has been developed by researchers in Europe.

Johannes van Loon and Lucia Macri, reporting in the journal Animals, said objective assessment of chronic pain is crucial for improving welfare and quality of life in horses.

Acute pain in horses can be objectively assessed using different types of pain scales. Chronic pain, especially when gradually evolved, can be difficult to assess, yet it may greatly influence equine welfare, they said.

To date, no studies have been conducted to develop a structured pain-measuring tool for the assessment of ongoing pain in horses seen with the likes of osteoarthritis or persistent laminitis.

In donkeys, a pain scale incorporating behavioural and facial expression-based parameters has been shown to help in assessing chronic pain.

Van Loon, with the Department of Equine Sciences at Utrecht University in The Netherlands, and Macri, with the Equine Department at the University of Zürich in Switzerland, used the same concept to develop a pain scale to measure chronic pain in horses.

The scale, dubbed the Horse Chronic Pain Scale, HCPS, is based on behavioural parameters and facial expressions.

The scale was tested in 26 horses with different types of chronic pain — osteoarthritis, chronic laminitis, chronic back and neck problems, and chronic dental disorders — and 27 healthy control animals. All were older animals located at a retirement home for elderly horses in The Netherlands. These conditions were considered mild by the attending veterinarian and did not require pain-relieving treatment.

The animals were assessed once daily for three consecutive days by van Loon and Macri, who were blinded to the condition of the animals and unaware of any pain-relieving treatment regimens.

The HCPS consists of two parts, the Horse Chronic Pain Composite Pain Scale (HCP CPS, with behavioural parameters) and the EQUUS-FAP (Equine Utrecht University Scale for Facial Assessment of Pain).

The HCP CPS was developed from the composite pain scale for the assessment of chronic pain in donkeys and was tested in a pilot study with 10 healthy horses not included in the current study.

The combination of these two scales — HCP CPS and  EQUUS-FAP (the scores from both scales were added)  — resulted in the Horse Chronic Pain Scale (HCPS).

The HCP CPS takes into account the likes of general appearance, body posture, head carriage, weight-shifting, eating performance, musculature, body condition score, the horse’s reactions, movement, and response to flexion tests. The EQUUS-FAP explores factors including head movement and the appearance of the eyelids, nostrils, lips and ears.

Van Loon and Macri found the HCPS to be a reproducible pain scale and useful to assess chronic pain in horses.

“Further studies are needed to confirm these findings in other horses and to validate its use in subsets of horses with specific chronic pain states,” they said.

The authors said the most obvious differences between horses with and without chronically painful conditions were found in the composite pain scale parameters. Facial expressions proved less sensitive for chronic pain.

In follow-up studies, newly enrolled horses with or without chronic pain will need to be evaluated, to further refine and validate the current pain scale and to investigate its usefulness.

In these follow-up studies, non-geriatric horses that are used for ridden work could also be included to assess whether the scale could be used for the valid assessment of chronic pain in these horses.

van Loon, J.P.A.M.; Macri, L. Objective Assessment of Chronic Pain in Horses Using the Horse Chronic Pain Scale (HCPS): A Scale-Construction Study. Animals 2021, 11, 1826.

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

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