Hospitalized horses tend to “perk up” in the presence of people, according to researchers, which may have important implications in terms of assessing and managing their pain.
The study was carried out by Catherine Torcivia and Sue McDonnell at the University of Pennsylvania School of Veterinary Medicine.
The pair, writing in the open-access journal Animals, noted that horses have evolved to show little indication of discomfort or disability when in the presence of potential predators, including humans.
“It has been our clinical impression that, whenever a person is present, horses tend to ‘perk up’ and ongoing discomfort behavior more or less ceases,” they say.
“This natural characteristic complicates the recognition of pain in equine patients.”
The pair said that although this apparent tendency for interruption of observable discomfort behavior in the presence of people has been mentioned in previous studies, it does not appear to be widely appreciated in equine clinical practice.
The pair set out to evaluate and describe this effect.
The study involved 20 client-owned horses admitted to the large animal hospital at the University of Pennsylvania’s New Bolton Center. They comprised a mix of breeds and ages.
Each horse, housed in an individual stall, was kept under 24-hour video surveillance. Other horses occupied surrounding stalls.
Each horse received a caregiver visit, either to observe and examine the horse, or provide treatment.
The study was set up to ensure there were no other human visitors to the barn for one hour before the visit, and one hour after.
The visits ranged from about three-and-a-half minutes to nearly eight minutes.
The recorded footage of the visit, and the hour before and after, were then analysed by a veterinarian experienced in recognising 65 observable horse behaviors associated with discomfort.
These range from shifting weight, pawing and difficulty in getting up through to head tossing, tail swishing, weaving and pinned ears.
For each horse, the number of specific discomfort behaviors per minute were calculated for each phase — the hour before and after the visit, as well as the visit itself.
A total of 33 distinct behavioral indicators of discomfort were seen.
Across all the horses, the number of discomfort behaviors before the visits averaged 1.60 per minute. After the visit, they averaged 1.49 per minute, which the researchers said was not a significant difference. In contrast, the average number of discomfort behaviors per minute during the visit was just 0.40.
This represents a reduction of 77.4%. For six of the horses, observed discomfort behaviors ceased altogether during the visit.
Torcivia and McDonnell said the results clearly confirm their clinical impression that ongoing discomfort behavior in hospitalized horses is conspicuously interrupted when people approach or interact.
“This sample involved only orthopedic surgery patients. Our experience has been that similar disruption of ongoing discomfort behavior occurs with discomfort resulting from sources other than musculoskeletal.
“While especially of welfare concern with hospitalized patients, this tendency to show little indication of discomfort or disability in the presence of potential predators likely similarly delays recognition of injury or disease in horses in general.”
They said they were concerned that this significant reduction in observable discomfort behavior in the presence of a person is not widely appreciated in equine practice.
“We suggest that equine pain evaluations be conducted remotely via video monitoring, when the hospital environment is otherwise quiet and the horse is undisturbed.
“An ideal method would be to obtain a video sample, longer than one might observe in-person, that can be immediately viewed in fast forward to better appreciate frequency and repetitiveness of discomfort behaviors.
“Video viewing technicians typically learn very quickly how to recognize discomfort behavior when viewing in fast forward. In our lab, new technicians typically achieve acceptable levels of inter-observer reliabilities within a few hours of training.”
A one-hour video sample can be scanned at 10 to 20 times real time within a few minutes.
“The time commitment would be similar to that of a typical stall visit, yet provide greater information.”
Torcivia, C.; McDonnell, S. In-Person Caretaker Visits Disrupt Ongoing Discomfort Behavior in Hospitalized Equine Orthopedic Surgical Patients. Animals 2020, 10, 210.