A horse walks into a bar and the barman says, “Hey buddy, why the long face?”
It may be the oldest horse joke in the book, but researchers are making serious progress in deciphering the facial expressions of horses.
Experts have developed a new standardized scale of facial expressions to help horse managers discern pain.
Through the results of a recent study, researchers from Italy, Germany and Britain have developed what they are describing as the standardized Horse Grimace Scale (HGS) to assist in pain detection in horses.
Dr Michela Minero, who presented the research group’s findings at the recent 2013 annual conference of the International Society for Equitation Science in the United States, said the scale could assist the welfare of horses who have undergone routine surgical procedures such as castration.
“The standardized HGS is easily trainable to laypersons and may be beneficial to those in the position of managing horses that have undergone painful procedures,” Minero said.
Only a minority of horses undergoing routine castration in Europe receive postoperative pain control, even though the procedure is known to be painful.
“Annually, it is estimated that 240,000 horses are castrated in Europe, and castration has been shown to be associated with a certain degree of pain,” Minero says.
“However, only about 36.9 percent of horses receive analgesics for post-operative pain. One of the possible explanations for this is that the assessment of pain in horses undergoing castration is still sub-optimal.”
Forty-six stallions of varying breeds, ranging in age from 1-5 years, were used in the study.
The horses were divided into one of two treatment groups and a control group. Treated horses underwent routine surgical castration using the closed technique.
Group A, comprising 19 horses, received one injection of Flunixin-Meglumine, commonly known as Banamine immediately prior to anaesthesia, while group B, made up of 21 horses, received the same drug both prior to anaesthesia and six hours post-operatively.
A control group of six horses requiring non-invasive diagnostic procedures under general anaesthesia were also used in the study.
All of the horses studied were hospitalized for five days. As a baseline, high definition videos of the horses were taken both for 30 minutes on the day prior to surgery, and eight hours post-operatively. Video recording continued over the five-day period, from which high quality images of the horses’ faces were extracted.
These images were then scored by five treatment-blind observers.
Subtle changes in facial expressions/changes indicative of communicating pain have been identified in other species, and the researchers hoped to be able to standardize such expressions in horses.
One complicating factor affecting assessment could be how and when the horse chooses to express pain.
Minero continues: “Because there is no verbal means of communication between animals and humans … this could be further compounded by the horse’s suppression in the expression of obvious signs of pain when in the presence of humans.”
The facial actions chosen to identify pain included: stiffly backward ears, orbital tightening, tension above the eye, strained chewing muscles, mouth strained and pronounced chin, strained nostrils, and flattening of the profile.
A treatment-blind observer, experienced in facial expression assessment in other species, reviewed the images to identify facial expression changes in the horses.
Pain-related behaviours occurred predominantly eight hours after the operation, suggesting this was a critical time for pain evaluation.
The results of the study showed both a high degree of accuracy (73.3 percent) in pain assessment, and a high level of inter-observer reliability.
The findings suggest that such a scale could indeed benefit those in the position of managing horses that have undergone painful procedures.
The researchers noted that darker coloured horses were harder to score than lighter ones.