A new study underscores the importance of longeing a horse during a lameness exam, finding that it can reveal asymmetries so subtle that the horse appears sound.
Researchers at The Royal Veterinary College in England and Uppsala University in Sweden performed high-tech gait analysis on 23 horses considered sound by their owners. The horses were trotted both in-hand and on a longeline in both directions over a soft, sandy surface and hard asphalt. During the sessions, inertial sensors attached at various locations on each horse’s body measured his movement and collected data to quantify any asymmetry between pairs of limbs.
Using the inertial sensors allowed the detection of even the slightest asymmetry of movement, says Thilo Pfau, PhD.
“We were interested to see whether horses that are a little bit asymmetrical (i.e., mildly lame) on the straight will behave differently on the longe than horses that are ‘within normal limits’ [according to the data collected by the inertial sensors] when assessed on the straight,” says Pfau. “The important thing to remember is all these horses were considered sound by their owners, and the level of asymmetry that we can measure [with sensors] is very low, often below the 25 percent asymmetry that the human eye/brain needs to reliably detect movement asymmetry.”
With the sensors, even extremely mild asymmetries were evident on the longe line. “The horses within normal limits move very similarly for all four surface and rein combinations,” says Pfau. “The ones that are already slightly asymmetrical on the straight often show differences between surface and rein combinations.”
The difference was most obvious in cases of forelimb lameness when the lame leg was on the inside of a longeing circle. “We know there is a mechanical link between the head nod seen in lameness and force,” says Pfau. “There is more force acting on the limb when the head nods down. So if we make use of this mechanical link, then what we see here is that the horses take even more weight off the lame limb when this is on the inside of the circle.”
Pfau says that this study reinforces the importance of working a horse on a longe line not only during a clinical lameness exam, but also during assessments made with high-tech biomechanical measurement systems: “The human brain is a powerful tool and will take into account that the horse is longed. When we start measuring things we need to develop ‘compensation’ methods to deal with this ... this is why this work is important for anybody using a gait analysis system during lameness workups.”
Reference: “Longeing on hard and soft surfaces: Movement symmetry of trotting horses considered sound by their owners,” Equine Veterinary Journal, October 2014
This article first appeared in EQUUS issue #448, January 2015.