Most lameness problems involve the foot. When a horse's foot is sore, it may be obvious, but sometimes it takes careful evaluation of the gait and examination of the feet to figure out which foot is sore and where.
The walk may not reveal much unless the horse is quite sore, whereas the trot is an ideal gait for spotting lameness. The horse is traveling faster, putting more force on the foot or leg (making it more painful).
He also makes more obvious deviation as he seeks to compensate, since the trot is the most regular and symmetrical gait. Diagonal legs strike the ground together.
It's more difficult to detect a lame leg at a canter/gallop because it's easier for a horse to minimize lameness, especially if he uses the lead that reduces strain on the sore leg.
The horse compensates for pain by getting off that leg as quickly as possible, moving his other legs and his body to take more of the weight. It's these compensatory movements that signal lameness.
Head carriage is the most obvious clue, since he uses head and neck for balance, just as a person swings arms and legs while walking or running.
At the walk and canter, the horse's head bobs at each stride.
At a trot, however, his head remains steady since he always has a leg at each side and each end of his body coming to ground at the same time. He doesn't need his head for balance.
Front leg lameness
If there's head-bobbing at the trot, he's lame, trying to shift his weight off a sore foot or leg by making extra balancing movement with head and neck.
To check for lameness, have someone lead the horse at a trot, directly away from you, and back again - with enough slack in the lead rope so the horse's head is free and you can see any head-bobbing. Also watch from the side as the horse is led past at a trot.
The key point is to note the timing of an exaggerated head elevation at the trot. When the painful front leg hits the ground, the horse will elevate his head to lessen the impact on that leg. While not easy for beginners, watching the head movements and the foot fall is key to helping decide which limb is affected.
Use a straight background like a fence or shed roof to provide a level reference point. This can help you see a non-symmetrical head bob or a drop of the withers or hip when the horse lands on the good leg.
The horse can also be longed or led in a circle both directions. Some lameness show up when making a turn, putting more stress or pressure on the inside or outside of feet or legs.
A hard surface will accentuate some types of lameness, due to increased concussion. A soft surface, in which the foot sinks in and the sole bears weight, will increase lameness if the sole or tissues above it are involved.
Another clue is how the horse stands at rest - if he tries to take weight off a front foot by standing with it more forward, or rests a hind foot.
Back leg lameness
Compensation movements for a hind leg lameness are harder to detect than for a front leg. The horse may only bob his head for severe hind leg pain - and this may be misinterpreted as lameness in a front leg.
A more reliable way to pinpoint hind leg lameness is to stand behind him as he is led directly away from you, to compare the up-and-down movement of his hips.
If pain occurs early in the stride as the lame foot takes weight, the rest of the stride will be shortened; the hip will pop up as the horse gets off that leg quickly. Again, the rising movement of the hip associated with the foot fall of the painful leg is the diagnostic
To evaluate hip movement, imagine a big T on the back end of the horse while standing behind him, with the tail dividing the hind quarters in half and the top of the T connecting the points of the hips. As the horse moves, the rise and fall of the hips will be obvious as you envision this horizontal line.
It's also fairly easy to detect hind leg lameness while observing the horse as he is trotted past. He protects the lame leg by getting off it faster and putting increased force and downward movement on the good leg. He also takes a shorter stride on the lame leg. This is very obvious on a video if it's played in slow motion
Leg lameness dilemma - not always easy to tell
Even veterinarians have problems identifying the sore limb on occasions. Sometimes subtle rear lameness may cause a head bob indicative of a fore limb lameness. Sometimes, multiple limbs may be lame, or another condition may be causing lameness that presents in a different manner. Veterinarians are skilled at observing the whole horse, and taking in the clues required for a more definitive diagnosis and plan of treatment.
Pinpointing the area of soreness
Once you determine which leg is sore, the next step is to locate the problem. The first place to look, if a horse is reluctant to put full weight on a leg, is the foot. The problem may be as simple as a rock wedged in it.
Or there may be indication of trauma or infection, such as a puncture or an advanced case of thrush. If there is nothing obvious, you may need a hoof tester to see if there's a sore area which might indicate a bruise or abscess under the sole.
If the bottom of the foot seems fine, check for heat in the hoof wall. Compare warmth or coolness of the other feet. This is easiest in early morning when all hooves would be cool. On a hot afternoon they will all be warmer.
Check for pain around the coronary band by squeezing the coronet and heels with your hands, and compare digital pulses of both feet.
Also compare the joints for thickness and swelling, heat or sensitivity. Your hands can often give clues that are hard to see, and the horses reaction to touch or pressure tells you if an area is sore.
If you are still at a loss, check the leg from top to bottom for heat and swelling, and the opposite leg also, for comparison. This is where the skill, training and knowledge of a veterinarian is important. Especially in performance or show horses, only the veterinarian can determine the joint, ligament or tendon that may be damaged, and provide a treatment plan.
By checking horses' feet and legs daily - during grooming, before and after a ride, and the day after a hard workout - lameness will be apparent at an early stage.
Once you locate the area of soreness, the next step is to determine what caused it (whether injury or infection) and what to do about it.
Get help from your veterinarian for diagnosis, and almost always should consult him/her for advice on the most effective treatment, unless it's something simple like a rock caught in the shoe.