There are lateral gaits and/or diagonal gaits that are required performance of the horses we shoe or trim. Some are natural lateral gaits, like Icelandic and Paso Fino horses, and some are learned, like five-gaited Saddlebred horses. This brief treatise will be on the diagonal gait of trot.

A diagonal gait, that when defined, should be symmetrical in sight and sound as we watch the horse perform it (provided the horse is not lame). Discrepancies of this gait can be different weight-bearing times, impact differences on the diagonal pairs and swing phase timing differences (where the horse must hold a leg in the air shortly to time the paired diagonal legs’ impact).

Some locomotion parameters define what is a correct trot gait and what is not. The defined trot gait in a free-moving sound horse is symmetrical in weight-bearing time, impact/departure timing (that is both diagonal feet impact and depart the ground at the same time) and swing phase, which also includes the suspension phase.

These symmetrical observations would be truer and easier to hear and see without a rider and on the line in a straight line (Figure 1). Riding or hooking to a buggy certainly changes the mechanics of the body and requires the horse to adjust those symmetrical temporal parameters. Normal adjustment by the horse is to shorten the weight-bearing phase in front to assist vertical lift and extend the weight-bearing phase in the rear to accommodate the increased horizontal load.

Oftentimes, riding or driving a horse (Figures 2a & 2b) helps farriers observe these compensated changes in temporal parameters. These compensations are predictable, and each horse will do so differently, dependent on multiple factors including the difficulty of the work (including substrate), body condition, soundness and conformation.

A normal adjustment by the horse is to shorten the weight-bearing phase in front to assist vertical lift and extend the weight-bearing phase in the rear to accommodate the increased horizontal load. Randy Luikart

Rider Weight

To understand the horse’s compensated adjustment, let’s look at the rider’s weight influence (ignore the rider’s horsemanship influence) on the horse. First, assuming you have a 1,000-pound horse and a 150-pound rider, the additional weight increases the horse’s propulsive requirement by at least 15%.

In his research on weight bearing and stride parameters, the late Dr. Steve Wickler of the University of Cal Poly Pomona found that 50 pounds (5% of a 1,000-pound horse) was enough weight to change those temporal parameters of the preferred gait stride and frequency (increase in frequency and shorter step distance). So, that 15% will influence how the horse must accommodate that extra weight.

Weight differences may not be linear from 5-15%. If you continue to increase the weight, it becomes more difficult for the horse to accommodate the weight. The horse would be unable to compensate for increased weight on its back with the magnitude of its own weight. More importantly, that additional 15% mass position in relation to the center of mass (i.e. in front of the CM, directly above the CM or behind the CM) would influence the distribution of that weight combined with the CM to heavy cranially, vertical effect, or heavy caudally, respectively.

The horse must compensate for these mechanical variables with subtle mechanical conformation alterations in its legs, accommodated by muscle firing. Oftentimes, postural changes are exhibited statically in addition to the dynamic changes the horse makes to maintain stability during movement.

Each horse has a symmetrical preferred gait stride length and frequency based on that horse’s body mass and conformation. Much like you have when you run, the stride length and frequency that you or the horse can run or trot the longest in time at the least amount of energy consumption is also the preferred gait stride and frequency of humans. Additionally, since the complete stride contains the weight-bearing phase, swing phase and suspension phase, the horse can adjust (with muscle control) the weight-bearing phase and/or swing phase with each leg being independently controlled.

In daily practice, alterations of these temporal parameters for a compensated load (or pain) is used by the industry to define lameness at best and gait asymmetry at the least. Some machines that measure these parameter differences are being used by veterinarians in diagnosing lameness daily. Utilization by practitioners and researchers to evaluate compensated changes in gait and differences in these temporal parameters can provide farriers an enlightened and quantitative perspective on how farrier techniques can also alter those temporal parameters.

Dr. Molly Nicodemus of Mississippi State has shown in her research that advance lift-off and advance placement timing defines the different breeds of gaited horses’ stride parameters.

If you believe that is overthinking the situation, put a 22½ pound sack (15% of your 150-pound body) and hang that sack over your chest, on top of your head, or behind your back and see how you modify your postural conformation to maintain stability.

Dr. Hilary Clayton states in her book Equine Locomotion that the horse must have stability before it has proper maneuverability. The stability comes from adequate support for loading and application. Stability also must be provided for those variable application requirements in reference to surface area or traction for the compensated forces involved in the movement of the horse and rider.

In real-world analogies, think about how effective it is to stand on your bike pedal while pedaling up a hill instead of sitting in the seat. Repositioning the CM over your leg and foot assists in utilizing your body mass to provide a more efficient vertical force function. The CM’s position and influence on the vertical and horizontal forces over weight-bearing structures should not be overlooked. The horse does all this automatically, just as we do. Unfortunately, the horse cannot change the rider’s position.

One of those defining features of temporal parameter timing change from a rider’s influence is that the front leg should have advanced lift-off (shorter weight-bearing step = more efficient position to lift) from the diagonal hind (Figures 3a & 3b).

One of those defining features of temporal parameter timing change from a rider’s influence is that the front leg should have advanced lift-off from the diagonal hind. Randy Luikart

The horse (just as you) takes a shorter step as increases in weight (and/or vertical influence) occur. The farther the rider sits behind the CM, the more influence the rider has on the front leg weight-bearing timing becoming shorter. Remember that the hind legs have less weight down them than the front, and if that diagonal was timed on a line, an increase in the horse’s gross weight means the horse must propel more weight horizontally (push) from the rear and vertically (increase in lift) in the front.

Compensation

Sound horses will accommodate this requirement by elongating the hind (increase in push) weight-bearing phase in time so that the hind leg muscles must work longer and slower to facilitate the change. That ensures the advanced lift-off in front timing. Muscle physiology people always claim it’s easier and more efficient for muscles to work longer and slower rather than harder and faster. Additionally, having the front legs free (airborne) of the ground allows the hind end to push the horse’s CM with little resistance.

In the front, the horse must lift more, and the time on the ground will be shorter with additional weight being added to its conformation. If the rider is sitting in front of the CM, that position has more of an influence vertically on the front legs than when sitting behind the CM, which has more influence on the hind legs. Essentially, adding a rider, pulling a buggy or anything that requires the horse to provide more push from the hind legs, enhances the advance lift off of the front legs. Look again at Figures 3a & 3b.

The hind leg staying on the ground longer than the front (or the front leg leaving the ground early) is how the horse will accommodate that mechanical change in force amplitude and position of the CM (or center of gravity with the rider) and biomechanically is called “advanced lift-off” of the front.

The gait has become a spinal reflex activity after about 3 years of age. The horse must use muscle control (and brain for that matter), physically overriding that spinal control, to change that parameter. That muscle override comes at a cost of energy efficiency.

You also can consciously change your weight-bearing phase to longer or shorter when ambulating, if you so desire, by muscle control. However, if we allow our brain to run our body, we instantly jump to our preferred weight-bearing and frequency, just as the horse does. The horse accommodates those mechanical conformational changes by muscle control actively expending energy to alter the timing.

Mechanical Augmentation

Mechanical changes employed in farrier techniques that do not complement the preferred or compensated gait parameters come at a higher cost of energy for the horse. In these pages, I wrote about timing of the front and back some time ago.

A farrier’s job is to provide mechanical augmentation of the physical requirements the horse has in the performance it’s being asked to do. In our example, it is just carrying a rider or pulling a buggy. If the horse is consciously lengthening its hind leg weight-bearing phase, how would we shoe it to accommodate that change so it becomes easier to make that adjustment by muscle firing?

Some of the examples to accomplish this that quickly come to mind include lengthening the hoof and lowering the angle or toe traction. Currently, in our profession, we obsessively and incorrectly are trained or advised to shorten the toe in the hind, back the shoe up and raise the angle of the hoof. 

That flies in the face of what the horse needs, especially since most of the horses of today are ridden. In the defined horse, the front and back hooves would be the same length and close to the same angle. Functionally, you could raise the angle a couple of degrees in the front, lower the angle in the back the same and allow the hind toe length to be a little longer. Not 1 inch, but enough to accommodate the 15% change in body weight from a rider. That would equate to a change of 7% in the front (shorter and faster step) and 7% in the rear (longer weight bearing and time) to be more precise.

These mechanical farrier changes are instantaneous. If you don’t think so, and the horse in front of you has been having an interference problem, you may need something to try. Take that hind bull nose or very short foot and place a wide-web shoe inner web barely on the foot base at the toe and allow the rest to stick in front of the toe. Fit the shoe in the quarters, punch nail holes where you might need them, nail it on and take the horse out and work it.

Instantly, (the rule of thumb is three steps) the gait will be altered. The rider will comment that the post in the saddle is more solid, canter leads will be easier from a slower speed, less interference front to back, and if you have a video camera handy, you will see a later departure of the hind foot from the paired diagonal. The separation in time and distance between the hind and front hoof will be greater. Compare what you had before (you must have recorded video before the change) with what you have now. It is obvious that you now have something to show the rider that what you did was effective. The horse does not have to “adjust” to those changes; it will be a positive alteration immediately.

One goal of shoeing performance horses is to augment positive mechanical changes in farrier techniques that en­hance the performance requirement. It’s quite possible to shoe a horse so advanced lift-off in the front will not occur. Instead, it occurs in the rear. That makes the hind leg early to the place where the front foot is, and you have interference, shoe pulling and possible lameness issues (Figures 4a-4c).

It’s possible to shoe a horse so advanced lift-off in the front will not occur. Rather, it will occur in the rear. It causes the hind leg to be early to the place where the front foot is. It results in interference, shoe pulling and possible lameness. Randy Luikart

Making it easier to break over is not the same as more efficient performance. Over-emphasizing the last few milliseconds of weight bearing in the hopes that modification will cover and protect all the mechanical discrepancies during the weight-bearing phase is foolish, to say the least.

There is a lot of misinformation out there (internet included). Occasionally, a farrier writes a thread describing taking over an account and shoeing the horses more “correctly” by backing up the shoes, raising the angle on the back feet and having the hind feet shorter than the fronts. Over time, the horse starts to remove its front shoes. It’s a common problem.

Often, other farriers will respond with, “You’re doing it right, just be more aggressive with backing the hind toes up.” Doing more of the same technique that isn’t working doesn’t make sense to me. Einstein called that insanity. Perhaps we might want to reconsider our standard accepted practices in managing timing discrepancies.