Usually, a broken bone can be managed.
If your cat or dog breaks a leg, bandaging and a cast may be enough to make a full recovery. Even a bird that relies on two legs to support its weight can become temporarily 1-legged while the other leg heals in a bandage.
But, what happens when an animal can’t compensate for an injured limb?
In these situations, the prognosis is not very good, and often, such an animal doesn’t survive. Unfortunately, this is often the case with horses suffering significant fractures to one of their legs — but there may be hope!
In this article, I’m going to talk about some exciting research looking at how exercise intervention from an early age can help prevent injury in horses once they’ve reached adulthood.
Why are fractures so bad in horses?
When we are dealing with a fractured limb in a horse, there are a few factors that make successful treatment particularly difficult:
- Size – You can’t deny that horses are big animals. The average adult horse weighs between 900 – 2000 lbs depending on the breed! So, if we are trying to fix a fractured leg by using screws and plates, we have to hope these implants stay solid and resilient. This massive weight puts a lot of stress on implants!
- Standing posture – Horses need to stand and can’t be recumbent for extended periods. If your dog breaks a leg, then it can rest and lay down. Horses can’t do this. Because of their physiology, laying down for too long can lead to issues with their digestive system – leading to abdominal pain and colic. On top of that, the sheer weight of the horse can cause blood loss and nerve damage to the tissue receiving the pressure of the weight. Horses are healthiest when standing.
- Some fractures are irreparable – If the fracture occurs in the lower (distal) limb, there is plenty we can do to fix it. However, damage to significant bones like the femur or scapula is impossible to fix. In small animals, repairing these bones is challenging enough. Since horses are so large and can’t compensate with their other three legs, significant fractures in the proximal limb are often life-threatening. It just comes down to biomechanics.
Fractures in Racehorses
While any horse can develop a fracture from stepping in a hole or getting kicked by another horse, racehorses have an exceptionally high incidence of fractures in their distal limbs. This is because a racehorses’ exercise causes chronic stress and repetitive trauma, making these horses particularly susceptible to distal limb fractures.
This problem has made veterinarians and researchers wonder how we can improve the strength of these crucial bones from an early age to benefit the adult horse and prevent injury. With most lower limb fractures occurring between 2-10 years of age, we want to target the window before the skeleton reaches maturity (approximately four years of age).
Why do horses have weak bones in their distal limbs?
Bone develops in a “use it or lose it” kind of way. The more pressure and strain we apply to young bones, the more the bone will strengthen and adapt – this is called Wolff’s Law. So new bone is created preferentially in areas that experience mechanical stress and strain.
Let us look at the behaviour of puppies. They’ll have bursts of energy that allow the puppy to apply pressure to their developing bones naturally, and then they’ll have a resting period.
BUT when we look at young foals, we see them spending 85% of their time doing nothing. They sleep. They stand. They eat. This makes them naturally inactive at an early age and is likely to affect the development of sturdy bones once foals mature and are suddenly required to follow exercise routines.
From a practical point of view, it makes sense that we see a high incidence of lower limb fractures in adult horses since the foals were not regularly exerting stress and strain on these bones during development. Therefore, the sudden strain once the horse begins training comes as a bit of a shock to these ill-prepared bones.
The Exercise Intervention Study aims to prevent injury in horses
There is plenty of evidence that has shown that exercise improves bone strength and bone density. So inherently, researchers at the University of Illinois at Urbana-Champaign wanted to try and capitalize on Wolff’s Law to stimulate bone development at an earlier age in foals.
First, the researchers had to figure out what NORMAL foal development is. So they observed a group of foals on pasture and monitored their bone development and gait. Over one year, they noticed that as the foals would gain weight, the distal limb bones were disproportionately weaker than the other bones of the leg.
Next, they followed a cohort of 12 Standardbred foals at 8-weeks of age from a farm in Illinois, USA and split them into Control (6) and Experimental (6) groups.
- The Control Group would be let out on pasture to do what normal young horses do – roam and graze.
- The Experimental Group would be exposed to short periods of exercise, which consisted of 1,500 yards of fast trotting, five times a week for eight weeks.
To determine whether or not the exercise was helping improve bone development, they followed both the Control and Exercise groups closely. They performed analysis by CT imaging before (8 weeks old), during (16 weeks old), and after (1 year old). This allowed them to look slice-by-slice at HOW and WHERE the new bone was developing.
Ideally, they wanted to see that new bone was being developed in the areas prone to fracture once the foals reach maturity and begin training.
Although they are still validating their findings, preliminary data suggest that exposure to low-strain exercise between 8-16 weeks of age INCREASES bone development, compared to the control group.
Conclusion: How to Prevent Injury in Horses
So far, they have completed the analysis on one foal from each treatment group and have noticed a difference in the location of new bone development.
Non-Exercise Group (control) – Bone appeared to preferentially develop along the inside of the bone because the forces applied from standing will target the center of the bone the most – the medulla.
Exercise Group – Foals that DID exercise showed a different pattern of bone development that was more evenly distributed along the outside of the bone.
As the horses mature, the researchers plan to continue following these horses to assess the incidence of fractures. This will confirm whether exercise truly has a role in building stronger bones that prevent distal limb fractures in adult horses.
You can learn more about this study here.