Stabling and ‘Slow Work’ Increases the Risk of Bone Injury in Racehorses

Long periods of slow work for racehorses has long been thought of as the best way to ‘leg up’ young horses, preparing them physically for a life of racing.

BUT, three decades of research conducted by Professor Brian Nielsen of Michigan State University and his team and students is telling us, definitively, that we have got it all wrong and that speed is essential for bone health!

Professor Nielsen has recently published a paper reviewing three decades of research into making bones stronger and reducing bone injuries in racehorses.

The most important message from the paper is that confinement to a stable and long periods of slow work reduce bone mass. This then increases the risk of bone injury and bone fracture when fast work and racing begins.

Instead of the traditional conditioning methods that have been used to date, Professor Nielsen recommends short bursts of speed be introduced into a racehorse’s conditioning program early to strengthen bone and reduce the risk of injury or fracture.

Major findings

As a brief overview, the major findings presented by Professor Nielsen in this paper include:

Racing quarterhorses

In a study designed to determine the effect of silicon on bone strength in racing quarterhorses, it was observed that the radiographic bone aluminium equivalences (RBAE; used as an estimate of bone mineral content) had decreased by day 62 (8.8 weeks) of traditional training (no speed early in training). So despite being in training, the horses were losing bone mass.

Most bone related injuries occurred from days 60 to 120 when bone mass was at its lowest.

AND racing started in week 9. So at the point in time when bone was weakest, horses started to race. The combination of weak bone and high speed gave rise to the highest injury rates.

Once horses started to race, RBAE and therefore bone mineral content started to increase again.

In two follow up studies designed to look at the effect of calcium and phosphorous on bone mineral density it was noted that bone loss was greater in horses with longer periods of stall confinement.

Arabian Yearlings

Professor Nielsen and his team were starting to suspect that it was in fact the stall confinement that was leading to bone loss, so they ran a study with 16 Arabian yearlings.

These horses were all initially kept at pasture together. For the study, half remained at pasture while the other half were brought into stables and given one hour of walking exercise per day.

By just day 28 (4 weeks) of this study, the RBAE (bone density) of the stabled horses had decreased and remained low for the 20 week study. Even 8 weeks of race training (starting in week 12 of the study) where horses did 8 weeks of slow racetrack training did not increase bone mass!

Professor Nielsen concluded at this point that with this management style of extended periods of confinement to stables, without any high speed work or access to free galloping at pasture being common in young racehorses, it was likely the cause for high injury rates in young horses managed in this fashion.

Mature horses on high calcium diets

At the same time as this study, a second study was running that used mature horses that were fit and not previously confined in stalls. They took 11 of these horses and confined them to stables for 12 weeks with 2 x 30 minute periods of mechanical walker exercise per day and dietary calcium at twice the recommended NRC 1997 intake. The confined horses lost bone mass.

Weanlings

Following on from these studies, a study in 3 groups of weanlings who were housed either 100% of their time at pasture, 50% pasture 50% stable or 100% of their time in a stable showed that both groups with access to pasture (and therefore the freedom to gallop) had the greatest increases in bone mass as they grew.

A year after the stabled weanlings were returned to pasture they showed the same bone mass as the weanlings who had had access to pasture turnout during the study, indicating that young horses can rebuild bone mass when given the opportunity for high speed exercise.

Exercised weanlings

Then to assess the impact of high speed exercise, another weanling study was conducted where horses were either confined with no exercise or confined with a daily 82 meter sprint,  5 days per week for 8 weeks.

This study showed that the weanlings that were sprinted had increased bone mineral density and altered bone geometry.

Professor Nielsen and his research team then began to question whether this frequency of sprinting was needed to bring about the positive changes?! Would less exercise have the same effect?

Bull calves

At this point they conducted a study in bull calves, with calves either being confined with no exercise or doing a 71 meter sprint, once, three or five times a week. At the conclusion of the study all calves were humanely euthanized, and bone strength parameters were measured.

All exercised groups had greater dorsal cortical widths and the fracture force needed to break the bones was greater for all exercised groups compared to the calves doing no exercise.

And amazingly, there was no difference between exercised groups, meaning calves doing one 71 meter sprint per week gained the same benefits in bone strength as did the calves sprinting 5 times per week!

Sprinting once per week produced over 20% increase to fracture force and demonstrated clearly how few strides at speed are needed to improve bone strength and how damaging confinement without the opportunity for exercise at speed is to skeletal health.

Old versus new thinking

Where horse owners and trainers often get caught up is that we believe that large amounts or long periods of ‘slow work’ will help to condition bone. But research is showing clearly now that bone is responding to the amount it bends (the extent of mechanical load / the speed of the exercise) as opposed to the number of times it is bent.

In other words, short periods of sprinting that put the bone under high mechanical load are effective at increasing bone strength while long periods of slow work doesn’t increase bone strength.

Lots of slow work doesn’t increase bone density

In a study that demonstrated clearly that lots of slow work doesn’t increase bone density, eleven 2 year old arabians were divided into two groups.

The first group was kept at pasture but exercised on a high-speed treadmill at the walk, trot and canter, building up work gradually over 90 days to being capable of completing 60 km endurance tests.

Then for a further 12 weeks the horses were kept in dry lots, exercised twice a week for 45 minutes at a walk and trot and ‘raced’ over 60 km every 3 weeks. But their speed never exceeded a canter of 8 m/s. These horses were FIT! Any covering a LOT of km.

The second group were kept at pasture with no forced exercise.

One would expect that the horses doing large amounts of exercise would have had an increase in bone density. But the results of this study showed no differences in bone density between the exercised and non-exercised groups. Meaning the long periods of slow exercise did nothing to strengthen bone.

A need for speed

Professor Nielsen makes the very clear conclusion, based on research conducted over 30 years, that confinement to a stable without access to exercise at speed weakens bone. And that long periods of ‘slow work’ conducted at the walk, trot and canter does nothing to strengthen bone.

The common practice of bringing young racehorses into work, confining them to stables and putting them into extended periods of slow work will only serve to weaken the bone and increase their risk of bone injury and bone fracture once speed is introduced to their exercise program.

Tiny need for speed

It has also been demonstrated that it only takes a small amount of exercise at high speed to bend the bone enough to then stimulate it to strengthen. But failure to provide this very small amount of exercise at speed will put young horses at an increased risk of bone injury.

In personal communications with Professor Nielsen, he indicated that one to two short sprints per week, where young horses are asked to gallop, and then as soon as they hit galloping speed asked to slow down again (i.e. a very short sprint) would be enough to positively influence bone strength and reduce the risk of bone injury and bone fracture.

This exercise needs to be introduced into an exercise regime as soon as it is safe for both the horse and rider.

Alternatively horses can be given access to free exercise and allowed to gallop at pasture when it is safe and practical to do so!

More informaton

The information in this article is a summary from the scientific journal paper:

Nielsen, B.D., A Review of Three Decades of Research Dedicated to Making Equine Bones Stronger: Implications for Horses and Humans. Animals 2023. 13(5):789.

The paper is open source and available here: https://www.mdpi.com/2076-2615/13/5/789

I highly recommend reading it in its entirety.

You can also view a presentation of Prof Nielsen presenting this research here: https://www.youtube.com/watch?v=IdtHnRqZo4E