Why we don’t just go by “12 months” 🐾

You’ll see a lot of advice online (and on kit packaging) that says dogs can start canicross at 12 months. It’s not wrong exactly, but it’s only part of the picture, and it’s worth explaining why Tailrunners takes a more individual approach.

The 12-month rule comes from limb growth plates — the cartilage at the ends of the long bones that lets your dog’s legs grow. Fair enough. But your dog’s spine has its own set of growth plates too, at each vertebral end plate, and those typically don’t fully close until around 11 months even in an “average” dog — later in a lot of our bigger or slower-maturing breeds. So the spine itself is often still finishing up right around the point people think it’s safe to start pulling.

And if your dog is neutered, that timeline shifts again. Sex hormones are what trigger growth plates to close, so removing the source of those hormones before a dog is mature delays closure — sometimes significantly. A well-known 1991 study (Salmeri et al) found dogs neutered at 7 weeks had growth plates that stayed open considerably longer than intact dogs, and even dogs neutered at 7 months showed delayed closure compared to those left intact. So “my dog is a year old” doesn’t automatically mean “my dog’s growth plates are closed” — if they were neutered young, that clock may have been pushed back without anyone realising.

But bone closure is only step one anyway. Two other things matter just as much before we let a dog into a harness and lead:

Soft tissue development — the muscles, tendons and ligaments that actually stabilise and protect those joints once the bone has stopped growing. Bone can be “closed” on an x-ray while the surrounding soft tissue is still nowhere near strong enough to cope with sustained pulling force, sharp turns, and repetitive impact. That conditioning takes months of appropriate, progressive work — it doesn’t switch on the day the growth plates shut.

Mental maturity — a young dog who’s physically capable of pulling doesn’t always have the impulse control, focus, or judgement to pace themselves, avoid awkward landings, or listen when it matters at speed. That’s as much a part of injury prevention as the physical side.

So when we assess a dog for the sport, we’re not just asking “has this dog turned one?” We’re looking at the whole dog: skeletal maturity for their specific breed, size, and neuter history, how their conditioning is coming along, and whether they’re mentally ready for the demands of running attached to a human at pace. Some dogs are ready a bit later than 12 months. Some need longer still. It’s individual.

“But sled dogs start pulling as puppies…” 🛷

This comes up a lot when we talk about waiting for our canicross dogs — someone points out that mushing kennels have puppies in harness from a few months old, so surely the 12 or 18 month rule is overly cautious?

It’s a fair question, but sled dogs aren’t actually the exception they look like from the outside. A few things are going on:

Gear early, load late. Mushing kennels do introduce collars and harnesses from around 4–5 months, and young pups get walked through commands like gee, haw, and whoa. But that’s familiarisation, not work. The actual convention across mushing is the same as ours: no meaningful drag weight or real pulling on the line until growth plates have closed, generally not before a year, alongside a proper soundness check on hips, knees and gait first. So the harness goes on early, but the load doesn’t.

They’re bred for exactly this job. Sled breeds have been selected for pulling conformation, connective tissue strength, and temperament over many generations. That’s a very different starting point to a Lab, spaniel, or Munsterlander being asked to do a sport their structure wasn’t purpose-built for. It doesn’t remove the growth plate window — but it does mean the dogs, on average, carry more built-in tolerance once conditioning starts.

And the scale is completely different. A working kennel’s “training” for a young dog is gentle team trotting to build fitness and manners. It’s not sprinting flat out against a bungee line, which is what our dogs are doing from their very first canicross session. It’s a much more gradual ramp than the puppy-in-harness photos suggest.

So when you actually dig into it, mushing doesn’t contradict the 12/18-month-plus, whole-dog approach we take — it confirms it. Even the sport built entirely around pulling still waits for the skeleton to be ready before adding real load. The harness might go on early, but the running doesn’t.

If you ever see conflicting advice online, come and ask — happy to talk through where it comes from.