If you’ve got to get up and run within an hour of birth, you’ve got to have the bones for it. Fortunately, horses have them. | Photo: iStock

But researchers are still working to understand the complexities of bone growth in the womb. That’s why van Weeren and colleagues recently completed a study on the topic.

Bone Development 101

The “exercising” and “loading” of bones and their inner grid structure—composed of small beams, the so-called trabeculae—are what make them grow strong and able to support body weight and the forces put upon them, he said. That happens in mature animals and in most young animals that can’t walk just after birth, like dogs, cats, and humans. In those species, that loading happens in the days, weeks, and months after birth, building up to walking and running.

But equids (and other “precocial” species in which the young are relatively mature and mobile from the moment of birth) don’t have time for that. Van Weeren said this is partially because of movements and loading in the uterus, but other reasons remain unclear