What was the first breed of horse?

It's impossible to say definitively what the "first breed" of horse was, because horse evolution is a gradual process that stretches back millions of years.

Here's what we know:

* The earliest horse-like creatures: These were small, dog-sized animals with four toes on each foot. They lived about 55 million years ago in North America.

* Gradual evolution: Over millions of years, these animals gradually evolved into larger, faster animals with more powerful legs and fewer toes. This process was driven by changes in climate and vegetation.

* Modern horses: The first truly modern horses, similar to the ones we know today, appeared around 4 million years ago.

* Domestication: Horses were domesticated around 6,000 years ago in the steppes of Central Asia. This process led to the development of various breeds, but the earliest "breeds" were likely just groups of horses selected for specific traits.

So, there wasn't a single "first breed" of horse. Instead, the story is one of long, slow evolution, with modern breeds arising from many generations of selective breeding after domestication.