Horses are a part of the taxonomic family Equidae which includes horses, donkeys, zebras. Basically, Equidae can be characterized through their manes, slender legs and stocky body, and hooves.
Equidae can be traced back 55 million years ago to the species called Hyracotherium (Eohippus) which generally looks like the Horse but with one major detail; it was the size of a small dog. Apparently, climate change caused an increase in grassland, the main diet of Equidae, which caused a major increase in its size over generations alongside natural selection. Predecessors to the horse were native to North America before they migrated along a landmass that no longer exists on the Bering Strait which connects North America and Russia. It is believed the horse went west until it was found in Europe. The first humans in North America, known as the Clovis, had tools that were covered in protein residue from Horses so there's a theory that humans caused the extinction of Horses in North America. Fortunately, the horse was reintroduced to the continent by the Spanish in 1519, unfortunately, the Spanish came to colonize :(.
Now the horse is found on every continent of the world except Antarctica and has been bred to fit multiple purposes. There are over 300 breeds of horses, each with different qualities and purposes. For instance, the draft horse, with its large size and endurance, can pull over twice its weight. On the other hand, light horses were bred to be speedy and agile. These are the typical horses you see in races or for casual riding.
Horses can be used to supply blood for diagnostic testing and vaccine development. One company that provides this service is Serum Australis where horses are handled with low stress to maintain trust with the animals. Their blood can be used to detect respiratory infections and venereal diseases and horse serum helped develop the diphtheria vaccine.
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