when did this sport first take place?
1820s and 1830s
Rodeo
Early rodeo-like affairs of the 1820s and 1830s were informal events in the western United States and northern Mexico with cowboys and "vaqueros" testing their work skills against one another. 
what is dominant white? A.k.a  white spotting -  group of genetically related coat color conditions in the horse, best known for producing an all-white coat. how is this identifed? UNANSWERABLE what is its relation to sabino? It is a group of white spotting patterns in horses that affect the skin and hair. how are these animals domesticated? The clearest evidence of early use of the horse as a means of transport is from chariot burials dated c. 2000 BCE do they have a sleeping pattern? They are able to sleep both standing up and lying down; and are able to enter light sleep by using a "stay apparatus" in their legs, allowing them to doze without collapsing. can you tell me about their skeletal system? Its skeleton averages 205 bones, significant difference from human skeletons is the lack of a collarbone. what is this apparatus you mentioned above? It is a group of ligaments, tendons and muscles which "lock" major joints in the limbs of the horse. in what all sports is this animal used? Show jumping, rodeo, sport hunting, horse racing etc. what is the second one about? It is a competitive equestrian sport that arose out of the working practices of cattle herding in Spain and Mexico. where did it get its name from? From Spanish "rodeo" (meaning "round up") which in turn comes from "rodear" (meaning "go around").
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Rodeo [SEP] History
Many rodeo events were based on the tasks required by cattle ranching. The working cowboy developed skills to fit the needs of the terrain and climate of the American west, and there were many regional variations. The skills required to manage cattle and horses date back to the Spanish traditions of the "vaquero." Early rodeo-like affairs of the 1820s and 1830s were informal events in the western United States and northern Mexico with cowboys and "vaqueros" testing their work skills against one another. Following the American Civil War, rodeo competitions emerged, with the first held in Cheyenne, Wyoming in 1872.