The Kine of Araw were descended from the even greater kine (cattle) of Oromë the Hunter, who was known to be the master of beasts and birds. As Oromë was chosen to lead the Elves on the Great Journey, he might have intentionally (or accidentally) left his livestock in the East.
They presumably lived in the areas immediately adjacent to the Sea of Helcar, relocating to their present location around the Sea of Rhûn when that great ocean dried up.
Vorondil the Steward of Gondor ventured to the Far East and hunted one such beast, utilizing its great horns to craft the exquisite Horn of Gondor. For the lengthy years afterward, it became an heirloom of Gondor's stewards, handing it down to their oldest son for innumerable generations.
However, its doom drew ever nearer, just as Sauron’s shadow returned from the depths of the East. During the War of the Ring it was carried by Boromir, son of Denethor. It was only when Boromir was assailed by hundreds of Uruk-hai, that the horn was eventually broken. The Uruk scimitars and broadswords clove the great horn in two, rendering it useless. After being presented to his grieving (and insane) father, it was buried with him.
According to Appendix A of The Lord of the Rings, the Kine of Araw were far larger and splendid than common, earthly cattle (like Old Bessie). Their hides were a gleaming pallid white that reflected the sun rising from the Gates of Morning in the east.
The horns attached to their gargantuan bodies were colossal in size, giving the kine an air of grandeur. While nobody knows what the kine really looked like, their size and scant description that we possess may give them an appearance similar to the real-life Texas Longhorn.
There are certain parallels between the Kine and the real-world bovids such as Aurochs. The Aurochs is considered to be the ancestor of modern cattle; they were large, dangerous animals with great horns living across North Africa, Europe, and most of Asia. The Aurochs was driven to extinction in the 1600s by heavy hunting, especially by royal families across Europe.
Certain population of Wild Yaks in China, and some of Bisons in America are known to possess golden and white furs. Wild Yaks and American and European Bisons are amongst the largest surviving bovids and surpassing extinct Aurochs.
In Europe, there once was Water Buffalos until arrival of humanity, and there is an ongoing project to rewind extant relative to Europe, so as the American Bison reintroductions to Asia and European Bison reintroductions to various areas of Europe and Russia including British Isles.
Similar to the Kine of Araw and other animals of Arda, many of prehistoric terrestrial animals were much bigger than today's descendants. Of all wild cattles, Giant Bison and Pelorovis were the largests both in terms of bodies and horns.
Other bovid species such as Gaurs, other members of Buffalos, Elands, and extinct and surviving kins of Giraffe are also noted with their size and horns, but these are more adapted to warmer climate unlike the Kine of Araw. Bigger relatives of Muskox also inhabitted Europe, but their bodies were covered with furs unlike the Kine.
Kine is an archaic English word, meaning "cattle." As Tolkien was deeply fluent in Old English, Welsh, and Scottish, he would have used the term rather than a more modern one to better suit the medieval feel of the Lord of the Rings.