Of the twelve Chinese zodiac animals, some are translated into English as various names, such as 羊 as "sheep", "goat" or "ram", 鸡 as "rooster" or "hen", and when a year falls on such a zodiac animal, there is invariably a debate as to which English word is the best fit. Other animals are much less debated. For instance, nowadays 牛 is almost always translated as "ox".
So another question arises, Why is "ox" preferred to, say, "bull", "cow", "buffalo", or "cattle"? In fact, such translations did exist, but they gradually died out over the past decades, specifically since 1960's or 1970's according to Google Ngram. The reason for "ox" to eventually come to the top is not easy to explain, as is the case with many things in human languages. Let's break up the question a little bit. To be precise, an ox is a castrated male cattle, a bull is an uncastrated one, and a cow is a female. I think the reason why the word "cow" is not chosen, in spite of its higher usage frequency, is that in the western zodiac, there is the Taurus, which is male, and that word and its referent probably had some influence on the early choice of word for the Chinese zodiac animal 牛. Next, let's analyze the choice between "ox" and "bull". According to an Internet user who answered the question I posted to a Facebook group, an ox is a bovine trained as a draft animal, as stated on Wikipedia. Similarly, a 牛 in the mainstream traditional Chinese culture is also a draft animal, not one as the source for food (beef, milk, etc.). In this sense, English "ox" is the more appropriate translation than "bull".
Back in 2015, I blogged about the English word for 羊 as the Chinese zodiac animal, and I proposed the idea that to eliminate the ambiguity in the Chinese word or character, we simply find the biological name at the lowest level in taxonomy under which the species the various English names refer to are. For example, a sheep belongs to the genus ovis, which belongs to the subfamily caprinae, and a goat belong to genus capra, which belongs to subfamily caprinae. Therefore, the best word to translate 羊 is caprinae. Well, it is best only if we can ignore the ignorance of the general public. But generally that's not a very good idea. Fortunately, in the case of 牛, the word "cattle" seems to cover both "ox", "bull", "cow" or even "buffalo", and "cattle" happens to be a common word that even an ignorant John Doe knows the meaning of. So I think "cattle" is the best translation for 牛. But it's too late to promote this because the English-speaking people have already been saying "ox" for Chinese 牛 for 50+ years.