Typically in American English the statement would be "a cow is a useful animal" - the first sound in useful is close enough to a consonant that most individuals will use "a" rather than "an".
It depends on what you need the animal for. You can ride both, and you can get milk from both, and you can show both, however, horses are better for riding and cows are better for milking and while you could ride a cow, it is definitely not a good animal to ride, unless you are into buckin' bulls. So, if you want milk/beef, a cow would be more useful. If you want an animal to ride and to compete on, a horse would be more useful.
Cow is a herbivorous animal.
No cow is not an wild animal
Yes it is an animal.
A bull is a male version a female cow is a COW
The animal that cows is a cow
they give milk
we use cow to get milk
Zeus's "cow-bride" was Io.
Cow is a good example of animal with four nipples for breast feeding.
From cultures where the cow is a sacred animal.
Cow.