I believe cow is just the singular form of cattle, and they can be male or female. Sometimes cow is used colloquially as a synonym for the female designation of heifer. So I suppose both are correct forms.
Actually, male cattle are known as bulls. The female, particularly those who have already birthed calves, are known as cows. Female whales, buffalo and manatees are also known as cows, for example.
[edit on 8/31/0808 by jackinthebox]



