http://www.bmezine.com/tattoo/A50414/high/bmegl050199.jpg
Here is a question for all the ladies out there:
Would anyone of you mark yourself with a tattoo saying you are a "cow", or perhaps a "heifer"?
If your answer is "no", then why would you do it in another language that you probably don't fully understand?
Granted, there are cultures that do regard highly of the animal, but it is doubtful in the Western world. Just think when is the last time some guy could start a conversation by complementing a woman's cow-like features?
The character 牛 is a general term used for any member of the Bovinae family. If there is not a secondary character to specify, then 牛 on a female could be interpreted as "cow".
Update: Correctly Done and it means "pig".
http://www.bmezine.com/tattoo/A50429/high/bmegl057082.jpg