Don't speak like that about your mother in law ? 

And why Cows ? What privilege do they deserve ?

Why not People Catcher ?

Or would that have seemed too gory or suggestive

And in any case the device was not set up to catch cows at all, but deflect them.

And why not sheep ?

Because they are thought to be less valuable ?

There is a suggestion from this 1930's picture of one fitted to a car that the cow catcher 
was for clearing hobo's and other rif raff from spoiling the workings of the car.

And clearly Capitalist designers continued with this though 
when metal bumbers were fitted to cars.

You have noticed these have been quietly dropped as a car accessory.

Was it just to save costs or a more subtle reason.

We can't treat the plebs as cows anymore.

So that's it ?

Cows are female and a Bull Catcher sounds more indelicate or that bulls and men 
are more likely to get out of the way of the oncoming tram or train and women are not ?

so Cowcatcher is highly discriminatory against the female sex ?

Not at all - its a play on words to describe a safety first measure and only a pun 
if taken to be.