This drives Pepper Mill crazy. It’s only the latest in a long line of cartoon “male” cows. There have occasionally been cases where they correctly portrayed cows as female (as with the aforementioned Home on the Range, but they make the cows male about as often, if not more often. I suspect it’s because the artists are mainly male themselves and adhere to the 99% rule referred to above. Female artists wouldn’t do it.
Notice that nobosy ever portrays bulls as female, though.
That would be Birdo. Yoshi is as straight as can be. Birdo is the one with the sexual identification issues.
I used to live near a goat dairy, where my girlfriend at the time worked as a, um, milkmaid, I guess you could call it. The farm manager was a very funny guy. Groups of schoolkids would sometimes come on class trips. I overheard the following exchange:
Child [pointing at a goat in the milking pen]: The ones with beards are boys.
Farmer: No, all the goats being milked are girls.
Child: What to get when you milk a boy goat?
Farmer: A friend for life.
But the dictionary has cow as either sex any age domesticated bovine. If you’re not sure of the sex and you see a domesticated bovine, and there’s no singular of cattle, you have to call it something. 
Trust me, you’d never be unsure about its sex.
OK, say I am flying in a plane and looking down on a single bovine in a field. I can’t get a vantage point to check out its goodies. “Oh, look, a __________!”
I guess I would have to go with “Oh, look, a domesticated bovine!”
Bingo!
Look! It’s a future hamburger . Or a beef. I’d love to call it a beef.
Wikipedia tells me that the old terminology, which may still work if your a pedant is to call a single bovine animal of indeterminate gender an “ox”, but in contemporary use, “cow” is ok.
Hey, Yoshi does a fair amount of egg-layin’ in the Mario games as well (Super Mario 64 DS comes to mind).
Just in case there is any doubt whether Barnyard’s protagonist, Otis, is male or female, this L.A.Times article quotes its writer and director referring to Otis as “him.”
At least when our cows do it, it is actually sexual. When one of the cows is in heat, and there is no bull around, the other cows will mount up. They don’t get anywhere, of course.
Mr. Stuff informs me that bulls will also ride one another when no cow-in-heat is around. Never seen that one myself, since we’ve never had more than one bull around.
There is usually a hierarchy, but the only way I’ve ever seen this determined is by butting heads and/or using the horns. (We’ve got only one - a Jersey - that doesn’t have any horns, and I feel kinda bad for her.) Even the calves get into this. Watching two month-old bull calves butt heads to prove who is bigger and stronger is quality entertainment. Heh. Cute spindly little things. 
But Yoshi isn’t a cross-dresser. The manual to Super Mario Bros. 2 claimed that Birdo is a man who wears a bow.
Are you guys sure those are supposed to be udders? Maybe they are multiple penises.
So…Earth cows originally come from Centauri stock?
So, my prediction for the movie is that penises will ensue.
He was supposed to create characters with simple lines? Leaving off the udder would have been a lot simpler. Certainly the pig they show exhibits no genitalia or teats.