The medieval Chinese would occasionally strap a tub of flammable/explosive materials to the back of an ox and send it running towards enemy lines. But I doubt that’s quite what you’re looking for.
Then why not ask why cattle weren’t used for the Pony Express, or steeplechase, or driving other cattle? The simple fact is that cattle, whether domestic or wild simply are not as fast or maneuverable as horses over distances of more than a few hundred yards.
Apparently the Romans did something like this too as a Wunderwaffe against Carthaginian elephants: soak a pig in petrol, light, point in general direction. Between the fire and the horrible screeching (if you’ve ever bothered a pig, you’ll know what I’m talking about), elephants backed off.
I said bothered, not buggered !
In addition to the silly videos, see the International Riding Steer Association
at http://www.ridingsteers1.netfirms.com/ . Their website is a bit quaint, but so is riding steers.
Cows have been bred for meat, and are far more bulky than horses. They would require more fodder, and have far less endurance. I would also guess they are harder to train.
That may be a little too much to ask.
It seems in that case their role in the battle was accidental, since it led to the defeat of the army that had them.
A better example is the Battle of Rancagua during the Chilean War of Independence in October 1814. Bernardo O’Higgins, leader of the revolutionaries, was surrounded by royalist troops and in a desperate situation. He ordered all the animals in town to be rounded up - cattle, horses, mules, pigs, dogs - and stampeded them through the enemy lines, enabling him to escape with a few of his troops.
For a moment I thought this thread was about angry women.
I think this is a topic best addressed by Gary Larson
That’s what I am talking about. Horses don’t really stampede, but bovines do. A bunch of armored cows stampeding at infantry is going to fuck some shit up. Obviously, they aren’t going to be as useful as a screening force or flanking force, but for head on assault? I just can’t believe that Rhinos and Elephants have been tried, but not cows.
What would motivate a herd of cattle to stampede into a mass of infantry? You can’t just point them in the right direction and expect them to go straight into what must look to the bovine eye like a scary, loud, moving wall of spiky things (in some ways horses are dumber than cattle.) Any right thinking cow is going to try to go around such an obstacle, not through it.
Your OP asked about cavalry, which is people mounted on horses (or cows, etc.). Are you inquiring about cavalry, or about a herd of (riderless) cows?
I’m picturing a squad of rodeo clowns attached to every infantry company to divert any bovine menace.
The same way soldiers motivated horses to charge. Proper training and experience. My point is about inbuilt natural abilities. Cows have the inherent behavior to lower their head and gore someone. Horses do not.
With riders, of course.
Endurance, obedience to the rider or owner, training, manuverability, comfort.
And what about war zebras? Wouldn’t a mass of zebras cause your opponents to become distracted and confused? I think it would be a great tactic.
That’s the thing though. If you wanted to abort the charge for some reason (like, say, the enemy’s cavalry has crested the hill right behind you) I’m thinking Bull Cavalry would have issues.
At a guess, I would also think horses have a better top speed, which often matters more than raw charging power/momentum: the peasant’s getting skewered one way or another, but you’re not going to zoom about the battlefield looking for weak spots in a line or do the mounted archery thing on the back of a bull.
When you lose the battle, a fast horse is worth its weight in gold as well obviously 
I would love to see Bull vs. Horse Cavalry. I wonder if the bulls would try to gore the horses.
True, but it isn’t as though the peasants are going to out run the cows.
How can you lose a battle with cow cavalry?
[I might learn how to spell cavalry by the end of this thread.]
Cows? Bah, Bear Cavalry is where it’s at.
Cowvalry.
Zebras have never been domesticated. They are not temperamentally suited (they fight back far too much).
Cows have the even more inherent behavior to run en masse in the other direction when they’re spooked. Herd animals may group together to defend their young or when they greatly outnumber their opponents but usually they just want to move (quickly) somewhere less dangerous. I wouldn’t assume that a cow’s “inherent behavior” is to charge a line of pikes.