What does mad cow disease do to cows?

Makes them Mad by deteriorating the nerves in the brain.

The Mad Cow Disease is a Prion Illness. A Prion is a protein or part of a protein.

As of such, the "disease" is not alive, much the same as a virus, of which is neither alive.

A Bacteria is a living tiny creature with the ability to multiply by itself when given nutrient's.

A Virus is in need of a host where it tricks its host (a living cell) to create copies of itself.

A Prion illness is more a sort of chemical illness that does its work chemically.

This particular Prion Illness eat away chemically on fat-tissue and creates chemical copies of itself in the process.

All nerve tissue is isolated by a thin layer of fat. These "nasty" prions "eat" away this protective layer in a chemical reaction causing nerves to shortcut. All animals have a brain where there is a lot of nerves. This is where the disease causes the most devastating effect because the brain is actually being shortcut. Electrical impulses in the brain does no longer work the way they are intended.

This causes a cow (or any other affected animal, even humans) to act strangely and lose control of its ability to do normal things, such as walk and think straight. An infected cow would act "mad," which sometimes means mentally ill, of which it actually is in the worst possible context when the brain deteriorate...

A bit crude explanation but to the point.

Note.

It works the same way in all affected animals, humans included.