why do cows have tails?

Question

for communication like dogs?
for balance like cats?
for swatting flies?

???

Answer 1

Do you want to know why, or what for?

Cows have tails because they're chordates. One of the diagnostic characteristics of a chordate is that we have a postanal tail, that is, our skeletal axis is prolonged posteriorly to the anus/cloaca, accompanied by muscles and the nerve cord.
So basically, all chordates have tails, except for the ones that lost them along their evolutionary history (and once a trait is acquired, it takes some evolutionary force to make it disappear, whereas maintaining it is the "easy" thing).

Cows do use their tails for chasing away insects, but also for communication. I'm not sure if there is specific research for this species (Bos taurus), but in other artiodactyls (gazelles, antelopes, etc) the color and position of the tail can be very important signals for other individuals.
Check this publication:
http://ducksrus.bu.edu/~msoren/Stoner.pdf

Answer 2

A cow's tail is too small for balancing like a cat.
I've only seen cows use their tails for swatting flies.

Answer 3

Swatting at flies!

Answer 4

For swatting flies.

Answer 5

For swatting flies.

Answer 6

It was probably a reminiscence of a balancing aid in historical time but now its primary use is to swat those pesky flies!

Answer 7

Flies are attracted to faeces so a swishing tail will keep flies away from the poo hole Keeping everything fly and therefore maggot free

Answer 8

to keep their udders clean and tidy .... swatting flies etc keeps the chance of infection down .... for cow and calf

Answer 9

Far as I know its for keeping flies off its rear end

Answer 10

swatting flies and keeping them out of their 'nether regions'