Long Grey Mare lyrics

I've got a long grey mare, she won't let me ride
I got a long grey mare, she won't let me ride
She makes me brush her in the morning
And put her to bed every night

Long grey mare, why can't we be just like before
Long grey mare, why can't we be just like before
We used to ride so hard
Until we just couldn't ride no more

break:

Look at me grey mare, don't I feed you everyday
Look at me grey mare, don't I feed you everyday
But when I dig you with my spud
You turn around the other way

Submitted by Guest

What do you think is the meaning of Long Grey Mare by Fleetwood Mac?