How does Donald Hall use imagery in Names of Horses?

The poem itself is filled with imagery. Examples are provided below.

When you were old and lame, when your shoulders hurt bending to graze,
one October the man, who fed you and kept you, and harnessed you every morning, led you through corn stubble to sandy ground above Eagle Pond,
and dug a hole beside you where you stood shuddering in your skin,
and lay the shotgun's muzzle in the boneless hollow behind your ear,
and fired the slug into your brain, and felled you into your grave,
shoveling sand to cover you, setting goldenrod upright above you,
where by next summer a dent in the ground made your monument.