What passing-bells for these who die as cattle? (1)
Being killed like an animal isn't anyone's idea of glory, and this line makes sure that we don't approach the idea of dying in war with any undue excitement. Any patriotic idea these soldiers might have had about how heroic it is to die for their country is totally undercut by this simile. There's the suggestion, through the comparison to cattle, that the soldiers are trapped and at the mercy of others. It doesn't leave much hope of escaping death. How many cattle have you heard of escaping from the slaughterhouse?
Can patter out their hasty orisons. (4)
That word "hasty," plus the haphazardness of "patter," relates to us the suddenness of death on the battlefield. Not only is death fairly certain, but it doesn't necessarily announce itself far in advance. It's not stately, heroic, or glory-filled. It's quick and dirty.
And bugles calling for them from sad shires. (8)
This is the first time the poem reaches out beyond the death of the soldiers to mention the suffering it causes others: relatives, neighbors, and so on. Those "sad shires" really are pitiful, calling for their dead young men. The only way they seem to get them back is for a funeral.
And each slow dusk a drawing-down of blinds. (14)
This quiet, beautiful image points to death in about a bazillion ways. Dusk and drawn blinds are both a sort of end or closing. Plus, the line even comes at the end of the poem; yep, the poem itself is dead, too. Plus it can be read from the soldiers' perspective, with the onset of dusk standing as the equivalent of pulling down blinds (making it night). Or it can be seen as an image of civilians reacting to the death of soldiers, either to keep out the reality of it, or to shut out the world so they can mourn in their own private ways.