The speaker looks at a cow standing in a field and finds it strangely remote. Calling it "like another country" suggests something self-contained and foreign, a place you can see but never enter. The cow is so still that it won't even twitch to shake off a fly, and that stillness is what holds the speaker's attention.
The last couplet is the most puzzling. The speaker says that where they "see air," the cow "sits with the dead." One way to read it is that the cow's calm seems to belong to another realm, as though it has settled into a quiet the living can't reach. The speaker looks at the empty space around the animal and senses something absent there, or something that has passed on.
The mood is hushed, a little eerie, and oddly respectful. The speaker doesn't judge the cow or explain it. They just watch, and the short lines leave plenty of silence around each image, much like the field itself.