There seems to be a bit of confusion between the type of deer called fallow deer, which leeneia said is the deer with the scientific name Dama dama. It's just a name for that type of deer.

The word "fallow" in relation to a field is a different concept.

It's obvious that female fallow deer can be pregnant otherwise that type of deer would be extinct so there is not much point discussing how the fallow deer in the song can or cannot be pregnant based on the concept of "fallow" in relation to fallow fields. Apples & oranges.

I've loved this song since I first heard it in high school music class. I especially love the melody, and the whole story of the knight lying slain under his shield.

I always thought it was like a fairy tale or fantasy story and then after studying Middle English literature I started to think it was like a mediaeval courtly love song with a fantastical theme, which honours true love.

I guess I always thought that somehow the knight's true love, i.e. his leman, had been changed magically into a deer for some reason but she found him after he was killed and looked after him and then died herself because of the physical exertion in carrying him and burying him.

The melody contributes to the magical nature of the story, in my opinion. To me it is ethereal and haunting and it conjures times in the distant misty past.