I'm only guessing that Deer is male. He is by himself, bigger than a fawn but smaller than an adult, and has the bouncy gait of a young animal with too much attitude for its size. I'm curious to know if he is interested in the water, interested in the hay, just looking for company (because he's all alone), or if he is just interested in the stranger-girls that are uphill from the garden.
The girls are grazing the garden where the deer like to wander through, so there is plenty of cross-contamination already occurring. There are parasites which can be shared back and forth, and probably plenty of cooties too. Those are known issues. I would rather not actively feed the deer, though.