Hold keyframes are, by their nature, abrupt. A hold keyframe prevents tweening, where After Effects moves smoothly between values.
In your particular example, though, I would say that the keyframes are not the issue. If you want a smooth transition between those two states of the deer's head, you'll need to draw/create more - that's just too big of a change to smoothly animate between, no matter what keyframe types you're using. Start with something halfway between those two extremes - smooth enough? If not, add two more halfway between those, and so on, until you're happy with the way it looks.