I’ve solved one issue that pretty much makes the animations look good now. It was an error in how I skinned the rig; some joints really didn’t work well in the position I put them, so I rearranged them and only ask what is sensible of the joint (like an ankle just rotates). It is true that you can do weird things with joints going way out of normal line in SL animations but in this case, paying attention to the norms made a difference.
The only thing that I don’t quite get is the hip animation. It seems to be going in different directions than I tell it to in Maya. I’ve tried re-orienting the model which made no difference, and now I’m experimenting with moving it in non-intuitive ways to see if I can ‘fool’ it into going the right direction.
Moving the hip will be important for various animations like the horse rearing up, or even just the sway in the walk. So I’ll keep working on that part, but the rest of the bodyparts are animating nicely.