Q. Why does my horse lick the hitching post, and my hands, and my jacket? She is fed grass hay and has access to a salt and a mineral block, which she uses regularly. Is she missing something in her diet, or is she just an odd-ball?
Regular eating of non-food items such as wood or dirt may suggest there is something deficient in the diet. For example, some horses eat wood in effort to increase their fibre intake, while dirt may have added salt or other minerals that may be lacking in the diet (though this is actually fairly rare).
With a diet based on forage and supplemented with salt and minerals, I wouldn’t think deficiency is the case, but you may consider having your hay tested and the whole diet evaluated by a nutritionist, just in case. Additionally, over the winter, you should consider supplementing with vitamin A, D and E, as it sounds like you do not offer any kinds of commercial feed that are supplemented with these.
Often, when horses pick up oral behaviours it may mean they are bored, don’t have enough forage, have some kind of gastric issue or want a companion. From what you describe, and because she will also go for your body and hands, I wonder if she is looking to do some mutual grooming? Of course, you might also have some taste that she likes, maybe perhaps especially in the summer if you’re extra salty?
Once you rule out nutrition issues or boredom, the only caution I would have would be about splinters. These are more of a problem if she actually eats the wood (and they risk puncturing the stomach), but if she ever goes off her feed you might check her tongue for splinters.