older horse/younger horse-domination

Question
So, we took ownership of our neighbors 10 month old filly.  We have had her at our place for 3 weeks, but have assumed ownership for her about 1 1/2 months ago.  We decided to get her a friend that is a 22 year old gelding.  He is very sweet to humans and he is the one that took on the dominant role.  He has been living with us for only about 4 days and is not terribly dominant.  He does the typical pinning back of the ears and nudging her.  Then later in the day they will be standing right next to each other.  I have two questions... #1 He doesn't let her in their shelter much.  2 of the nights he let her in from about 12am-5am, one night he made her sleep outside, and last night, thankfully he let her in to sleep.  I am unsure if it is he who is not letting her in or if she is just afraid to go in.  I am concerned because she is young still and it's been really cold and snowy out.  Do you think since he lets her in sometimes that eventually it won't be a problem? or will we have to put a temporary wall in there and "lock them in" at night?  I prefer not to do that because I want to give them the freedom to go in and out as they please. The shelter is plenty big for the 2 of them- it is a "run in" type shelter but the entrance is about 7 1/2 feet wide.
#2 The 22 year old is eating the straw that is supposed to be for bedding.  He is a bit overweight and we definitely give him more than enough good quality hay.  Is there anyway to get him to stop eating the straw?  I thought about changing the bedding to shavings but am concerned he will then eat that and that seems to be a worse situation.  Do you think he can be doing this as a nervous habbit? I believe that he has been moved around to different herds/owners in the last few years.  Also, could this be why he sometimes won't let my filly into the shelter with him?  Sorry for such long-winded questions- just trying to be thorough!  Although I rode all the time when I was younger, I am new to horse ownership (can you tell?) I just want to make sure we are doing what we are supposed to be.  Any input would be wonderful :)  Thanks so much!

Answer
Hello Jen,

The straw will not hurt your horse. However, make sure it is free of manure-bugs-etc and provide enough fresh water to keep him from developing impaction.  Make sure his diet is well rounded and if your concerned enough it doesnt hurt to buy a jolly ball and a hay net to give him something to do.  Changing to shavings is a smart idea because the horse will turn his nose to it. The filly is being taught right now who her leader is and this is just a typical herding behavior and should not last more then a week. However, keep your eye on it because once she gets "USED" to not coming in, she wont bother and she will possibly get barn sour on you. If the gelding continues his herding dominant behavior then I would strongly suggest a wall/partition to keep them separate.