The latest update on horse deworming is to have your Vet do a fecal exam on each horse. Some horses have a natural defense against parasites and carry a smaller load, others do not. Your Vet can identify which is which for you for a nominal fee. I, personally, like to rotate dewormer chemicals. IF your new horse carries a large amount of parasites it is Possible that you could have an impaction. From your pictures I just think that he has some parasites and has been on a lousy diet of poor hay/and/or somebody counting flakes bc of cost. I count flakes and have been wondering if my horses could lose a little bit of weight.
And, of course, you want to remove manure where your horse eats so that he does not reinjest them. THAT is why people pile up their horse's manure, to create the heat it takes to kill the parasite eggs and larvae.
When it is hot and DRY and when it is cold and DRY you can spread it out and the parasites will die bc of lack of moisture.