Are you saying it's too cold to ride because of him? -5 isn't too cold to ride on either F or Celcius. If you mean too cold for you, then I say invest in some thermal under armour and enjoy
The poop eating is I believe due to a nutritional deficiency, and I'm sure other food experts will give better advice than me. My thoughts would be to get a ration balancer.
Does he have a pasture buddy?
If you don't want to ride, then perhaps look at some groundwork exercise to do. Obstacles on the ground, tarpaulins, that kind of thing.