airway inflammation allergies ambassador ammonia behaviour breathing breathless colic comfortstall dressage EGUS elderly equine asthma equine behaviour equine health Equine nutrition eventing fatigue feed foals forage forager geriatric grazing hay steaming hay storage Haygain horse coughing hydration IAD joint health laminitis nutrition performance physiotherapy rehabilitation centre research respiratory disease senior slow feeding soaked hay soaking hay stable flooring stabling steamed hay testimonial veterinarian WEG winter