I often get asked what the difference is between Trec and Horse Agility. If one knows very little about either, it's a fair question! Almost the only thing they have in common, though, is the use of obstacles!
Trec is almost exclusively a ridden sport. In competition, it consists of 3 phases, of which the obstacle (PTV) phase is relatively minor. The Control of Paces (CoP) and Orienteering (POR) sections carry more points in the competition and a mistake on one or both of those sections (CoP & POR) usually (although not always) delivers far more penalties than a simple mistake on the obstacle section. Trec obstacles, although they may cause a horse to be wary of them on first encounter, are all designed to simulate hindrances that you may come across whilst out hacking, as such they are predominantly "rustic" in nature and the differences between Levels 1 and 4 are relatively minor: higher, wider, narrower, etc, but not massively so.
Horse Agility is almost exclusively a non-ridden sport (In Hand or Liberty) and there are more parallels between how a Horse Agility course is judged and how a dressage test is judged, than how a Trec obstacle is judged. Horse Agility obstacles are marked out of 10 points, with maximum 5 points allocated for correct completion of the obstacle and maximum 5 marks allocated for the relationship between the horse and handler. Horse Agility is unique in being judged on the relationship between Horse and Handler. Horse Agility obstacles are almost all inspired by Dog Agility obstacles, scaled up for equines. As such, they tend to be far more brightly coloured, more "artificial" looking and have far more "spookiness factor". There is also a different levels system within Horse Agility obstacles, with the degree of difficulty in which the obstacle is to be completed increasing significantly between Starter level and Advanced 1* level. Not only do the obstacles themselves get harder (e.g.longer, narrower, etc), but the level of communication and connection with the equine also has to be much higher. E.g. Horse and handler to walk through an S bend at Starter Level; Horse to back through an S bend at advanced 1* level, while the handler stands at a fixed point and does not move his/ her feet!
What both Trec and Horse Agility obstacles have in common, especially for training purposes, however, is that they are very useful for building your horse's confidence around a variety of obstacles in a variety of situations; they are great for building up trust and communication between horse and handler; and they are great fun! :-D