In the fitness front, I have a couple of observations. I’ve conditioned a very big WB to be quite fit for the T3d, and a big draft cross running Training. I’ve also volunteered for the T and N 3 day a number of years as I am based at Waredaca.
I’ve seen a lot of heavier novice horses looking exhausted halfway around the cross country course. It’s really hard to watch.
I followed a program adapted from Sally O’Connor’s (now quite old) book about prepping for a long format one star. We reduced the speed and distance numbers by the same ratio that the competition numbers were reduced, if that makes sense.
It’s a 10 week program. What this means is that 10 weeks out your horse is very fit and comfortable for, in your case, novice horse trials on similar terrain to the 3 day, running at the top novice speed.
For 10 weeks you need to be able to ride consistently 5-6 days a week, with a conditioning day every 5 days, and extra walk hacks on as many days as you can manage (so if you have a dressage day, you tack on a 20 minute brisk walk out and about. Every time.).
You will need to ride sometimes in the dark or in the rain. You will want to die of boredom. You will think it is ALL worth it when you cruise around steeplechase and then conquer the hardest xc course you’ve ever done with your horse and he finishes feeling great.
Just as an example, the training level program I used had, at its peak, one conditioning day of a 25 minute trot in terrain with an additional hour long walk hack, and another conditioning day with 4 and 5 minute canter sets, with a minute sprint at prelim speed embedded in some of the sets. Every 5 days I’d be doing one or the other.
It’s an awesome and fun and doable goal, but do your horse a favor and make sure you can find the time to give to him for those last 10 weeks.