I'm daydreaming about being done with school and internship and getting to do more fun things with my horse. There is a 15-mile ride, on rolling Vermont hills, in late April. My horse is a 23-yo Arab -- on 24/7 turnout with plenty of room but it's flat, and she's been in no work since last Fall due to my schedule. The conditioning regimens tend to say it takes three months and lots of miles to get a horse from pasture ornament to safe-for-a-hilly-15-mile-ride. That is not going to happen; my schedule is crazy until April and the footing on local trails isn't safe in the winter and I can't risk riding local roads until car drivers can see over the snowbanks. My horse definitely has the heart and interest to walk out of the paddock and power down 15 miles, but I don't want to injure a 23-yo horse. We don't want to be competitive; we just want to do it as a pleasure ride. Her 3-seasons fitness level is that of a backyard pleasure horse, with a basic dressage lesson a few times a month and say 45 minutes of ringwork a few times a week and trail rides of 5 or so miles once or twice a week, with the occasional longer pleasure ride thrown in. At that level, she is "happy-tired" after a 15-mile ride, but not empty.
My horse loves trails, loves to work, has a good mind, and is in.... ahem.... robust weight as we head toward the last stretch of winter. Her topline muscling is gone, though. We just started up with lessons again and she is stiff at first, but warms up out of it, and I just re-started her IV joint lube and that will make a big difference once she's finished the loading protocol.
What do others think about the risk of 15 miles W/T/C on rolling hills, after say one month of long slow conditioning, for a healthy pasture-fit 23-yo Arab?
I would think that would be ok, as long as you're planning to ride conservatively, as you said.
My Arab is 18, and I find that he holds his fitness pretty well over the winter on 24/7 turnout. I usually can't ride much over the winter due to weather, shorter daylight hours, and my work schedule. Two years ago, when we had all that snow and ice, I pulled him out of the field in early March after 6 weeks of not being ridden at all and 2 months of light riding before that, and he was fit enough after 3 weeks to do a conservative 30 with no problems.
It doesn't sound totally unreasonable, and you have stated most of the potential issues, but there are couple of factors I would consider:
How emotional is your horse? If being in company makes her competitive, you may find it more difficult to keep to your conservative plan.
What is the terrain like? Fifteen miles on rolling hills is every different from a steady steep climb followed by a long descent. If this is the trail ride at an endurance ride, ask the ride manager - if not, ask someone local.
What is your plan for the ride season and how does this event fit into it?
Keep in mind that even if you have to sign up for the ride in advance, you always have options - training and preparing for the event will give you a goal, and if your horse is telling you she is not ready, you can always wait for the next one.