Amount of conditioning before the first ride

Excellent point. The ligaments and bone take a lot longer to develop - in endurance, we say that it takes 3 years to develop a full endurance horse. However, you can still do rides during that time - just take it conservatively. Don't try to race, and don't enter every single ride. I'm starting a new endurance horse this year and hoping to do about 4 to 6 50's on her, no more than one per month.

My second-year horse I plan to do about twice as much with. If all goes well, we're really going to hit the endurance trail next year and load the miles on!

However, most people just looking to get into "endurance" can do so within a few months if they take it easy and enter LD's (or even 50's), give the horse enough time off and space out their rides, and don't turn it into a race.

The background plays a huge role as well - Just as endurance horses conditioned in the past come back to being race-ready more quickly than new horses, I would think it would be a much shorter "conditioning" period for an eventer!

And when you get your horse conditioned up to 50's and are going to at least 2 rides a month (1 every two weeks), you can almost just count the actual rides as conditioning as well with only a little conditioning here and there in between, if at all. There is nothing wrong with coasting along for a year at that pace and finishing in the middle of the pack - it is what a lot of folks do once they get the cardio built up - then they coast for a year and just let the ligs and tendons catch up. Then they are ready to progress the following year with longer rides or multi-days.

I would actually say the same about doing a ride every 3-4 weeks, especially if you're doing multi-days. I try to give my horses a week off for ever 25 miles within one ride (so I'd give one week off for an LD, two weeks off for a 50, but the rides wouldn't necessarily add up - it'd still be two weeks off if I did two 50's) and then I go pretty light the week before the ride. If I was doing a 50 every 3 weeks, that'd mean I really didn't condition in between, but rather just when for a light trail ride or two.

Im new to endurance and wanting to get into it. I chose my 14.2 hand appy qh mare (You can view her under horse comformation critique 'comformation? Endurance prospect?' and tell me what you think) We started conditioning today and im weondering if I can do arena work(a half hour usually) in the morning and a long ride about 3 miles in the evening(will begin to increase later). This is what we did often last year, because its to muddy from frost in the morning to ride on my hill and by evening its usually dried out.
Also I was wondering how you know how many miles you have done. I can estimate 3 pretty good because that's how many miles I walk my 5 dogs every day.

Most use a gps to calculate speed and distance.. But ummmm 3 miles isnt even a warm up.
Nothing wrong with round pen and arena work to improve the mental game, should be one of your weekly training sessions. The other 2 need to be steady moving for a couple hours. If your horse can only walk just walk for two hours, then add a bit of trotting, working up to holding a trot for two hours.

FInd the book Endurance 101, really good book written in a lighthearted manner, can get it at Amazon or on kindle or Barnes and nobel

You can and should do some arena work, but the trail work should probably go longer, so you can do the trail twice to three times if that is the only trail you have. A great way to know how far you are going is the app "Map My Walk" or "Map My Ride" available on a smart phone. It will tell you length, elevation gain and speed (pending that you have good reception and get a signal the whole way around). You really want to do long, slow walks for the first 2 months or so, like 10-15 miles. When I am conditioning I try to ride 3X a week (and sometimes it doesn't work out for me because children are like that!). Then move up to walk/trot, then trot, and hopefully you will have found some more trails by then and it won't be so boring for you and your horse. Horses get bored, too! We have a very hilly trail near our house and my mare and I do it often, but she knows every single part, so I try to make it interesting by asking her to perform tasks or do things wonky so she isn't super bored.

Ok! Ya ill start riding at 3 then and finish when the sun goes down (Around 5-5:30 here) Then and ill slowly build up. I try to do a half hour of arena work 3-4 times a week with my horses, with all different sorts of thinks from small jumping polls to doing different figures and doing leg work(Reining off legs) I like to keep my horses very sharp and responding well for when we do trail riding.

Arena work and other cross-training activities are excellent for conditioning if you keep a sustained trot at least for an hour or so. Many of the endurance ladies I know actually do drill team together and once tracked 8 miles during one practice. Their horses are in excellent shape for all this practice. Long walks can actually be very difficult on your horse's back not to mention tiring for you. I wouldn't really ever do a 10-15 mile walk unless I was doing a back-country day ride. I haven't ever done one for endurance. Rather, I brought my horse up to speed from being a stalled horse exercised on a hot walker by riding him in the arena and working on fundamentals, often at a good trot or lope (approx. 2 months). When I started conditioning, I started at 5 miles of a working trot (8-9mph) and then steadily added distance when he was ready (after 2 months of this, he was ready for his first LD).

This is great info! I am currently trying to get my Haflinger to do LD's, but am worried about the conditioning! Just going to take our time and see where we can get!