He could pull it off, but again I don't recommend it for showing.
The best thing to do would be this:
**You may want to start after having worked your horse. When he is warmer and his muscles have been working, everything is looser and it may be easier to pull the hair.**
1. Pick up mane thinning shears like these Thinning Shears - Horse.com
And cut the mane straight across making it about 5 1/4" to 5 1/2" root to tip. This is hard to do but it gives the best effect for pulling. You have to force the shears across, but it will leave the hairs uneven (rather than the totally straight line if you were to cut straight across with scissors)
If you can't do that for any reason, cut the mane down to the same length by cutting UP with scissors, directly up into the hair only
until it is all the correct length.
2. Pull the mane with either a pulling comb similar to this Aluminum Pulling Comb with Pick - Horse.com
Or with your hands..both ways demonstrated here in this video if you watch it all the way through.
You can see how she picks out the longer hairs (you want mostly the ones underneath) by grabbing the ends and backcombing. You can also see that you do not want to pull too much hair out at a time. The amount you can pull depends on the horse and the area of the mane. Pay attention to your horse's response. If he seems uncomfortable, try pulling a smaller amount. You can spread the pulling out over several days if it is very thick or if your horse becomes too uncomfortable.
Your goal with pulling of the mane is to shorten
the mane to about 5" whilst keeping it looking natural and to thin
the mane to an even thickness all the way through
, from the withers to the poll. You can test the thickness of the mane as you progress by running your fingers through it and feeling for the thickness of each section of hair, making sure that it feels uniform. It is crucial that it is all totally even (all hair 5" and equal thickness), or else your braids will look funky. To even out the sections that are too thick
, instead of shortening them further when they are the desired length you grab a slightly larger section of hair then part it, letting go of the hairs in the front half and holding onto and pulling the hairs underneath. To shorten sections that are thin
, do not pull. Cut again directly up into the hairs with scissors and cut only small amounts at a time until it is the desired length.
Throughout the entire process, take your time. Every now and then take a few steps back to check your work.
We can pull out the hair of horse's manes without causing pain because they have few nerve endings there, but some horses don't like the feeling of having their neck pulled all over the place. If you or your horse is too uncomfortable with the process, you can invest in something like this:
http://www.amazon.com/Solocomb-Mane-Comb-Standard/dp/B001OE57Q8/ref=sr_1_1?ie=UTF8&s=sporting-goods&qid=1270401896&sr=8-1With a Solocomb, you go through the regular process of picking out which hairs to pull by backcombing the hairs with the Solocomb, then run it to the top of the hairs that are being shortened and squeeze the handle to bring down a blade that cuts the hairs at the top.
This way tends to not look quite as natural, but it works if you can not pull the mane.
It does take a bit of effort to get this all down. If you know anybody who pulls their horse's manes (everyone who shows with braided manes does) you can ask them to help you with it. Sometimes you can even hire someone to do it for you, but I find it's best to do it yourself.
You definitely do not want to roach in this case. The mane will not grow back in evenly as you would think, but even if it did or it was cut to be even, it would still be too thick and too uneven for braids. No matter what you do, the mane will need to be pulled.
Good luck =)