Do you comb the mane with a brush or mane comb? I was told to always use your fingers to comb out manes and tails as the hairs don't break as easily that way.  I'd also try using hair conditioners (I tend to use human products) as they aren't usually as costly.  As far as supplements, good grain and hay is really the key, but you could check the various catalogs and see what looks good to you. 

   If the mane gets alot of sun (bleaching) it will also make it more brittle.

Sounds like the detangler could be the culprit.  There's another thread about manes that offered some advice and might help you out. My horse has a gorgeous mane and tail and I haven't had to use much conditioner, but you could try some out and see how they work.  It's really alot of trial and error to see what works in your situation.  Sounds like food isn't the problem. 

Some horses manes seem to tangle more easily than others.  I know of one horse who's long mane tends to twirl and his owner struggles with untangling all the time.  She started braiding it, but you can't leave the braids in all the time or it causes other issues.  Good luck

I'm late postin on this but i agree with what some of the others say the detangler here is the culprit. Skip using it and use a conditioner/water spray on mis does the same job pretty much and moisturizes the mane and all instead of drying it out.  This sounds silly but ummm have also used mayonaise straight on the mane and tail once in awhile to give it a deep conditioning. A particularly dry mane and tail literally soak up  the oils in it. Leave it on for about 5-10 minutes then rinse. Works pretty good and keeps things very soft and shiny.( works on very dry human hair too...lol got the idea from my sis ..she's a hairstylist and some of the products they use for very deep moisturizing are basicly mayonaise..) aAnywho laters and good luck.

Lively

MTG by Shapley's is a product that is very oily but many people swear by it. I personally have found the leave in conditioners to be the best. MTG is very greasy, smelly, and seems to attract dirt and debris which gets the tail dirty and dries it out more. My gelding ribbed his tail worse with MTG because of all the dirt it attracted and made him itch.

Another product I absolutely LOVE is "Love That Tail" conditioner. It is a leave in conditioner that is full of moisterizers. You can get it at many tack stores, including State Line Tack. Your hands will be buttery soft after using it - better than any lotion I have ever found.

I fond that the aussie line of products for humans is awsome on horse hair, my TB has a crappy tail that is always tangled and breaks easily, I just use the conditions let it sit a minute and then rinse. His tail feels so soft. I also started using a supplement from Smart pak equine (which I love, just peel on dump no measuring!!!!) it is Gleam and Gain, it helps with coat, mane, tail and even with body fat. It only runs me about 17.00 a month. Plus they have many more to chose from.

Melissa

I was a part of the other thread on manes. :) I've never used cowboy majik but if it has silicone in it, that's probably part of the problem. Which brand of feed are you using? It sounds like you have him on a good feed program but some feeds are better than others.

My horses have the same "natty dred-locks" problem that Dunoir described (long manes, they love to roll around in the dirt) so, what did I do? I use Afro Sheen! Actually, I use African Pride "Miracle Gro". I think that's the name. (check out that other thread, we really went into a lot of detail.) but It's definately African Pride. This stuff really works great! Gives it sheen and detangles but one thing I found out is that in cold weather it gets clumpy...BUT when the weather warms up the sheen and the health really comes out. It's a great conditioner. Just dont be discouraged if the weather turns cold and they have a waxy build up. It's actually a good protector from the elements.

I also put about 1/4 cup of vegetable oil or safflower oil w/ Vitamin E in their feed (the Safflower is made by Hollywood brands, it's hard to find but REALLY works.) Just makes sure whatever oil you use doesnt contain canola. ;)

Good luck. A great mane is a pleasure. Those horse products stink , the are full of silicone and ridiculously expensive. It's amazing what you can find in the African american section! And the savings are to die for. ;) (They take us horse owners for such suckers. And we are.)