Thick dandruff in mane?

The 17 yo TWH I got a few weeks ago had large, thick "dandruff" in mane. I got her a few weeks ago and her background is that she was rescued in July from a situation where she was basically in the woods starving. Since I got her a few weeks ago, she has been taking supplements from SmartPak -- including Omega Horseshine, SmartHoof Ultra, MegaCell, and some others. So, lots of things to help skin / coat / hair / hoof / etc.

Anyway, about a week ago, I got her main and tail all combed out using Cowboy Magic Detangler. Then, yesterday I noticed that in a line along her mane, she had these huge chunks (nickel and quarter sized) of thick dandruff -- really looked like thick "cradle cap" that babies can get (or a thick scab, but it definitely wasn't a wound scab) and looked like a thick layer of it had detached from her skin and was growing out along her mane. It was gross, but the skin underneath looks good to me -- no crush or flakes (though I am a complete beginner). I combed all of the scabby cruddy stuff out with a comb and gave the area underneath a good massage with a mane / tail "brush" ( Amazon.com: Oster Equine Care Series Mane & Tail... ).

My thought is that the supplements are taking effect causing her mane to grow and the skin underneath to be healthier and thus "shed" off this layer of crud. Does this make sense? I don't really want to add harsh topical anti-fungal / etc. treatments if her body is naturally healing itself, but I am glad to do whatever she needs. Has anyone dealt with this before?

Sounds to me like you're doing exactly the right thing for her. It also sounds like you're spot on as far as why it's all coming out. Keep it up and that should stop soon.

You could scrub her mane with head & shoulders to zap the fungus, or spray it with an anti-fungal horse spray (also used for girth rot etc). I personally think it will probably come back, even after you pick it all off the first time.

As suggested, I would try washing her mane with head & shoulders (or any other dandruff shampoo). If it's "real" dandruff (and not some sort of fungus), it really isn't that uncommon.. horses just like people, can have it.

My mare can have it pretty bad, and she's pretty darn healthy but ugh, it's so unsightly since she's black! I don't really like washing her mane because it strips everything from the hair, making it harder to band.. but if it gets really unsightly I give it a wash with a dandruff shampoo.

If the dandruff is just in the places that you used the spray, I'd be inclined to watch and wait. It's probably a reaction to something in the spray getting on her skin, instead of just being on the hair/mane. My TWH has had a reaction to several grooming products in the past and it makes her have flaky skin - like a sunburn that eventually peels into exactly what you describe as huge flakes of dandruff. Once the skin peels, it loosens and grows out with the hair just as you're describing. At that point, she's healing and there's nothing else you can or need to do (except to remember not to use that product again).

If you watch it and there is anything else going on - e.g. The skin underneath appears to have more peeling, itching, oozing, or anything that looks like there is a fungal or bacterial infection, then you need to treat with a medicated shampoo. Be sure to rinse like crazy...

It makes me so happy when I hear that someone has taken in a rescue and is making their lives so much better! Obviously nothing beats having a vet determine what the problem is but if it is just dandruff I have always heard that you should use Listerine. I've never had the problem myself though and cannot comment on how effective it is.