Join Date: May 2009
Location: Mid Northern TN
I have not seen Vitamin A or anything really prevent lice, but then, I've only seen a few critters with lice and all of them were poorly cared for. They had poor diets, poor health, and also lice. So I always attributed it to the idea that a well cared for animal isn't going to have lice, because if it did, it would have been treated (sort of the definition of 'well cared for'), whereas the animals that are in poor condition are also poorly cared for, and not treated for lice if they catch it. So then lice spreads, and those animals are often kept in conditions that promote the spread of other diseases as well (limited feeding/water points, potential overcrowding, going though stock sales, etc).
I know people swear that vitamin A will keep lice away, but I honestly can't conceptualize why that would be all by itself. Ie, if you kept a horse in the exact same conditions, feed, etc, but JUST added vitamin A, I doubt it would cure them.