^ magic cushion is more so to take down inflammation in cases such as laminitis or a bruised sole. I’d continue with the epson salt poultice.
As for prevention, I’d look at two main things: (1) balance and quality of hoof trim and (2) Diet.
An unbalanced hoof trim could certainly exacerbate any predispositions towards abscesses, just as overgrowth could. I think more frequent trimming cycles could help for sure!
Now for diet, it is great that you are considering a hoof supplement; however, the supplement will only go as far as the nutrition is balanced - it could actually be counter productive in certain circumstances.
One mineral deficiency that is actually associated with increased risk of abcess’ is Copper (Cu). I mention this because I’ve found many hoof supplements either lack it or don’t have enough of it. Copper is necessary for a key enzyme (lysyl oxidase) which catalyzes the cross-linking of collagen, and thus is vital for the strength and rigidity of the outer hoof wall’s fully cornified cells and is an important component of antioxidant enzymes that protect cell membranes. The resulting tight white line connection is what helps prevent bacteria from getting in, otherwise you’d have a horse more prone to things like thrush, abcess’ and white line disease.
Zinc, on the other hand, seems to more often be added to supplements and is needed to maintain hoof quality by being involved in synthesizing keritin (keritinization).
However, you won’t necessarily get an effect by just adding the minerals because each mineral’s absorbance is affected by other trace minerals. Specifically, copper interacts with Zinc (Zn) and Iron (Fe) too, so these minerals need to be in balanced to be absorbed properly! An excess of Zn or Fe will interfere with Copper absorption and vice versa.
These minerals need to be approximately at a ratio of 1 Cu: 4 Zn: 4 Fe. It has been recommended that Zn should be around 400mg per day, so the horse needs 100mg of Cu per day and horses are often within excess Fe. Nutritional Fe deficiency is rather rare and usually anemia is a result of other issues such as chronic inflammation or bleeding. Even blood tests can mix up Cu deficiency vs Fe deficiency. A false positive blood ferritin (falsely low iron) can even occur with low copper because Fe uses a copper dependent enzyme to convert itself to its ferric state, which makes iron absorb better. For those reasons, it is now being recommended more to feed little to no iron, unless it is otherwise needed.
So, what I do recommend is testing your hay and then adding those values to what is being fed in your horse’s grain, then you can start to see how much of which minerals and vitamins you’ll need to add. Otherwise, you could just do the calculations for feed to see how much Cu, Zn and Fe your horse is currently getting there.