I justove how complicated logistic gets even with the simplest stuff.
“One thing is missing for this army, however: spare horses. A knight does not ride to battle with a single horse, but rather with several. The war-horse is a specialized creature, bred large to support the weight of a knight in armor; they are not endurance runners. So a knight would ride to battle on a smaller, cheaper riding horse. This also, of course, spares the really expensive asset: a good war horse could cost vastly more than a basic riding horse (check out some comparative prices here). A third horse would be required to carry baggage – the riding horse can’t support more weight (it has the rider) and the war horse, again, ought to be spared for the fight. Rohan’s army of 6,000 riders should thus be marshaling out of Dunharrow with more than 18,000 horses.”
https://acoup.blog/2019/05/31/collections-the-siege-of-gondor-part-iv-the-cavalry-arrives/