Obviously, twisting wool horse goods around the agitator in a washing machine filled with hot water is not the best cleaning technique for wool. But you can hand wash most woolen horse items or you can use your washing machine like an oversized salad spinner and let it handle some of the labor. Choosing a cleaning product appropriate for wool is a very important first step. Look for a pH balanced washing product with added emollients that prevent natural fibers like wool or leather from drying, and that is formulated to rinse clean leaving no irritating residues. Avoid regular laundry detergents.
Detergents tend to be very alkaline which is why they lift dirt and clean so well.
However, their harsh pH can dry out the wool, stripping the natural lanolin oils that give wool its soft feel and lustre. Perfumes in laundry products or alkaline residues that don't rinse out completely can also create allergic skin reactions in some horses just as they can in people with sensitive skin. Then next step before you wash any wool saddle pad or blanket is to test in an inconspicuous place to be sure that dyes are not going to bleed. Particularly test reds or any woolens you suspect are made of hand-dyed yarns which may be less stable. Now set the washing machine for the gentlest cycle that provides the least agitation and fill the tub with cold water.