When I first reclaimed my pasture, I had woody stems from raspberry bushes that were 6'+. My stems were about the size of a quarter in diameter and maybe 2-3 inches high. And unfortunately, I have no suggestion other than time. When I asked on this forum, pigs came up a bunch. I never went that route and really, after about 6 months, 90% of them were gone or decayed enough that I could just pull them up. I still have a couple that refuse to die, but not enough to enduce me to action.
Can you mow them with a brush hog? Just shortening the canes helps, though it will leave some spiky stubble if they are old canes. Probably wouldn't bother the horses hooves, if they are raspberries.
Woody canes/sprouts of new growth would be more solid and a BAD IDEA to mow, unless you immediately go back to cut the spikes down to the ground. Those would be Punji Sticks like they spike Tigers on in dug out traps. BAD for horse hooves!! I cut my woody growth with hand pruners, so I get them to the ground level on one visit. I can't pull the roots up anyway, so I just ground level off any kind of growth from those roots to prevent hoof problems. With a big patch of growth, it takes a while to get them all out. Honeysuckle is my worst woody growth plant and can't be ignored. It will double or triple in size over one season, so I cut it fast when anything shows it's leaves. Spraying probably won't work well, unless you can spray first thing in Spring when new leaves are out on Honeysuckle. Leaves get a waxy coating pretty quick, so spray won't stick or penetrate to kill the shrub if you are spraying later in the season.