[BLTN]

That’s one of the difficulties with horse manure, it retains many of the weed seeds intact. Cattle, with their four stomachs, destroy more weed seeds in their digestive process so you get fewer (but still some) in the garden. Getting the compost hot as it breaks down is the only thing I know…or using heat on the weeds themselves when they first come up (flame weeding) before planting your garden.