Match the animal to the unwanted species. Different animals have different grazing preferences. For example, goats eat small oak, pine and willow saplings while cows generally do not. On the other hand cows would moo over a field of vetch while goats would be looking high and low for thistle, blackberries or dandelion.
Graze at the appropriate time of the year. If the primary goal of selected grazing is to reduce seed production of the target species, experience has shown that the longer the digestive trip, the less likely the seed will grow when dropped into a soup of rich nutrition in the field. Case in point, scientists speculate that the larger, more compartmented stomach of cows accounts for the lower percentage of weed germination, post cattle-grazing as fewer seeds emerge from the bovine's tail end intact and viable.
Feed only weed-free hay and silage for five days before moving livestock to a weed-free area to avoid spreading weeds.
Time grazing to allow native vegetation to recover between periods of grazing, taking care not to allow overgrazing as hungry animals may till up dormant weed seeds in the soil, exacerbating the pest plant problem, not controlling it.