I think giving any farm animal from chicks to rabbits to cows a large diversity to choose from is really important from the start. They have amazing instincts, and will go for more greens if that's currently necessary, then later may seek out more seeds or grains, or even certain herbs they usually avoid but may be temporarily medicinal.
As a kid I lived in town with a large backyard. I raised ducklings without special feed, and instead on boiled eggs, cottage cheese, dandelion greens, and we would go on hunts together with me lifting large rocks and they grabbing at bugs and getting sand for grit. (I'm not recommending that diet today but they did grow up very healthy, most likely the bugs and grit were important components to help the other stuff digest). As adults they adored dandelion greens above any other greens in our lawn and attacked and ate them like piranha. At the time it was great because my parents didn't want dandelions in the lawn and they really kept them in check.
In later years on a farm raising ducklings, I gave them handfuls of mixed pasture greens to peck at but didn't keep it to only dandelion greens. As adults they liked all greens equally... grasses, clover, a bit of dandelion. I've heard others say they have taught young farm animals to eat specific weeds by getting them to favor them while they're young.
But getting them to eat specific weeds isn't as important as their health and an otherwise diversified diet while young and not able to free range.
