A pasture was a field where livestock was allowed to graze.
One could be said to be "put out to pasture" (Star Trek V: The Final Frontier) or head for "greener pastures". (DS9: "Tears of the Prophets")
In 2269, Spock compared the matter-energy cloud's feeding on planets to be analogous to "a huge bull grazing here and there in the pasture of the universe." (TAS: "One of Our Planets Is Missing")