Sheep and Hay

So I've been scything and stockpiling hay through the late spring, as part of my plan to have plenty of feed when I finally find sheep. The challenge here is to bring them through the long dry summer when nothing will grow without irrigation. So now I have my sheep (two weaned American blackbelly lambs), and they are proving very resourceful at finding things to eat, and using up various things I scrounge outside their pasture. Acorns, all sorts of weeds, star-thistle, and prunings. They love roses and poplar. Now as the pasture is getting less and less at giving them anything, they've gotten interested in the bag silage that I also had made for them. But they show minimal interest in the hay! I was counting on them eating a good portion of it, and so not eat up all the silage. Is it because they are still growing lambs and need/want the better nutrition likely present in the silage, which was cut from younger grass? I suspect they would eat the hay if I starved them into it.....i.e. not give them anything else, but I wonder if I would stunt their growth or otherwise harm them thus?

Their propensity to eat hay depends on the quality of the hay, but they will usually only eat hay when there is no green forage available. They will also eat hay in the spring when the new forage is very lush and they need some dry stuff to balance it with in their rumen. When they are eating hay, it also helps to occasionally provide a protein block to provide any nutrients that may not be in the hay. My sheep gain weight on hay.