Adult geese with good forage don't need much feed, but they need some. Goslings on the other hand need a lot more while they are growing. They go from tiny fluffs to huge geese in 12 weeks. Ain't gonna happen on grass and a few grains, not with domesticated goose breeds. I have an adult goose who had plenty of green grass, and scratch grains, and she was a wreck. She'd been broody, and the broodiness took out all her reserves and she couldn't even walk for a while. A wild goose is habituated better to a more "natural" diet but domestics are bred for meat and fatness. All those genes screaming for calories and richer nutrition ain't gonna hang with a wild goose diet.
I know people do this, and do it successfully, but how many geese do they lose to mysterious illness? Probably a lot more than those who feed at least some concentrated feed.
I was speaking to the fact the OP's geese are goslings. A return to a more "natural" diet when they are adults, with once a day concentrates would probably be fine. But they need concentrates now, in more abundance than an adult.
I know people do this, and do it successfully, but how many geese do they lose to mysterious illness? Probably a lot more than those who feed at least some concentrated feed.
I was speaking to the fact the OP's geese are goslings. A return to a more "natural" diet when they are adults, with once a day concentrates would probably be fine. But they need concentrates now, in more abundance than an adult.