With chickens: 

mill your chickens with 4 villagers like you would normally take berries and switch the villagers to berries when they finished (usually early feudal age)
Add some more vills to the berries aswell

If you are not supposed to take berries in dark age in your build order I would do a 20 pop up (19 vills) and mill the chickens anyway

With deers:

Take berries and lure the deers if it’s needed for your build order.