It is true that raw spinach contains a fair bit of oxalic acid which interferes with the absorption of calcium. That can affect egg quality and the health of the chickens. A lot of poultry websites caution about feeding too much, some say it is not worth the risk as you can’t accurately predict how much oxalic acid the chickens are intaking.
Mine sometimes get raw spinach and I am fine with them having it as an occasional treat. I wouldn’t be chucking it in daily though.
