One thing we were told was great for rescue hens was to give them plain yoghurt. I think you were only supposed to do it until they had acclimatised - but ours still enjoy it every morning. I make it for them as it means we don't have to keep going and buying cartons of it.
It is so easy to make - you just need one of those wide necked flasks, mine holds 900ml. Heat the amount of milk that will fit your flask until just before it reaches boiling point. Once I see those tiny bubbles forming, but before they break, I take it off the heat. Leave it to cool until you can put your finger in it - still hot, but bearable. Stir in 2 tablespoons dried milk powder. Put a small carton bought plain yoghurt into a jug, mix in a little of the hot milk and mix well. Add the mixture to the rest of the milk and stir to combine. Pour into the vacuum flask, seal it up and leave overnight. In the morning you will have lovely thick, plain yoghurt, which, if you are not a chicken, you can flavour or not, as you choose. Soft fruit, rhubarb - whatever takes your fancy. Empty into a jug or bowl, cover, and keep in the fridge.
When you want to make some more, just save a small amount ( about the size of the small carton) to start off the next batch. The measurement is not critical.