Welcome back to the Lane and to chicken keeping
I'm in NZ so have no idea what's available now in the UK but if you look at any good poultry tonic I don't think you'd go far wrong... and maybe something with corn in it which is high in energy and will give them the energy they need to produce heat during the night.
Oh and Apple Cider Vinegar (ACV) in their water (20mls per litre) - there have been studies done that show that hens that have ACV grow feathers back quicker than those that don't.
It's a great way to aid their digestion (helps them process proteins more efficiently), helps lower the pH level in the digestive tract so makes it less welcoming to pathogens like E.coli organisms as well as Coccidiosis.
It's a great source of Potassium (which helps them use calcium efficiently) so can be great if you have any hens laying soft shells as it helps them free up the calcium they need for laying down the shell.
If that wasn't enough it also helps prevent the growth of algae in your drinkers so for something that doesn't require much effort and isn't hugely expensive it has great outcomes ...and just so you know I don't work for an ACV company
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