Thanks for replies, makes sense not to keep feeding them for too long I guess. Hy-line are apparently a white leghorn type but hy-line is a big American company with producers here too, their website is quite impressive. I don't know too much about chicken genetics but they are super layers so I hope they girls will be good! They are a brown hen (cockerels are white so you can tell the difference at hatching). I have one who has actually changed; he started off white but has now grown brown feathers? Not sure which pen I'll be putting him/her in! Is it possible the genetic colour sexing sometimes fails?
Mixed corn I suppose is not too expensive, or perhaps some plain wheat direct from farm would be a cheaper way of feeding them? Are there any other straight grains that they can have oats or barley?
Thanks again for any tips.