ditto what twistedwire said,
chickens will eat less when they are hot.
On the other hand, I also had some resistance to Layena, and back then the temperatures were moderate, but I may have switched them faster than I should have. They say to mix old and new feed for 7-days when you switch feed types.
I would like to get the impression that my chooks are really enjoying their food. They seem to be really hungry early morning and late evening---and it makes me wonder how 'good' what I am feeding them is. I will be interested to see what other answers you get to your question!