Well, I will agree that it doesn't keep the ab walls from stretching, but rather stretches them to their limits so there is no room for anything else... Um know, I didn't go off topic, everything I posted was related to diet, even if you had to read down the page a bit. Yes some may be opinion... but some of it is real!
http://www.wattagnet.com/articles/14516-how-nutrition-affects-hatch-ability-in-broiler-breeders
Yes there is a certain amount of fat required to be able to produce eggs. Your body and brain must have fat in order to live. Some vitamins are fat soluble. But too much fat is bad across the board for fertility even in males. Most of the studies I could find were more related to supplements effecting weight and there by affecting fertility, mobility, and hatch-ability. And as much as we would like to think chickens will only eat to meet their energy needs, I'm gonna say hog wash! That would be true if their wasn't candy bars of corn laying around in front of them. But even with nutritious feed next to it... chickens love corn and scratch and will eat until it is gone. Maybe not true for people who are feeding more whole feed than processed feed. They eat to fill their crops... even if it's with styrofoam or cardboard. So if you are providing scratch corn on the side you are dumbing down the nutrients of your main feed while maintaining a high caloric content. A high calorie, no nutrient feed will not produce viable chicks, if even eggs for very long. Which by the way... is the point of this thread, producing healthy chicks.
Yes, birds in cages lay... that is a crazy argument. And decreased production because of activity is true for serious athletes who have too little body fat... maybe true for chickens, IDK... but I can guarantee you which is going to live the happier longer life. The rest of the body in the cage is suffering!
So what if someone made the mistake of saying never feed corn during lay season, it clearly wasn't meant for the commercial product. But a grammar Nazi or someone worried about proving something might pick out a certain word to stick on.... that's their choice. But it's better to take things in context and if it needs clearing up, why not do so in a friendly manner?
If you've seen commercial feeds that aren't balanced, please report them, so the rest of us aren't feeding our birds an inferior product that isn't what it claims to be. Whoever the organization is that regulates it would have a huge interest to know as well! Think AAFCO for dogs but not sure if it's the same for chicken feed, it's probably printed on the bags.
I agree, other nutrients are just as important as calcium.... It's unfortunate that we can rarely ever get an accurate picture from any one article. :/ And so many will grab a small detail and run with it while missing the big picture....
I agree that the key is BALANCE!

(and since I use commercial feed will likely always include some corn... but no extra corn scratch on my watch.) Also even doing "nutritious" treats can throw the balance off.
I can't even begin to tell you how many problems I see from people "spoiling" their chickens with treats. Goes all the way from not laying to death....
Again... we are in agreement, BALANCE is key.
Best wishes and happy breeding/hatching!