But it’s very important to give complete feed too from late fall till early spring when there’s not much food to be found in the garden/ fields/ woods.
In fact the mixed grains should always be supplemental.
There are many ways to make a complete feed and even more ways to ensure a chicken gets to eat a complete feed.
To be clear, what makes a feed complete, in the eyes of the commercial manufacturers is a particular set of amino acids. The ratio of these amino acids varies from feed to feed. The feed for a large commercial concern is often designed for them by the manufacturers.
The one amino acid that the commercial manufacturers have problems with is Methionine; the chicken can't make its own and it is difficult/too expensive or prohibited by law to source from a natural product.
I believe the vast majority of commercially produced feeds have synthetic Methionine added.
This wasn't a problem when animal products, usually fish-meal, could be a feed constituent,
So, the idea that mixed grains, without defining which grains and how much of each are only fir for a supplementary feed is misleading to say the least. After all, most of the commercial feeds are mixed grains that have been processed. Naturally, the feed manufacturers choose the cheapest grain that will get the job done.
For example one can by wheat with 17% to 18% protein content, but it is really expensive. One could do as I have done and give chopped Brazil nuts to boost Methionine when one believes the amino acid content of the whole grains given might not provide enough. Thing is Brazil nuts are fiendishly expensive to use as a feed additive.
I just want to caution against the idea that a) only commercial feed can supply the correct balance of amino acids, b) the 10% rule is so misleading, but as you wrote, it may be the best option for fully contained high production hens in lay.
