This is an important point. It is the extreme laying performance of the modern production hen which demands extreme feeding to make all those eggs.
Somewhere along the line the 'minimal' that feed manufacturers aim for has turned into 'optimal'. How did that happen?
What about the definition of minimal?
Perris, since you seem to be asking in good faith, I'll take a stab at this.
Commercial "Layer" formulations are largely based on studies from the 60s, 70s, some early 80s. They were intended to determine the most cost effective way to feed commercial egg layers under commercial mangament conditions, where further reductions in the nutritional quality of the feed would result in additional chicken and egg production losses (on average) costing more than would be saved in reduced feed expense. That's where the 16% protein, 4% calcium figures largely originate.
It is both a purpose-built feed, not intended or well suited for anything but commercial layers under commercial mangement (i.e not hatchlings, not roosters, not "show silkies" - just prime age leghorns and similar breeds/hybrids such as the various RSL and BSL production lines intended to be kept only till first adult molt, then sold for some other purpose, such as pet food.) I think it a good example of "minimal".
Obviously, costs have changed since then, science has improved (Met levels can now be measured independently, when at the start of those studies, they were impractical to measure at all, and for many of those studies, Met + Cys or SAA sulphur containing amino acids were measured.) Europe, which is at the cutting edge of synthetic amino acid research in the poultry world has studied the matter further, finding that for commercial layers, commercial conditions, crude protein can be dropped to 14% without significant impact on production IF synthetic methionine and lysine are added to bring feed values up to certain target numbers. Here in the US, owing in part to cost differences associated with our various crops, higher crude protein levels (i.e. the old 16% figure) are more frequently seen, based on the old research, and likely in part based on consumer habit.
Now, if you were to pull up a Cobb 500 or Lohman feed manual, you would find a number of target numbers for various amino acids, crude protein, fiber, fat, vitamins, etc usually in three week blocks or so setting forth targets intended to maximize broiler growth of those lines at those ages while minimizing losses due to diet and genetic propensity. That's more like "optimal". Obviously, a Cx will (on average) survive on lesser nutritional values, it grows more slowly, never reaches the same feed efficiencies, isn't as robust from a disease or parasite challenge perspective.
Of course, Cx are intended for table, and those optimal growth recommends are intended to support that end use. SO perhaps they are a "bad" example of optimal.
There are also "optimal" targets for birds which can be determined from review of the research with a concern other than minimal cost. We know, for instance, that higher than 16% protein feed (setting aside, for the moment, iindividual amino acid targets) is better for the birds than 16% protein feed, being associated with increased feed efficiency, more robust immune systems, faster growth rate, larger overall size, increased productivity in frequency of lay and average size of lay. We ALSO know that those improvements are relatively minor (often on the order of 1-3% ea), and not strictly cost effective - and yet many backyard chicken owners choose such feeds and/or recommend them because cost isn't a first concern and we (well, some of us) are interested in a longer average life for our birds than a commercial egg laying facility. That's closer to optimal. The same can be said if we look at CA : P ratios (and even P-type), individual amino acid levels, niacin levels, and a host of others.
and at some point, additions in nutritional value cross into a range where they have either no measurable benefit over any reasonable time scale or even begin to pose a danger to the birds they are intended to feed. Fat levels go from recommends around 3.5% (a little higher for waterfowl) to about 6-7% (for "finishing" Cx before table) to percentages associated with much higher incidence of fatty liver disease.
Calcium needs for most birds are around 1-1.5%, birds actively laying need more (how much more being dependent on frequency and size of egg shell of course). That's not well studied axcept in commercial layers under commercial conditions - so offering a free choice calcium source (i.e. oyster shell) allows a laying hen to eat to meet her needs in addition to the 1%+/- minimal supprot she recieves in her All Flock/Flock Raiser mix. Another common recommend by posters here at BYC.
We also know from experiences when calcium was mis-measured at the mill that very high levels of calcium are dangerous even to prime layers, with reports of rapid increase in mortality of birds accidentally fed with 10%, 15% calcium mixes, just as we can see the clinical results of excess calcium build up in old roosters, and limited studies on the effects of high calcium levels in birds of both genders prior to onset of lay.
That 'more than minimum, less than dangerous', nothing in the feed that's likely unusued/wasteful to any particular degree feed for our birds, management, and purpose is "optimal". and of course it varies - a Cx and a show Silkie and a Production Red have very different purposes, and somewhat different dietary needs.
