those are the numbers that are usually tossed around, or close enough. No, they aren't accurate. Yes, for most purposes, they are close enough that your birds won't die from them.
We all know where the 4% calcium number comes from - its the studies of commercial layers in commercial conditions, at prime laying age. If your birds aren't commercial layers at prime laying age, they need less calcium (say a 4 or 5 year old Brahma, insted of a 10 mo old Isa Brown).
The Phosporus number looks low and is likely
digestible P, not total P. Chickens basically can't use phytate (plant-based) P, so to the extent your feed shows total P including the phytate P, your number will need to be higher. There are some enzymes being used in many modern feeds which help overcome that somewhat. I personally look k for P of 0.5% or 0.6% in all my feeds - P, by the way, helps buffer some of the effects of Calcium toxicity (so do other forms of calcium which generally aren't used in the feeds I buy), so a little "extra" has some benefits. Also, my birds aren't production layers and my hens free choice oyster shell to get the rest of their calcium, which lowers the effective ratio), so...
I'm weaker on Vitamin D needs, haven't read enough studies to form a strong opionion w/o looking back at the studies, but my sense is that it is also low.
Here's a resource from India which republishes some older American numbers I can't easily find direct links to. I've not checked every vitamin or mineral, but the few I have looked into rely on studies from the 70s-90s which seem reasonable. Its Ca / P ratio is the old 1.0 / 0.4, higher than PoultryDVM (which isn't written consistently by Avian vets, btw), and lower than the more modern studies (and my preferences).
The key to this article whose chart was linked to in the above is the resources/studies relied on, listed at the bottom of the page. Those are neither the best, nor entirely the more recent, studies. However,
one of them (on Ross BROILERS) is quite good and relatively new. Recommend you start there, and use it as the seed for your research, because it starts with a lot (compared to many studies) of young birds, when Ca to P ratio has its greatest performance effects.
tl;dr? The best performance was between 5-6 g/kg non-Phytate phosphorus, with calcium intake between 8-11 g/kg, AND (shown in many other studies) that chickens would eat to their calcium needs if required, but were much less effective at eating to their P needs. lending further support to those who choose to free choice calcium as part of their feed management program. This result should surprise... NO ONE.
You should also consider the studies themselves. Most studies are focused on commercial birds, under commercial conditions, with commercial lifespans. That does NOT make them inherently bad. That many of the older ones were paid for by feed companies or chicken producers does NOT make them suspect. What it does do, however, is embed certain assumptions that likely aren't relevant to your flock. Published numbers like the ones above come out of those studies, with thosse assumptions. Mostly, the studies look to see how LOW a particular nutrient can go before it has commercial impact over a commercial timescale. That's fine if you are raising broilers for freezer camp at 8 weeks at lowest possible cost. Its not fine, if Henny your daughter's favorite EE is expcted to be the family pet for the next 7+ years.
Virtually all biological processes concerned with Ca / P use the two at a ratio of 2:1, particularly bone building and maintenance.
Not for chickens, for essentially all animals (even us humans) - Nature doesn't routinely reinvent the wheel. The exception is shell building, as egg shells are almost entirely calcium carbonate (CaCO3), almost no P whatsoever - which is why production layers need amounts of Calcium damaging to all others. That leads to the next obvious observation - a chicken laying six large eggs a week (prime Production red) needs more calcium to support that than a chicken laying two-3 medium eggs per week (my 3yr old SLWs). Another point in favor of free choice oyster shell for mixed flocks, "vanity" flocks of differing breeds, and barnyard mixes of variable performance.
Hope that helps, enjoy your readings.
