Sorry I'm late to this party. I can maybe link studies later.
Salt levels, regardless of gender, should be
around half a percent. You will find that level
pretty consistently among
all feeds for
all purposes, from all
major brands. (as a sample) Note that if they display Sodium, not table salt, you expect a number around .3%
Re: Calcium.
Excess Calcium is ABSOLUTELY dangerous to your roosters. Also any pullet prior to point of lay, and any bird which produces small to medium eggs infrequently. There is no serious dispute about that fact, the biological processes are well understood, there is ample studies supporting it, and numerous anecdotes arising from mixing errors at the mills resulting in sudden mortality spikes.
But that's not the real question. As Paracelsus observed, "the DOSAGE is the Poison". To analogize it to human experience, its like smoking. No one can honestly telly you "
THAT cigarette will give you cancer." But they can tell you that the earlier you start smoking, the more you smoke per day, the longer you smoke, the more likely you are to develop one or more types of cancer and some related maladies. That's a matter of statistical certainty, used daily by insurers around the world in writing policies.
Excess calcium and chickens, the same way. Gout, urolithiasis, kidney damage, liver damage, intestinal damage of all sorts, reduced feed efficiency, inhibition of certain nutrient uptake, etc all become more pronounced and more frequent as the pathology progresses.
"Layer" feed is formulated mostly based on studies from the late 60s, 70s, early 80s as the cheapest way to feed production hens, under commercial management conditions, below which losses attributed to poor nutrition exceed savings from cheaper feed. That's where the 4% calcium +/- figure comes from.
If your birds aren't laying large to extra large eggs 5 days out of 6, those studies aren't intended for them. If you plan to keep your birds past first adult molt (when production tends to drop significantly), those studies aren't intended for them.
But what about all those very earnest posters who claim it does no damage, that they've done it for years?
Two responses.
One, they have no nul hypothesis against which to compare it - so they never see how much better their birds could be if they weren't fed excess calcium (and to be fair, some of the differences are so small as to be measurable in studies averaging hundreds of birds, but not observable by the typical owner. If your feed efficincy drops from .32 to .29, you will never notice it in a backyard flock, but over thousands of birds, you can bet a 10% increase in feed offered per pound gained is going to be noticed.
Two, many of the signs of calcium toxicity are clinically evident internally, but completely imperceptible externally. If you don't routinely take apart your birds, get a feel for things, those signs will be missed. And they may still, if your birds are young enough, be almost imperceptible. Is the liver more friable than normal? Could be a sign of excess calcium. Could also be a sign of excess fat (together with other symptoms), certain bacterial infections, and certain mold toxins. Hard to know for certain.... Is there a fine powder of grey-white sandy substance over the internal organs? That's a clear sign of excess calcium, but it may not be evident externally - unless you note it in a poor gait in the affected bird, or excess urates on the feces.
Finally, there are things in mitigation. Genetics plays a factor. There's a time component, mentioned above. The rest of the diet plays a factor. Diets high in nutrients whose absorbtion is inhibited by excess calcium don't result in deficiencies - the excess compensates for the inefficiencies the same way offering extra B1 inhibits the action of Amprolium, a common thiamin antagonist used to control coccidia. Phosphorus acts as a buffer. Feeds using dicalcium phosphate or calcium diphosphate as a significant portion of their calcium source cause less damage than those relying on oyster shell or another calcium carbonate source.
oh wait, you asked about excess protein, too. You aren't likely to pick up a bag of feed at the store with too much protein for chickens. Its too expensive, no one would buy it, and the benefits too few. Protein levels over 24% are associated with higher incidence of "angel wing" in developing ducks and other waterfowl. The only downside to 24% protein in a backyard chicken feed is cost. Broilers are routinely fed 24%, sometimes higher, protein feed to help support their extremely rapid development. A study intended to induce gout and urolithiasis in poultry thru excess protein fed almost 40% protein to get a significant sample of affected birds for measurement.
I usually recommend that the typical backyard owner, of the
typical backyard flock, with
typical backyard management practices feed an All Flock/Flock Raiser* type crumble to all their birds, all their lives, with free choice grit, oyster shell, and fresh clean water available at all times in seperate dishes. Without regard to age, gender, onset of of lay, condition of molt, etc.
*Essentially an 18-20% protein, 3.5% fat+/-, 1.5% calcium +/-, 3.5% fiber +/- feed, preferably with about .6% Phosphorus, at least .35% Methionine, and .7% Lysine.
Because its easy for you, and its good nutrition for them. Crumble because the chicks can easily eat it to, but if you have a mixed gender all adult flock, pellet is fine. If you ferment, pellet is fine.
and, in the interest of full disclosure, I don't feed my own birds the way I just recommended - in fact, I do almost everything I just suggested you not do. All my birds (ducks and chickens) of both genders get 24% protein for thier first 7-9 weeks of age, until they join the adult flock. I mix layer and a game bird feed (for reasons of cost) to obtain a 20% protein approx 2.8% calcium feed I use to feed all the adults, the rest of their lives. But most of my males are introduced to freezer camp between 8 weeks and 20. None make it 18 months before going to camp. My hens don't make it past their second adult molt, and many go to freezer camp sooner.
My reasons for that are complicated, its not something I recommend for everyone. But All Flock, all the time, for all the birds of all the genders is a safe and easy way to raise chickens, ducks, geese. Doing something different has limited benefits in limited conditions, and should only be considered after weighing all practical options.
Hope that helps.
My flock is in my Sig, below. You can see the results of me feed regimen
here.