I've been reading the Feeding Poultry book.
It defines a bird "in production" as a bird which is growing, regrowing feathers after molt, recovering from an illness, laying, etc. Specific to laying, it says this about protein requirements:
Feeding Poultry
Chapter 13 [starts on page 383]
Feeding and Management for Egg Production
[I've retyped this, so please verify everything for yourself. Full text, including footnotes, is available to read for free online at this link:
http://babel.hathitrust.org/cgi/pt?id=coo.31924003011545;view=1up;seq=399 ]
Protein. Satisfactory production cannot be obtained unless additional protein, besides that found in grains, is supplied.
Halnan made the accompanying estimates of the protein and energy requirements of a laying hen.
Hens in production require a continuous supply of protein since the nitrogen required for egg production is largely, if not entirely, drawn from the food. An insufficient amount of protein will result in decreased egg production, lower body weight, and smaller egg size. A shortage of albumin in the ration has been reported as resulting in pickouts which ceased directly after albumin had been fed.
Where birds were given the opportunity of balancing their own ration, some birds laid well and gained on a 12 to 13 per cent protein level while others wanted or required a higher level. Non-laying birds thrived and prepared to lay on an 11 per cent protein ration. In general, egg production was in accordance with the protein level, but the highest levels were not always the most economical.
Experimental results generally show that a ration containing 12 per cent protein was not sufficient for satisfactory egg production, body weight, or egg size; that the 14 per cent protein ration gave satisfactory egg production but did not maintain body weight at all times and was not conducive to best egg size; that the 16 per cent protein ration was satisfactory in all respects.
Workers in the United States Department of Agriculture report that increasing the percentage of protein in the diet, within the limits of 11.2 percent and 23.6 per cent by the use of protein supplements of different origin, augmented egg production (1) by increasing intensity of production, (2) by increasing egg weight through direct effect on yolk weight, and (3) indirectly by increasing body weight and yolk weight, thereby increasing albumen weight. INcreasing the protein level, within the limits stated increased the quantity of egg produced per unit weight of feed eaten. Increasing the protein content decreased the efficiency of protein for egg production.
In studying the relationship of ruptured yolk to fowl paralysis, Moore reports that results over a period of 3 years indicate higher mortality from a flock receiving a 13.5 per cent protein ration than from on receiving an 18.5 per cent protein diet. Bronkhorst reports higher mortality do to prolapse from pullets on a basal mash containing 10 per cent of meat meal than from pullets fed mixtures containing 15 and 20 per cent of meat meal. Prolapse was frequently followed by cannibalism and did not appear to be influenced by egg size, egg yield, or age at sexual maturity.
Byerly suggests, as a result of food requirement studies, that possibly smaller birds require a higher percentage of crude protein in the diet than larger birds, for the same degree of production.
The question might arise concerning a possibility of feeding an excess of protein. The Western Washington Station states that all-mash rations containing 30 per cent of a protein concentrate did not produce a high percentage of organic trouble. It would appear from this, as well as from the experiences of others, that hens can tolerate a fairly high protein ration if other conditions are favorable.
As a general summary, it would seem that in order to promote satisfactory production, maintain body weight, and secure good egg size, the ration should contain 15 to 16 percent of protein. Part of this should come from animal source. If the birds are on good range, favorable results can be obtained with a lower amount of protein in the ration.
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There is an awful lot said in that last sentence, no?