I know that, but they lose muscle mass during the winter due to the cold because of insufficient protein from their regular feed.There will always be a mill date on the bag. Sometimes it is hard to find, sometimes it is obvious. Many companies like Nutrena will print it right on the bottom of the guaranteed feed analysis tag with the day, month, and year clearly understood.
Purina, Dumor and others print it on the seal at either the top or bottom of the bag. It isn't always obvious but it is there.
Some, like ADM use the Julian date which is harder to decipher. That is the day of the year. 001 will be January 1. March 1 will be 60 or 61 depending on if it is a leap year. December 31 is either 365 or 366 for the same reason.
Still others like Fertrell will have a date code with 2 digit, month, 2 digit day and 2 digit year followed by which mill run of the day it was.
If you still can't find it, ask at the feed store. There's a 50:50 chance someone there will know. Otherwise, call the manufacturer and they can guide you.
As was said, if still no luck, buy something else or elsewhere.
I occasionally use that for certain purposes. I know it says 'grower' but a 15% feed is a finisher feed. Dumor used to label it 'finisher' about 8 years or so ago.
Finisher is usually for finishing meat birds but I use it for roosters and maturing cockerels since they don't need as much protein.
It all depends on the productivity of the birds in question.
Birds building 5-7 egg shells a week will likely need more calcium than that in layer. Hence, oyster shell, crushed egg shells or limestone.
Medium production birds will find layer to be sufficient.
For poor producers (0 or 1 egg a week), layer may be too high in calcium
1% calcium is sufficient for all non-layers (chicks, roosters and any mature hens out of production).
Most layer feeds are in the neighborhood of 3.5-4.5% calcium.
Large scale poultry producers have their own mills and are able to customize formulas to meet the needs of their specific birds. For example, for growing pullets, they will begin to feed a pre-lay diet about 2-2.5% calcium at about 16 weeks.
The rest of us are stuck with the selection at the feed store.
Needless to say, one size doesn't fit all. As you noted, in backyard flocks, the needs vary dramatically.
Furthermore, it isn't always about the calcium percentage. Other nutrients like phosphorus and D3 play a great role in calcium utilization. For example, if no D3 is present, they can't uptake calcium at all. There are many other variables as well including acidity level of feed and water.
Energy comes from carbs, starches, sugars and fats.