Table 1. Shows the percent protein required for quail. Looking at it you can see why I choose 24% protein.
Table 1. Recommended levels of crude protein (%) for domestic quail.
Starter/grower Finisher Adult/breeder Author
24 20 - Wilson et al. 1959
20 - 18 Murakami et al. 1993
21.6 - - Hyankova et al. 1997
- - 22.4 Pinto et al. 1998
- 24 20 NRC, 1994
24 - 18 Musa, et al. 2008
24 20 - Lee et al. 1977a and b
and here's the thing. 24% isn't wrong - but its not right, either. In the US, higher protein feed is relatively cheap - we have a lot of farmland producing grains, so we tend to feed higher protein feed because, typically, higher protein = higher key amino acids.
Modern feed science has started looking very carefully at the amino acid requirements to figure out what the "perfect" protein is, and it turns out you can have a lower total protein %, as long as the levels of certain key aminos is higher - that's what the EU does, lower total protein % with higher %s of certain aminos that make up that protein.
As I think
@007Sean said (maybe another poster), the Lyine and Met levels in that feed (the two most important limiting AAs) are relatively low in those feeds. I'll look later, see if I can't find some more modern numbers for quail.
For (Chicken reference) I don't feed anything under .4% met, and I look for at least 1.1% lys - the two are resonsible for connective tissue development and muscle growth primarily, and are absolutely critical to developing birds. As they age, and growth slows, becoming maintenance, their needs drop. My current feed that I raise my dual purpose chickens on for the first 8 weeks +/- is 1.4% Lys, 0.5% Met (used to be 1.6 / 0.6% - they reduced it to save costs.)