I'll add that during good range conditions, 20% is overkill. Anything they eat over 16% is just pooped out.
VERY common misconception. This was propagated by a CONTROLLED study of PENNED deer who were fed NOTHING BUT CONTROLLED FEED. The number that was PUBLISHED and often quoted is that deer only can use/enable/process about 16% protein in their TOTAL feed.
The reality on a wild, LF ranch - the deer are going to be eating a LOT more than just the feed you put out. Who knows what protein/nutritional value it has. This is why they make deer feed in high protein percentage than 16%, otherwise it would be useless.
If your natural browse on your ranch is nutritionally poor, you can benefit from feed a higher percentage protein. VERY few natural browse on ranches in Texas have a 16% protein content. And those that do, don't need to feed protein anyway.
If you are breeding deer, and have breeding/holding pens, and are controlling their feed totally - then yes, don't buy/use more than 16%. However, if you are supplementally feeding wild deer in a free range environment where What, How much, and nutritional content is unknown - you very well can benefit from higher percentage.
For those who disagree with me - think about this. You have some feed that is 10% and some feed that is 16%. You mix 5 pounds of each - what the gross protein percentage of that 10 pounds of feed. If you said anything but 13%, then you need to check your math.
Now go out to your ranch. If your natural browse is 10% and you supplement feed 16% - and a deer eats the same about of each - what is the gross percentage of protein consumed? Again, only 13%.
Of course this is NOT quite accurate because a deer could eat natural one day and pellets the next, it won't be evenly mixed or processed by the deer's gut - but you get the idea.
The point is that buying/using feeds with 20%, 25%, or even 30% protein can - in some circumstance - very appropriate. That's why they make it.
For example, on one of my leases I use a timed Lamco trough feeder and drop a small amount of protein - I run mixed of feed from 26% to 30% because I know (through cam activity, etc.) that the deer are only eating a few handfuls of this feed per day, and the rest of what they are eating is nutritionally poor (usually).