Does anyone here have experience with using charcoal as an additive for poultry feed? thoughts on biochar bokashi as a feed additive? I have both straight up char and some biochar bokashi, wanted to try this with some friends' chickens, but was hoping to get some permie community insights before moving forward.
I found a permies forum post that mentions supplementing feed with charcoal: 
The most detailed guidance I was able to locate, excerpted from Ithaka Journal
Use of biochar in feed
In addition to its use as a litter additive, biochar, and in particular biochar bokashi, is also used as a feed supplement. Biochar promotes digestion, improves feed efficiency, and thus in particular energy absorption via the feed. Toxins such as dioxin, glyphosate, mycotoxins, pesticides and PAHs are efficiently bound by the biochar, thereby obviating any adverse effects on the digestive system and intestinal flora. The health, activity and balance of the animals will also be improved, as will meat and egg production. With animals’ immune systems stabilized, the risk of infection from pathogenic micro-organisms decreases.
The huge economic impact of diarrhoeal diseases in poultry is well-known. The causes of these diseases are often of an infectious nature and are caused by, among others, E. coli, clostridia, coccidia and mycobacteria. Of particular importance are salmonella and campylobacter germs; while rarely causing disease in poultry, they can do so in humans. Non-infectious causes of disease are in particular poor feed quality and biocide contamination of the feed, as when herbicides are used to siccate feed grain or to treat weeds during the growing of GMO corn or soy feed. The consequences are an increased susceptibility to disease, growth depression, infertility and digestive disorders.
Numerous factors are responsible for the stabilization of the intestinal milieu. Of particular importance here are the stabilization of the intestinal barrier and the functionality of the liver. Numerous bacteria such as lactobacilli and enterococci, but also non-pathogenic yeasts play an indispensable role here. Feeding biochar and biochar bokashi can stimulate the activity of these desired microorganisms in the digestive system. The benefit of the biochar lies therefore not least in its ability to relieve in particular the liver-intestinal circuit.
The charging of the biochar with specific lactobacilli to direct the symbiosis in the gastro-intestinal tract of farm animals can further potentiate the effect of the biochar. Biochar bokashis produced as ready-made feed on the basis of a fermented biochar, wheat bran and herbs are an important feed supplement for maintaining and enhancing performance in animal production.
According to studies by Van (2006), the addition of up to 0.6% biochar in the feed improves growth in young animals by an average of 17%. Similar results are confirmed by Kana (2010) and Ruttanvut (2009) for ducks and broilers. No systematic scientific studies of long-term effects exist as yet.
It is recommended to mix 0.4% – 0.6% biochar to the usual feed. With laying hens the feed supplement should be suspended for 2-3 days every 10-15 days. Biochar bokashis, such as Carbon-Feed from Swiss Biochar, should be added 2% – 3%% to the usual feed. If biochar is already used in the feed, the amount of biochar in the litter can be reduced accordingly.