“Enhancement of sperm quality and fertility-related parameters in Hubbard grandparent rooster fed diets supplemented with soybean lecithin and vitamin E”:

https://pmc.ncbi.nlm.nih.gov/articles/PMC8749332/

Conclusion:

They found out 1% of diet from soy lecithin was the sweet spot for semen volume in roosters. Also, vitamin E is synergistic for sperm parameters.

Study #2

“Semen quality, testosterone, seminal plasma biochemical and antioxidant profiles of rabbit bucks fed diets supplemented with different concentrations of soybean lecithin”:

https://pubmed.ncbi.nlm.nih.gov/22558930/

Conclusion:

Found out also 1% (of diet by weight) was best for rabbits

VERY IMPORTANT: human equivalent doses using animal conversion factors (estimates):

For a 70KG mf:

1% of diet from lecithin (for reference) 15g to 20g

Rooster study equivalent : 5.6g a day

Rabbit study equivalent: 11.3g a day

Limitations:

Studies were done with soy lecithin, I suggest assuming a 1:1 ratio or assuming sunflower lecithin is slightly more effective.

Practical takeaways: I will try about 7g a day, higher than some typical recommendations of 2 or 3 grams.