Originally Posted by Natja
According to Sex at Dawn, one of the best ways to increase sperm production/sexual desire in males is more akin to what we would colloquially call Hotwife or cuckoldry.
I saw a show about that on Discovery once, on that series they had about Sex.
This one has a much simpler explanation: a man who produce more sperm when seeing his mate with other men has a better chance of competing with their sperm, thus increasing his own chances of reproducing.
The same effect happens when a man's mate goes on vacation. His body assumes she spent the time away mating with other men, and so his body jacks up the sperm production in order to compete.