But the moral case may still stand: is the pornography necessary? Farmers, animal breeders and vets all have extensive experience of getting viable sperm out of male animals under artificial circumstances, and they have approached this very question, albeit tangentially.
Hemsworth and Galloway showed in 1979 that sperm count in the ejaculate of a domestic boar (I mean an actual boar, that’s not a euphemism for men) was significantly increased by allowing a “false mount”, or observation of another boar’s semen collection. I wouldn’t want to overstate the evidence: another study found that the effect seems not to be present in rams. But in 1984 Mader and collagues studied 12 Hereford Bulls and found that watching another mating pair in action significantly increased frequency of ejaculation. That very same year, Price and colleagues found semen collection from male dairy goats was faster with a “stimulus female”, which was present, but unmountable.