My background is biochemistry/microbiology. I do grok this stuff. I read a lot of material from JCEM and other professional sources. If this isn't relevant, explain why oral hormones work across species. How much is absorbed varies somewhat, but that's a dosage detail (frex, the oral thyroid dose for a dog is 10x that for a human by weight because dogs don't absorb it as efficiently; however once absorbed by either human or dog it still does the same job, and it doesn't matter if it started life in a pig or a rat, and barring deiodinase deficiency, doesn't even matter if it was synthesized in a laboratory, as is most prescribed today).
Do you know where oral progesterone for human use comes from?? Hint: not from human sources.
JCEM: Journal of Clinical Endocrinology and Metabolism