Ah. In that case, it sounds like they may be trying to modify them to fully fit in. So I wouldn’t be sure that, in Star Trek canon, Kzinti females are in fact biologically feral, and not just treated that way by a misogynist society. If M’ress is the same species, just a different culture, then we know Kzinti females are capable of sapience.
I am no Kzinti expert, but I think I read the same story as @Chronos which explains that Kzinti females are actively repressed by the patriarchy through genetic engineering and are not naturally unintelligent. And there are a number of normal, unmodified Kzinti females still around…
I stumbled across this thread and hoped it was about Interbred Chicken of Star Trek.
In Larry Niven’s Known Space universe Kzinti females are non-verbal and treated as chattel. On a trip to the Ringworld the band of intrepid adventurers encounter a group of Kzinti put there by either the Pak or their descendants. Subsequent to an adventure (because I don’t want to summarize an entire novel here) the Kzinti member of the party, Speaker-to-Animals, declares that he encountered a speaking Kzinti female. But speaking female Kzinti apparently no longer exit on Kzin or in the rest of Known Space.
The assumption is that at some point Kzinti genetics were tweaked to render the females non-verbal … but that doesn’t automatically mean non-intelligent, just not able to communicate. They are also not educated, so there might be a lot of under-utilized brain power there.
It also becomes apparent that the Puppeteer scheme to “breed” a less aggressive Kzinti paid off - the Ringworld kzinti are a LOT more aggressive and bloodthirsty than standard Kzinti, and that is certainly saying something. The Puppeteers engineered a bunch of wars between Humans and Kzinti, which the Humans kept winning, that seems to have killed off the most aggressive of the species.
The ST:Animated episode “The Slaver Weapon” was written by Larry Niven and is based on his short story “The Soft Weapon”. The two stories are pretty damn close, actually (the role played by Spock in the Star Trek version was played by Nessus the Mad Puppeteer in the original story, the Kzinti in both versions keep forgetting Human females are intelligent, etc.)
Me too. “Cat McCoy” is my take on him.
In “Treasure Planet” (a Known Space novel), there is a drug that allows modified Kzinti females to overcome the genetically imposed limitations.
Already near the beginning of “Man–Kzin Wars 1” there is a story where some guy discovers Kzinti females on a zoo planet, evidently from an old enough line that they remain un-genetically engineered. They even try to put some sexual moves on him, but he is too timid to go for it:
He is wise.
Also “Miss Kitty” (great Gunsmoke reference).
I believe this is the case with all the Star Trek humanoid species as well. They should all be sufficiently different on a genetic level to each other that interbreeding is impossible without significant genetic manipulation.
Given such significant gene-engineering, it should be possible to choose whether the resultant hybrid were sterile or not.
Ringworld Engineers:
The armored giant was gloriously happy. “All of this is most welcome news. Our worship is yours. We must seal the covenant by rishathra.”
“You’re kidding.”
“What? No, I spoke of this earlier, but Chmeee did not understand. Bargains must be sealed by rishathra, even between men and gods. Chmeee, this is no problem. You are even of proper size for my women.”
“I am stranger than you think,” Chmeee said.
From Louis’s ceiling viewpoint it looked like Chmeee was exposing himself to the giant. Certainly something had caused the giant’s startled expression.
Not exactly human is right and mating with a Kzin (KS) seems out of the question.
Well, if you insist on penetrative coitus involving the respective parties’ genitalia it might, but if you allow, shall we say, alternative means of pleasuring then the use of manipulative limbs/digits/whatever in a skillful manner might be a viable alternative for some purposes and ends.
One thing male cats have in real life are penile spines…
Anyway, what I gather from this discussion is that Star Trek writers tend to pretty freely throw around descriptions of characters as, e.g., half Klingon, half Romulan, half Kzin, and half Orion (whatever that adds up to 
without exactly worrying about how that works out in terms of number of chromosomes, or whatever. Why would they? Can such hybrids have children of their own? Sure, why not.
This discussion of humans and Kzin reminds me a bit from Harry Turtledove’s WorldWar series. If I recall correctly, an alien raised by humans from birth (well, from hatching) is attracted to human women because of his upbringing, but he’s not physically capable of anything satisfying with them, so he’s understandably unhappy with the humans who raised him (who had reasonably good intentions, by the way).
If the Federation/Romulans/whoever can genetically engineer the first generation crosses with species from entirely different planets they should be able to engineer subsequent crosses.
Assuming it’s done by genetic engineering as opposed to a technobabble solution.
Last night, I was watching a Season 2 episode of Star Trek: Enterprise, “Future Tense,” in which the Enterprise finds a small derelict ship floating in space, with a dead human pilot inside of it.
Dr. Phlox begins to examine the body, as the crew’s initial assumption is that they’ve found some experimental ship that had been launched from Earth years ago – and they wonder if the body is that of Zephram Cochrane, who had gone missing while on a flight; they’re hoping to identify the body, so that that they can notifiy his next-of-kin.
Phlox tells Archer and T’pol that the body’s DNA is very interesting – it’s mostly human, but he’s found a Vulcan gene sequence. Both Archer and T’pol are stunned by this; as far as was known at that point in the Trek timeline, a human/Vulcan hybrid wasn’t possible. Phlox then goes on to state that he’s also found Terrelian and Rigelian DNA, as well as others that he doesn’t recognize, and that all of the non-Human DNA appears to be the result of multiple generations of interbreeding.
They eventually figure out that the ship is capable of time travel, and that the dead pilot was from the 31st Century, suggesting that, at some point after the time frame of the other series (TOS, TNG, etc.), such interbreeding became more common (though how easy it would have become was obviously not addressed).