Keep in mind long-term concerns aren't a real factor in the research regarding cattle, as they tend to be slaughered in a short period, relative to the life expectancy concerns of us humanids anyway.
And plenty of research has been done on humans and the negative effects of soy. The problem is that the Soy industry has deep pockets, and like the tobacco industry, has a well funded crowd of attorneys, and in-the-pocket researchers who launch well-funded all-out assaults on any negative findings by other researchers. And the sad reality is that they do and have done just that. Some poor scientist somewhere finds something alarming, and then a roomful of Big-Soys paid researchers start tearing like bulldogs at every nook and cranny of his work, A roomful of attorneys jump in . . . and . . . well . . lets just say that most ethical nutrition researchers aren't real eager to even try to take them on. The few who have, have paid dearly for their transgression against Big Soy. And soy interests are HUGE Business globally, and they fight dirty.
You can actually find some of the dirt, or at least shadows of it right in the "Pro Soy" information, if you look carefully. Believe me, not only do they have attorneys and crooked researchers on staff, they have spin doctors, sometimes literally, too. Unflattering information is often not so much in the "fine print" as much as it is usualy broken up, divided and sprinkled throughout an entire report, usually with very benign-sounding, matter-of-fact, carefully crafted wording.
Of course soy isn't going to kill us in a week. Or a year, or maybe even a decade or 1/4 century. And the Soy industry relies on that fact. It gives them plausable deniability. Even though I believe it is crap, even I myself won't necessarily not eat something with soy in it. I just try to keep my personal consumption to a bare minimum. Same with my horses. It's hard to NOT feed a horse some soy nowadays, it's in all sorts of animal feed. But I sure don't use soy to give supplemental fat or protien. Horses are more at risk in my opinion than cattle, because horses live long enough to be concerned about fairly long term risks of making "a bad call" nutritionally, whereas cattle, where most of the feed research comes from, usually end up on our plates within a few years of birth.
All this said, if someone wants to use soy, hey, that is their choice. Have at it. But for me, there are simply too many less risky alternative out there, that don't have a HUGE cadre of attorneys and other professional and regulatory lackeys so willing to sweep soy dirt under a soy-fibre rug.