I've heard this claim, and I'm inclined to think that it's true, given the low PUFA content of ruminant fats. I'd still like to see a source though, and the mechanism by which this happens.
Additionally, it's kind of weird how especially cows, but also sheep and goats, tend to have somewhat "rectangular" hindquarters--not very accentuated at all.
Horses and especially pigs, however, do. Do you think this is a consequence of PUFA neutralization (horses and pigs aren't ruminants, and thus wouldn't neutralize PUFA), since PUFAs tend to be preferentially stored in the butt/thighs?