I've been around sheep and cattle alot, all my life. That's got to be one of the most ridiculous research projects I've heard of - I see very little correlation between homosexual behavior in livestock and in humans. Maybe in those people deprived of access to the opposite sex, but that's certainly not the reason for most homosexual behavior in humans.
Homosexual behavior in livestock can be observed in man made enviroments - a group of pubescent or older rams or bulls penned together and away from females of their species will exhibit homosexual behavior. Take the same group of males and turn them out with a group of females and they will no longer be interested in each other, only in the females. Sure, some will display a higher sex drive, but whether with other males or with females, the same individuals will be more aggresive than others. By the same token, in a group of females with no males present, the females that behave sexually toward each other are usually all in estrus. Or a female in a certain stage of pregnancy or some other heightened hormonal state (such as might be caused by an ovarian cyst or other reproductive proplem) will behave sexually toward a cow in estrus. But put a bull in the group, and the other cows quit paying attention to the one in estrus.
Livestock in a natural envroment have sex for one reason - a natural drive to reproduce. They have sex only when the female is in estrus, which is the only time she can get pregnant. A bull (or a ram) or even several of them with a group of cows (or ewes) won't show any sexual behavior except for when a female is in estrus - even over the several month time frame when all the females are bred and not cycling. I've yet to ever see or hear tell of a bull or ram that was physically able that would not attempt to breed a female in estrus, or a female in estrus that would refuse the attentions of a male.
Peoples sex drives tend to be a bit more complicated... The desire for sex, whether heterosexual or homosexual, is far more emotionally driven than an animal's simple drive for reproduction. Cutting into a sheeps brain to try to explain that is pretty absurd.