Female sheep want little to do with male sheep most of the year. The male sheep actually prefer homosexual sex to heterosexual sex. Why is this?
Brains have a "dis-inhibition" switch, where the brain is organized to inhibit the desire to mate with the same sex but this switch varies significantly. This switch tells the animal that sex with the same sex is less desirable, but works in a pinch. This is why we see many animals exhibiting homosexual behavior but immediately switch over when the opposite sex is around and willing. Switches can be manipulated by chemicals and sometimes individuals can be naturally "disinhibited", making their capacity for same sex attraction fixed in the "on" position.
In autumn, female sheep come into heat and only during that time do the males seem interested in them. This is not because the males become interested in female-ness but instead the females begin to act and smell different causing the males to now be interested in them. They allow the males to use male-like foreplay (kicking, sniffing, grunting) just this once, and once the females become pregnant, they once again smell normal and are not interested in male-like foreplay, causing the males to ignore them once again and return to homosexual sex.
Though males react to the female's change in smell and behavior, some males don't react to this at all and actually prefer the same sex all year round. Gay males act like males, using male foreplay, but only with other males and the hormonal surges they receive around other males is the exact same as the males around autumn females.
They are naturally attracted to the opposite sex because their brains are organized that way.