This is WILDLY incorrect, sheep are my special interest and I've been raising them for over a decade so excuse me while I get up on this soapbox: ewes do not have a standing heat. Cows reportedly do, but not sheep.
a) ewes who are in heat and feeling flirty solicit sex by walking other to someone they're attracted to, then turning their backs, peeing, wagging their tails, and making extremely flirty bedroom eyes over their shoulders at their crush. Also try to murder anyone they feel might be a rival for suitors. Also also try to murder her crush if it turns out they're not keen on her. Ewes in heat but not feeling flirty (yes this happens) walk around all business as usual and you only know they're in heat bc of the crowd of hopeful suitors following her around and fighting each other. Either way it's not subtle.
b) ewes DO mount each other, with great frequency and enthusiasm. If this is mentioned at all, it gets written into the literature not as a sexual act but as something ewes do to visually signal to rams that they are in heat. (If a ram is within a mile and not dead I promise he doesn't need any such signal) A 'lesbian' ewe will follow a ewe in heat and try to run all the other suitors off to keep breeding rights to herself just like a ram would, whether she herself is in heat or not.
c) it's really really easy to tell what a ewe is attracted to by who she mounts/lets mount her and who she head-butts away from her with murderous intent. Most ewes are more or less indifferent to gender. Out of two dozen I currently have one(1) exclusively straight ewe, and two(2) exclusively lesbian ewes, everyone else is in between.
As far as I can tell the real reason there's no "concrete facts" (sarcasm) about lesbianism in sheep is first off, in a commercial flock ewes that don't get pregnant every year, preferably on the first heat of fall, get culled. No one bothers to determine if she's infertile or just doesn't like rams, so lesbian ewes determined enough to actually stop rams from breeding them don't last long, and secondly that most people researching homosexuality in livestock I've experienced are either stuck in a Victorian "two feemales can't have sex cause there's no peenus for penetration hur dur" mindset or in an equally outdated male-actively-chooses/female-passively-chosen mindset and it just doesn't occur to them that ewes might have preferences.
