Horses do engage in same-sex sexual behavior, including mounting, courtship displays, and genital investigation. But whether that qualifies as “gay” depends on how you define the word. Scientists observe and document same-sex behavior in horses regularly. What they don’t do is assign sexual orientation to animals, because orientation involves a consistent, internal preference that animals can’t self-report. The short answer: horses perform behaviors that look sexual between same-sex pairs, but the reasons behind those behaviors are more complex than simple attraction.
What Same-Sex Behavior Looks Like in Horses
Same-sex mounting is one of the most commonly observed behaviors, and it happens in both males and females. Young colts begin mounting other horses within the first few weeks of life, well before sexual maturity. Colts mount more frequently than fillies during play, and they also engage in more play-fighting. Fillies tend to focus on grooming and running. None of this early mounting involves ejaculation or reproductive function.
In adult stallions, same-sex mounting occurs most often in bachelor herds, where groups of males live together without mares. These all-male groups are a natural part of wild horse social structure, forming when young stallions leave their natal bands but haven’t yet acquired mares of their own. In these settings, mounting between stallions serves purposes that go well beyond sex.
Mares also mount other mares, though less frequently. When researchers studied 17 instances of mare-on-mare mounting, they found that 15 occurred when the mounting mare was in the follicular phase of her cycle, the fertile window just before ovulation. Every single mounting mare displayed pelvic thrusting, and more than half mounted multiple times. Some also exhibited behaviors typically associated with stallions: biting (44%), the lip-curling flehmen response (44%), and sniffing the other mare (11%). The mares being mounted were in heat and stood willingly, just as they would for a stallion.
Why Mares Mount Other Mares
The mare mounting studies revealed a hormonal pattern. Mares who mounted had significantly higher testosterone levels (about 17.7 pg/ml) compared to the mares being mounted (about 10.9 pg/ml). Researchers concluded that these transient spikes in testosterone were responsible for triggering stallion-like behavior in otherwise reproductively normal mares. No other abnormalities in their cycles, hormones, or anatomy were detected.
In rarer cases, persistent stallion-like behavior in mares has been linked to ovarian tumors that produce excess hormones. Large doses of estrogens, androgens, or anabolic steroids can also induce mounting behavior in mares. But the key finding is that occasional same-sex mounting happens in healthy, untreated mares as a natural, if uncommon, byproduct of normal hormonal fluctuations.
Social Functions of Same-Sex Behavior
Scientists have identified two main evolutionary explanations for why same-sex sexual behavior persists across mammals, including horses. The first is social bonding. Same-sex interactions, whether mounting, mutual grooming, or courtship-like displays, help animals form and maintain alliances, reconcile after conflicts, and strengthen group cohesion. Mutual grooming in horses is more frequent in larger, less stable groups, suggesting it plays an active role in reducing tension and regulating aggression.
The second explanation is dominance signaling. Mounting can communicate social status and reinforce hierarchies without the cost of actual fighting. By channeling competitive energy into courtship-like behavior rather than aggression, subordinate males may also gain indirect advantages, like sneaking access to mares when the dominant stallion is distracted. In bachelor herds, where establishing rank matters but outright combat is risky, mounting serves as a lower-stakes way to sort out who’s in charge.
Other contributing factors are simpler: practice for future mating, mistaken identity, or general arousal in exciting social situations. Masturbation is also considered normal behavior in horses, and colts that mount early in life show no reduction in fertility later. The behavior is part of healthy sexual development, not a sign of confusion or dysfunction.
Why Scientists Don’t Call Animals “Gay”
Human sexual orientation has two dimensions that don’t translate cleanly to animals: a consistent preference for partners of a particular sex, and a conscious identity built around that preference. In humans, these are clearly differentiated traits. Animals can’t communicate internal preferences, and their sexual behavior is far more context-dependent.
Same-sex behavior in animals is common across the animal kingdom, but it often increases when opposite-sex partners are unavailable, such as in captivity or in groups with skewed sex ratios. That doesn’t mean the behavior is purely a substitute. In some species, like bonobos and certain primates, same-sex interactions happen freely even when opposite-sex partners are present and clearly serve social rather than reproductive purposes. Horses fall somewhere in the middle: same-sex mounting happens in mixed groups too, but it’s far more frequent in single-sex settings like bachelor herds.
The distinction matters because “gay” implies a stable orientation, while what scientists document in horses is better described as same-sex sexual behavior. Some individual horses may show a stronger or more persistent tendency toward same-sex interactions than others, but without the ability to ask them about their preferences, researchers stick to describing what they observe rather than inferring why.
What Horse Owners Should Know
If your horse mounts or is mounted by a same-sex companion, it’s normal behavior with well-understood biological and social roots. It occurs in wild herds, domestic pastures, and breeding operations alike. In young horses, it’s part of play and development. In adults, it typically reflects social dynamics, hormonal shifts, or sexual energy without an available opposite-sex partner.
The one exception worth monitoring is a mare that displays persistent, intense stallion-like behavior, including frequent mounting, herding other horses, and aggressive posturing. While occasional mounting is driven by normal testosterone fluctuations, ongoing behavior of this kind can sometimes indicate an ovarian issue that a veterinarian should evaluate.