Friday Weird Science: Horsing Around and the Sexual Behavior of Stallions

May 20 2011 Published by under Friday Weird Science, Uncategorized

It all started with an innocent Tweet. Jennifer Ouellette (of the very fine Cocktail Party Physics blog and The Calculus Diaries fame), tweeted a link to this, a blog doing the history of electricity via inventions. The link was for the following device:

That, my friends, is an electrical device designed to prevent horses from MASTURBATING. And of course, this prompted Jennifer to note that she didn't know horses could DO that. I didn't know it either, though I would imagine that people who spend a lot of time around horses are pretty well aware.

Well of course, I looked it up. And I learned HOW horses masturbate (I mean, no hands!). And I often. Welcome to the sexual behavior of domestic stallions!

McDonnell et al. "Spontaneous erection and masturbation in equids." Journals of Reproduction and Fertility, 1991
McDonnell, S. "Stallion Sexual Behavior" (Chapter)
(And now we know why you may want to give Black Beauty some "private time" once in a while)

And if you either are an expert in this topic (ahem) or have other knowledge on this, please include in the comments. All I've got I've gotten from reading.

And from the videos below the fold. OH YES. You might not want to watch those while at work...yeah.

The way we breed horses now is not at all like while horses breed. In the wild, stallions (the guys) collect and fight over harems of ladies, and go through a complex series of behaviors to form and maintain their harems. Domestic stallions, on the other hand, are usually bred and training for specific things (from show to hunting and beyond), and then they are also...trained to breed. Sure, it's relatively easy to do, and often habit takes over, but you can run into problems when you have to get between the stallion and his lady to either take the semen for artificial insemination later, or for other purposes.

Normally, when a stallion gets wind of a mare, you get a specific pattern of behaviors:

Immediate interest and interaction with a mare in estrus
Erection within 2 minutes
Mount readiness. within 5-10 seconds after erection
Ejaculation on first mount
Total breeding time of 2-5 minutes

Yup. 2-5 minutes. That's all. Takes about 6-8 pelvic thrusts apparently, which is probably good as it doesn't look like horse hips were designed for a lot of thrusting. No word on what the mare thinks of this arrangement, but at least it appears effective. With domestic breeding, you can exposure the stallion to the mare (this is called teasing) and then train the stallion to hump a dummy for semen collection instead. I guess the stallions don't mind.

But of course, what about masturbation? How do they DO it? No hands, and their heads and spines aren't exactly flexible (you know, like dogs, or monkeys). Well it turns out, masturbation in horses is all about having a strong core (and you thought you did Pilates just for the aesthetics!). When the horse gets a spontaneous erection, they use their abdominal muscles to smack it up against their stomachs. Like this:

(The more you look at this the more you wonder what Catherine the Great was THINKING...)

This rarely results in ejaculation (it certainly doesn't seem very satisfying), but boy does it happen OFTEN. A stallion will pop wood about 18 times a day, and about 75% of those will result in masturbation (or maybe we're wrong and they're just waving them around in a stallion-y state of machismo). 18 times a day!

And if you think THEY are bad, check the donkeys. The first paper actually does a comparison, looking at instances of masturbation and spontaneous erections in stallions, vs donkeys, vs geldings (stallions that have had what makes them a stallion...snipped). Check it out:

You can see above the graph (I graph because I love!) of the number of spontaneous sexual behaviors (including mounting as the donkeys were in a free paddock, masturbation, and spontaneous erection) per day in the three sets of animals. And the donkeys hold strong! Coming in (heh) at an average of over 25 sexual behaviors in a 24 hour period. Poor gelding obviously don't really have as much libido, but they're still in there.

And not only are the equids prolific with their sexual behavior, they are early bloomers! Baby stallions can start exhibiting spontaneous erections when they are just ONE DAY OLD!

So what was the idea behold that old fashioned looking electrical invention? Well, much as masturbation has been maligned in humans, people didn't like to see it in their horses, either. It was considered a "stable vice" and thought to be the result of inactivity. People worried that it would impact the fertility of their horses. So they invented that thing. The idea is that it gets strapped on, and is mildly electrically charged, so that when the poor stallion tries to whack his penis up against his body...ZZZZRRTTT!!!


Luckily, papers on horse breeding and horse rearing today do NOT recommend putting a stop to horse masturbation. It's not known to have an effect on fertility, and much like human masturbation, has been shown to be a natural occurrence. In fact, that electrical device could very well have DECREASED the horse's mating abilities, as the horse would then learn that erections were very much a no no, and might have trouble mating in the heat of the event. So the next time you see a stallion, or a donkey, or even a gelding, waving his penis in the air like he just don't care, let him go free. It's totally natural, and given the kicking power of those legs, you probably don't want to get in the way...

12 responses so far

  • Kaija says:

    I worked on a farm with horses and cattle until I went off to university and yes, horse (and cattle and mammals in general) display a LOT of sexual behavior, as part of play and as individual amusement. Seems biology has a little lesson here for humans (especially the Puritanical North American kind...but I digress).

    One of the reasons that masturbation can be a "problem" with horses is that the horse can develop sore back muscles from all that self-humping, which can get in the way of that horse being able to "work", whether it's pulling a cart or a plow or carrying a rider. 🙂

  • WhizBANG! says:

    Gives a whole new illustration for the term "beating off." Although I guess the equines don't actually get off...but most humans don't literally beat.

  • seth says:

    Videos show the truth of the old English adage "he's hung like a jack donkey "

  • grrlscientist says:

    anyone who's been around horses knows this. (but i forget that most people haven't been around horses).

  • Huh. My geldings were definitely not that horny. But then, I suspect that this is a behavior that declines post-adolescence too. Anecdotally, I would say that young colts (uncastrated) or geldings under the age of about 3 years, get busy with themselves A LOT. Older geldings in training, not as much. Since most non-racing geldings (at least in the US) are castrated between 1-2 years of age, you could maybe attribute this decline to a decrease in circulating testosterone. Again, anecdote, but interesting.

    I am curious what else is included in "mating behaviors" besides spontaneous erection and masturbation. If it includes stereotypical male mating behaviors like "snaking" (they sling their head around in a particular way) or "halter tag" (biting other males' faces, rearing and pawing at each other with front legs and other play fighting) I would think that would account for a significant proportion of the "mating behaviors" attributed to geldings. It could be confounding though - those behaviors are not exclusively sexual behaviors - they also play a role in establishing and maintaining the social hierarchy within a herd.

    • scicurious says:

      For "mating behaviors" they included mating and mounting of females (because the donkeys weren't individually housed). That's all. The gelding data was ONLY masturbation and erections and did not vary between the ages of 2 and 25. The geldings are only 8 times a day though, and they noted that the vast majority of wood-poppin' occurred when the stable area was quiet and the horses were not distracted, so that could have something to do with it.

  • Leslie says:

    Just letting you know .. I got my education about horses here. ROFL

    Also, I think they ought to ban that device as cruel and unusual.

  • Coturnix says:

    The lore around horse farms is that the age-at-castration has much to do with it, i.e., those gelded very young (age 1-2) lose almost all of the sexual behaviors, while those who were sexually mature at the time of castration keep the entire range of behaviors, just not as frequent (or aggressive) as stallions.

  • Dr. H says:

    My gelding mounts the round hay bales in the pasture.

    He tries to mount my mares, but he pisses them off most of the time by food-guarding, they don't want anything to do with him. 😉

    In my experience, Coturnix's comment is correct, that if they are gelded early, they don't develop as much sexual behavior. The masculine characteristics don't much develop either. For example, if a male is gelded "late", he often develops a thicker neck with a 'crest' at the topline. If he is gelded early, his neck often develops normally, much like a mare's. I assume that it has to do with the amount of testosterone present during growth.

  • onemoment says:

    One thing people don't seem to know is that horses do sometimes ejaculate when they masturbate on their own. i've seen it a few times, and they sure make a mess on their front legs.

  • horsey says:

    I used to know a gelding who loved having his sheath rubbed

  • doggy one says:

    on the other hand,i used to know a male german shepherd who loved to be "helped out"

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