Courtship and Reproduction

A stallion checks a mare in estrus. She is welcoming him with her back legs spread, her tail lifted, and her ears back.1


If you are a gelding, you may skip this chapter.

Gelding (castrating) a mule using an emasculator.2 Gelding has been fashionable since the Iron Age,3 thousands of years before the invention of anesthesia or pain killers. This is the source of “Rocky Mountain Oysters”.4 I’m sure this doesn’t hurt a bit.


When fillies and colts have a chance to romp together, they develop the skills for “doin’ what comes natur’lly”.5 When foals play with adult horses, they will often mount the adults.6 This is not perverted. It is normal for ungulates7 — animals with hooves. What happens if a foal does not get such opportunity? Heterosexual contact during childhood has been found to be critical for the organization of copulatory activity in rams8. Dogs who have experienced early social isolation do not have normal coital behavior.9 The same might be expected in horses. Dogs, rams, stallions, and likely all mammals benefit for early opportunities to develop critical social skills, and likely less socially capable if kept isolated as youngsters. I would like to live in a world in which horses, mules, and donkeys all could stay with their herd until the age of 4, never locked in a stall, and never ridden. We’d find them better at many social behaviors, including doin’ what comes natur’lly.

Stallions are from Mars, Mares are from Venus

“’The single most important difference between the sexes is the difference in their investment in offspring. The general truth is this: females do all the investing; males do none of it.’ (Trivers10 1985, p. 207) Although Trivers’ general rule has many exceptions, it accurately identifies the primary source of conflict between the sexes: in most sexual organisms, most of the energy and time invested in offspring comes from females. From this basic fact it follows that, for males more than females, reproductive success is limited by the number of matings with fertile partners. For females more than males, on the other hand, reproductive success is limited by the time and effort required to garner and transfer energy to offspring and to protect and care for them. Males therefore are usually more eager than females to mate at any time with any partner who may be fertile, while females are usually more careful than males to choose mates who seem likely to provide good genes, protection, parental care, or resources in addition to gametes. Combined with female interest in mate quality, male interest in mate quantity creates a widespread conflict of interest between the sexes.11” But I guess you knew that.

The forces that Trivers identifies operate when a feral stallion assembles his band. He strives for the greatest number of mares in it. The mares may or may not agree to join, and may find another band they would prefer to belong to. But within an established band, courtship in horses is more egalitarian than Trivers suggests it should be.

Stallion and mare both play an active role in courtship. Both stallions and mares may be the initiators of courtship. Who initiates may be influenced by their condition (readiness to breed) and their experience.

Timing is everything

Timing the sexual interest of all has a survival value: when all foals are born at about the same time, some have a better chance of surviving predation than if they come along one at a time. Female estrus is brought on when the days begin to lengthen (the spring), and likely also by other factors, such as the condition of the other females. Because it is the lengthening day that triggers love in horses, they are considered long-day breeders, along with ring-tailed lemurs, hamsters, groundhogs, and minks. (Fall conception, favored by sheep, goats, foxes, red deer, elk, and moose, makes those species short day breeders.)

Changes in day length (both longer and shorter) can be sensed by most species of plant and animal. In horses and humans, melatonin plays a role.12 And horses, like chickens, can be tricked into coming into heat earlier in the year, using an invention that Thomas Edison takes credit for.

Hormones also play a large role in mating. There is evidence in other species that estrus hormones brings on sexual interest and activity on the part of quiescent males13, and that androgen in males helps with estrus (or ovulatory) synchronization — getting the ladies to all come into heat at once.14 It seems likely that this is true in horses, too. Synchronization is critical, because estrus only lasts 5-7 days for the mare. When she is in estrus, she repeatedly approaches the stallion, urinates frequently, moves her tail away to expose the perineum, and stands still with her back legs spread. But when estrus ends — diestrus — she walks away from approaching stallions, and will squeal, strike, and kick to keep him away. A stallion must strike while the iron is hot.

Estrus in a mare helps bring on estrus in other mares, and synchrony of estrus across the mares of a band is important for foal survival. Those conceived at the same time are born at almost exactly the same time. As I said, a surge of foals all at the same time helps overwhelm local predators, who simply can’t eat them all at once.

And there is another benefit to this timing: horses have a strong paternal skew (one stallion gets dates with more than one mare.) By coming into estrus at the same time, the mares in his band make life more difficult for him, because he can’t defend them all (from other stallions) at the same time.15 Ovulatory synchrony spreads the wealth, by preventing the lead stallion from monopolizing access to them, and giving some of the other males in the herd an opportunity. As a result, the genetic diversity of the band is improved. The dominant stallion is not the father of all.

Everyone wants to have their babies in the spring at the start of a brief period of abundant grass and mild weather, so generally short day breeders have shorter gestation periods than long-day breeders. (For example, a moose cow has a gestation period of about 8 months, so if Mrs. Moose conceives four months after Mrs. Horse, they both have their babies in the spring.) Pregnancy in mares lasts nearly a year, so horses conceived in the spring are born the next spring.

Courtship and reproduction in horses is nearly identical to that of elephants, cattle, and other social grazers. And as with other social grazers, any of the behaviors of courtship may occur throughout the year, but usually not in the sequence of courtship. Young geldings, for instance, may mount each other after rough play, and some of a mare’s estrus behaviors may occur when she is not in estrus.


In a band of feral horses, there may be two or more stallions in a herd. While one stallion will be dominant, mares may be willing to breed with any of the stallions present. When a dominant stallion catches a mare with another stallion, one study16 found that his approach with the arched neck threat (see the chapter on Fighting) is sufficient to cause the other to dismount, and that fights never occurred.

Mares in a feral band do not breed only with stallions from their band, and so stallions from a band will sometimes breed with mares from other bands.

Dominance increases the odds of paternity, but does not guarantee it. In a study of feral horses in Alberta, dominant males accounted for only 5 of 8 copulations observed;17 in a study of feral horses in New Mexico,18 they accounted for 17 of 19. In herds with multiple stallions, dominant stallions bred in 49% of the 81 matings observed, subordinates bred in 42% of them, and males from other bands bred in 9%.19

Wild horses may be involved in several different “breeding systems” if there are multiple stallions in the band:20

  • several males breeding serially with one mare within a band (in one observation, three different stallions bred with one mare in 5 minutes.)
  • consort pair formation (a stallion guards a single mare who only breed with each other)
  • nearly exclusive breeding by the dominant male.

Just which breeding system is in place may depend on the dominant male. In many species, pheromones appear to help regulate the onset of estrus, and when several mares are in heat, this must have consequences on which breeding system is found.

Mares add some complexity to the paternity questions. In one study, 13 mares out of 22 were observed being mounted by more than one stallion. Nine of the 22 were observed breeding more than four times, and of those 9, 6 were bred by two or more males.21 Since mares are quite able to refuse a suitor (see below), this polyandry must be her idea. Multiple suitors improves the genetic diversity of the band, which is in the species’ best interest.

The Courtship Sequence

Stallion courtship begins with seasonal changes in his testosterone level, increasing his deep interests in the ladies and their scents. He spends lots of time monitoring their condition by both following them and smelling their urine and dung. Breeding condition is a two-way street. If he is ready, she is influenced to hurry up, and vice versa. Through hormones and day length, the schedules coordinate for the convenience of all.

As things heat up, and she comes into estrus (a brief period of sexual receptivity, in which she is fertile), he increases his tending — herding without the directional drive — and follows her everywhere. He may herd her in circles, or away from the band or another stallion.22 Until she reaches estrus, she will walk away as he approaches, and they’ll play follow the leader until she is annoyed or he gets the hint. Tending is sometimes called “leadership”, but when it drives others in circles or away from the band, it seems more like aggression.23

The onset of estrus brings on many changes in the mare’s behavior. She will urinate frequently, in small quantities. This urine is loaded with volatile (easily evaporated) compounds that become airborne, and signal her condition to those with a knowledgeable nose. In addition, she may engage in clitoral winking — rapid, rhythmic eversion of the genital labia and rhythmic contractions of her vagina that flash the red color of what’s inside. Winking is often done with her spreading her back legs slightly, and squatting a bit, and is sometimes accompanied by urination. You can see the effect in a photo in the section on Rolling.

The mare may assume a submissive expression: lips pulled back, head and neck stretched low.

As she hits estrus, he will continue his tending and is likely to sample the air frequently with his flehmen response. The flehmen response occurs much more often when an estrus mare is present than when the nearby mares are diestrus (not in estrus).24

As she becomes more interested in the project, she may slow, allowing him to approach and make contact. She may lift her tail, possibly turning to face him, then turn so that her rump with tail lifted is near his face. In many species of equid,25 the estrus posture includes holding the head low, pulling the lips and ears back, and spreading her back legs, but you may or may not see these things.

In the pair below, she grazes with her posterior near his face, and tail lifted. He checks conditions with his flehmen response.

Flehmen response in this feral horse stallion is displayed by the stretched neck and raised, inverted upper lip. This posture is a response to particularly exciting chemicals and olfactory signals that are detected by the main olfactory epithelium and concentrated directly into the vomeronasal organ, which in part guides sexual activity.26 The Flehmen response was the move that Mr. Ed used when he talked.27

When permitted by an estrus mare, a stallion may rub his head on her flanks or rest his chin on her back. He may groom her neck, flanks, and rump before mounting. His penis will extend out of the prepuce, as shown in the photo below.

A feral horse stallion is exhibiting penis extension and rubbing of the female’s flanks as part of the male reproductive behavior sequence.28 If no female is adjacent, penis drop usually is a comfort, rather than sexual, behavior.


Girls Rule

If the stallion gets ahead of his skis, and she is not ready, she may kick him. In one study, all attempts by mares to drive off an aggressive stallion were done by hind leg kicks or threats to kick.29 Such kicks may be forceful, depending on his skiing skills. Small hops with her back end, as if threatening to kick, may be part of foreplay, not a signal to go away.30 A disinterested mare is likely to use her back end in self defense simply because that is the part of her that is closest to the stallion she is trying to avoid.

Mares are successful at preventing insemination. In one study, when a male mounted but did not gain intromission, it was almost always because of aggression by the female, usually with kicks from her back legs.31 Forced copulation is one way that males of some species (such as mallard ducks and dolphins) ensure paternity, but one thorough study32 found absolutely no evidence of this in a herd of feral horses.33 Mares can just say “no!”, and thus have a key role in mate selection.


At this point, if both contestants are so inclined, he may mount her from behind, using his front legs on her sides to hang on. He extends his head forward and down, so that his mouth is near her neck. As with other birds and mammals, she supports much of his weight.

There are many possible outcomes of his attempt to mount. Copulation might be successful. She might change her mind, kick and walk off. She might not be in the mood and try to ignore his advances. She might have a headache. We’ve all been there.

The position of the stallions mouth in the photo below is interesting. When desert tortoises do this, the male bites the female on the neck, which she apparently finds arousing. In mammals such as the spotted seal,34 Richardson’s ground squirrel,35 coyotes,36 and red fox,37 biting occurs before or during intercourse. In some equids, such as the African wild ass, stallions bite the mare’s neck during intercourse.38 In our domestic horse, the stallion seems to reach for the neck but not take a bite.


Successful copulation is occurring between this feral stallion and mare. This reproductive behavior is characterized by a maintained mounting position on the female for the male and a relatively stationary, relaxed position for the female. Unsuccessful copulation is often a result of mare rejection, with the female expressing agonistic behaviors such as kicking toward the male and only a brief mounting position for the male.39

Once is not always enough. Copulation may occur from one to three times, which helps ensure good results.


Pregnancy lasts nearly a year — between 320 and 370 days. During this time, the mare must increasingly eat for two. She needs critical trace elements, such as copper, to build a healthy baby, and plenty of energy. Such requirements continue after giving birth, to help her recover and deal with the demands of lactation.


If all has gone well, the mare will give birth the next spring. Like deer, elk, elephants, and many other social species of mammals, she prefers solitude for her last few days of pregnancy. Mares usually foal at night or in the early morning. Labor usually takes less than half an hour, with the entire foal emerging about 15-20 minutes after his feet have appeared. As soon as he is born, his mother begins licking him. This may be an instinct, but it is also likely that it tastes good, The licking and grooming she gives helps replace salts and fluid that she has lost in her final hours. It stimulates the foal, and seems to help start his engine. It helps clean up the foal and leave him almost odorless, less likely to attract predators. It brings her nose close to his body, and helps her learn his scent. And it builds and strengthens a bond between foal and mare. Oxytocin surges during labor, and helps to create a powerful bond between the two.

Young horses are precocial, like all grazing animals: within minutes of birth they can stand, and in a few minutes more they take their first steps, walk, and try running. This is critical for the survival of the species, because foals must look like cheeseburgers to any passing predators. Predation might kill half of all foals in their first year, or fewer if predators are scarce. (Humans are altricial — born helpless, and remaining that way until kicked out of the house. Somehow human kids survive.) By the age of one week, foals have begun to associate with other foals and to form peer groups.40

In a later chapter on “Early Learning and Imprinting”, I tell you some remarkable stories about a mule deer, a turtle, a snake, and a cockatiel. Horses are like mule deer, turtles, and snakes: they are precocial. Humans and cockatiels are altricial. But I believe all can learn before birth.


Unlike many other hoofed animals, where the male loves them then leaves them, a band of horses stays together year round. Females seem to form the glue for this, keeping the stallion(s) interested by periodically showing estrous behavior without ovulating. And love is all mixed in: mares and stallions with long-term social relationships will often rest together, graze together, and groom each other — all without sex.41 Pretty cool, huh?


Both male and female birds masturbate.42 Both male and female dogs masturbate.43 Gibbons masturbate.44 Racing camels masturbate.45 Chimpanzees masturbate.46 Japanese Macaques masturbate.47 Cattle masturbate.48 Cats masturbate.49 Chinchillas, rats, porcupines, walruses, squirrels, penguins, porcupines, elephants, and dolphins masturbate.50 Masturbation is not diabolical, not an evil of the flesh, not disobedience to the Lord, not decadent. It does not result in warts or blindness. Masturbation is pleasurable, and relieves tension in both males and females.

Horses masturbate. Masturbation in a stallion is a rhythmic bouncing, pressing, or sliding of an erect penis against the abdomen. There are some people that believe that humans should be allowed to do this, but that stallions should not. And some who believe that no animal should ever be allowed to do this disgusting thing. And there who tell us they are only concerned that masturbation will lower a stallion’s sperm count. (Ejaculation rarely accompanies masturbation in stallions, so this concern is silly. And note that it doesn’t seem to hurt reproduction in feral herds!) Stallions masturbate. Geldings masturbate. Mares masturbate. Spontaneous erection and masturbation occur at the same rate as in other equids, at about one episode every 90 min. This behavior is independent of environment, housing, exposure to breeding, or age.51 It is not influenced by frustration or boredom.52

A typical comfort behavior for feral horse males is masturbation, which is expressed when a horse flexes his erect penis against his abdomen. This behavior is not expressed in conjunction with a nearby female and should not be confused with the penis drop observed when a male is reproductively tending a female.53

Preventing masturbation. The facts of life have only been seen, by some, as an obstacle to be overcome. One authority teaches “Many stallions fall into the habit of masturbation. Prevention is far better than cure… Once the habit is contracted it is practically impossible to put a stop to it.54” He recommends removing all bedding from the horse’s stall, and then staying with him for eight to ten hours. Folks have devised all sort of gadgets to prevent masturbation in horses, including stallion rings, brushes, cages, and shock devices. The US Patent and Trademark Office (USPTO) issues a patent for an electrical device back in 1894, and has since issued a number of such patents.

An electrical device to prevent masturbation in stallions. Patented in 1894.55

Masturbation is not a stall vice. It occurs in horses everywhere — we just happen to see it in stalls. And it is not a vice. It is natural.


1 Image source:

2 Image source:

3 Levine, M. A., Bailey, G.N. & Whitwell, K., et al. (2000). “Paleopathology and horse domestication: the case of some Iron Age horses from the Altai Mountains, Siberia” in G.N. Bailey, R. Charles & N. Winder (Eds.) Human Ecodynamics and Environmental Archaeology (pp. 123–33). Oxford: Oxbow.

4 a dish made of testicles. “The organs are often deep-fried after being peeled, coated in flour, pepper and salt, and sometimes pounded flat. This delicacy is most often served as an appetizer with a cocktail sauce dip.” — “Rocky Mountain oysters” Wikipedia

5 See the lyrics to this delightful song here:

6 Crowell-Davis, Sharon L., Katherine A. Houpt, and L. Kane. “Play development in Welsh pony (Equus caballus) foals.” Applied Animal Behaviour Science 18, no. 2 (1987): 119-131.

7 Moore, A.V., 1968. Effects of modified maternal care in the sheep and goat. In: G. Newton and S. Levine {Editors), Early Experience and Behavior, Vol. 15. C. Thomas, Springfield, IL, pp. 481-529.; Orgeur, P. and Signoret, J.P., 1984. Sexual play and its functional significance in the domestic sheep {Ovis aries L.). Physiol. Behav., 33: 111-118.; Tyler, S.J., 1972. The behaviour and social organization of the New Forest ponies. Anim. Behav. Monogr., 5: 85-196.

8 Orgeur, P. and Signoret, J.P., 1984. Sexual play and its functional significance in the domestic

sheep {Ovis aries L.). Physiol. Behav., 33: 111-118.

9 Beach, F.A., 1968. Coital behavior in dogs. III. Effects of early isolation on mating in males.

Behaviour, 30: 217-238.

10 Trivers, Robert. “Social evolution.” (1985).

11 Smuts, Barbara B., and Robert W. Smuts. “Male aggression and sexual coercion of females in nonhuman primates and other mammals: evidence and theoretical implications.” Advances in the Study of Behavior 22, no. 22 (1993): 1-63.

12 For a review of the role of melatonin in reproduction see Tamarkin, Lawrence, Curtis J. Baird, and O. F. X. Almeida. “Melatonin: a coordinating signal for mammalian reproduction.” Science 227 (1985): 714-721.

13 Vandenbergh, John G. “Endocrine coordination in monkeys: Male sexual responses to the female.” Physiology & Behavior 4.2 (1969): 261-264.

14 Dodge, James C., Mark B. Kristal, and Lori L. Badura. “Male-induced estrus synchronization in the female Siberian hamster (Phodopus sungorus sungorus).” Physiology & behavior 77.2 (2002): 227-231.

15 “Reproductive synchrony”

16 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

17 Salter, K. E. (1978): Ecology of feral horsea in Western Alberta. M. S. Thesis, Univ. of Alberta, Edmonton. Cited in Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

18 Nelson, K.J. (1978): On the question of male limited population growth in feral horses (Equuis caballus). M. S. Thesis, New Mexico State Univ., Las Cruces. Cited in Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

19 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

20 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

21 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

22 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

23 This view is taken by Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

24 This is likely true across all species that demonstrate the response. For buffalo, see

Rajanarayanan, Swamynathan, and Govindaraju Archunan. “Occurrence of flehmen in male buffaloes (Bubalus bubalis) with special reference to estrus.” Theriogenology 61, no. 5 (2004): 861-866.

25 Ransom, Jason I., and Petra Kaczensky. Wild Equids: Ecology, Management, and Conservation. JHU Press, 2016.

26 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009)

27 Watch a YouTube video to see Mr. Ed talking. There are several, such as this: “Clint Eastwood Meets Mister Ed – 1 of 2 (Captioned)”

28 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009)

29 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

30 Ransom, Jason I., and Petra Kaczensky. Wild Equids: Ecology, Management, and Conservation. JHU Press, 2016.

31 Miller, Richard. “Male aggression, dominance and breeding behavior in Red Desert feral horses.” Ethology 57, no. 3‐4 (1981): 340-351.

32 Kirkpatrick, J. F., and J. W. Turner. “Changes in herd stallions among feral horse bands and the absence of forced copulation and induced abortion.” Behavioral ecology and sociobiology 29, no. 3 (1991): 217-219.

33 Another study (Berger, Joel. “Induced abortion and social factors in wild horses.” (1983): 59-61.) reported forced copulation was common when a new stallion took over a band, and that it often led to miscarriage (which the author called “abortion”). Kirkpatrick and Turner analyze the possible methodological weaknesses of this previous study. See Kirkpatrick, J. F., and J. W. Turner. “Changes in herd stallions among feral horse bands and the absence of forced copulation and induced abortion.” Behavioral ecology and sociobiology 29, no. 3 (1991): 217-219.

34 Beier, John C., and Douglas Wartzok. “Mating behaviour of captive spotted seals (Phoca largha).” Animal Behaviour 27 (1979): 772-781.

35 Davis, Lloyd S. “Copulatory behaviour of Richardson’s ground squirrels (Spermophilus richardsonii) in the wild.” Canadian Journal of zoology 60, no. 11 (1982): 2953-2955.

36 Bekoff, Marc, and Judy Diamond. “Precopulatory and copulatory behavior in coyotes.” Journal of Mammalogy 57, no. 2 (1976): 372-375.

37 Bijlsma, Rob G. “Copulatory lock of wild red fox (Vulpes vulpes) in broad daylight” Lutra 2014 57 (1) 37-38

38 Pagan, O., F. Von Houwald, C. Wenker, and B. L. Steck. “Husbandry and breeding of Somali wild ass Equus africanus somalicus at Basel Zoo, Switzerland1.” International Zoo Yearbook 43, no. 1 (2009): 198-211.

39 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009)

40 Goodwin, Deborah. “The importance of ethology in understanding the behaviour of the horse.” Equine Veterinary Journal 28 (1999): 15-19.

41 Crowell-Davis, Sharon L. “Sexual behavior of mares.” Hormones and Behavior 52, no. 1 (2007): 12-17.

42 My wife and I have 7 cockatiels who are not clipped, live in an aviary next to our office, and are sometimes allowed to come in to the office. They like to sit on my head, shoulders, knee, and top of my monitor. One day recently I had a male cockatiel who masturbated on my head, and then a female who masturbated on my shoulder. The movements of both sexes are quite similar.

43 Mertens, Petra A. “Reproductive and sexual behavioral problems in dogs.” Theriogenology 66, no. 3 (2006): 606-609.

44 Mootnick, Alan R., and Elaine Baker. “Masturbation in captive Hylobates (gibbons).” Zoo Biology 13, no. 4 (1994): 345-353.

45 Tinson, A. H., Kuhad, K. S., Singh, K., & Al-Masri, J. (2000). Surgical technique to control sand masturbation in male racing camels. Journal of Camel Practice and Research, 7(2), 167-169. See also Tanwar, R. K., and Anju Chahar. “Urethritis associated with sand masturbation in male camels.” Intas Polivet 5, no. 2 (2004).

46 Marson, J., S. Meuris, F. Moysan, D. Gervais, R. W. Cooper, and P. Jouannet. “Cellular and biochemical characteristics of semen obtained from pubertal chimpanzees by masturbation.” Journal of reproduction and fertility 82, no. 1 (1988): 199-207.

47 Thomsen, Ruth, and Joseph Soltis. “Male masturbation in free-ranging Japanese macaques.” International journal of primatology 25, no. 5 (2004): 1033-1041.

48 Perumal, P., K. Vupru, K. Khate, M. Veeraselvam, Atul Kumar Verma, A. K. Nahak, and C. Rajkhowa. “Spontaneous erection and masturbation in mithun (Bos frontalis) bulls.” International journal of Bio-resource and Stress Management 4, no. 4 (2013): 645-647.

49 Schwartz, S. “Use of cyproheptadine to control urine spraying and masturbation in a cat.” Journal of the American Veterinary Medical Association 214, no. 3 (1999): 369-71.

50 LoPiccolo, Joseph, and W. Charles Lobitz. “The role of masturbation in the treatment of orgasmic dysfunction.” Archives of Sexual Behavior 2, no. 2 (1972): 163-171.; “Self-love in the animal kingdom”

51 McDonnell, S.M., Henry, M., Bristol, F., 1991. Spontaneous erection and masturbation in equids. J. Reprod.

Fertil. 44, 664–665, Suppl.

52 Darling, Kjersten, and James M. Giffin. Veterinary guide to horse breeding. Lulu Press, Inc, 2014.

53 image source: Ransom, Jason I., and Brian S. Cade. “Quantifying Equid Behavior–A Research Ethogram for Free-Roaming Feral Horses.” U.S. Geological Survey Techniques and Methods 2-A9, 23 p. (2009)

54 Johnstone, James Hope Stewart. The Horse Book: a practical treatise on the American horse breeding industry as allied to the farm. Sanders Publishing Company, 1908. p. 68.

55 Image source:


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