Fact-checked by Grok 2 weeks ago

Stallion

''Stallion'' may refer to: For the animal, see [[Stallion]]. [If this is the disambiguation page, the above structure applies; otherwise, for the horse article intro:] A '''stallion''' is a male [[horse]] that has not been [[Gelding|gelded]] (castrated). Stallions follow the conformation and anatomy of the species, but are built for greater muscular endurance, enabling them to engage in activities requiring strength and speed, such as breeding or competitive sports. Typically, a stallion's temperament is more assertive and energetic compared to that of a [[mare]] or [[gelding]], influenced by higher testosterone levels. Stallions are primarily valued for their role in [[horse breeding]], where selective breeding enhances desirable traits in offspring. The term originates from Old English "stallion," meaning a male horse kept for breeding. [Note: Adapted from standard encyclopedic definition; in real editing, use reliable sources like veterinary texts.]

Definition and Characteristics

Physical Distinctions

Stallions are adult male horses (Equus caballus) that have not been castrated, distinguishing them physically from mares and geldings through pronounced sexual dimorphism. These traits arise primarily from elevated testosterone levels, which promote greater overall body size, heavier muscling, and prominent secondary sexual characteristics. In breeds like the Mangalarga Marchador, stallions demonstrate significantly larger dimensions in most linear measurements, including height at the withers, body length, and limb proportions, compared to mares, underscoring their robust build.^[1] A key visible distinction is the crested neck, where testosterone drives substantial muscle development along the nuchal ligament, creating a thickened, arched profile and denser mane. This muscular crest enhances the stallion's imposing appearance and is more exaggerated than in females or castrated males, reflecting androgen-mediated growth in the neck and shoulder regions.^[2] Stallion height at the withers typically ranges from 14 to 17 hands (56 to 68 inches), with weights averaging 900 to 1,200 pounds, though these metrics vary by breed and management. Thoroughbred stallions, bred for racing, average over 16 hands, while Arabian stallions are smaller at 14.1 to 15.1 hands, emphasizing endurance over speed.^[3]^[4]^[5] Heavier muscling in the chest and forequarters supports broader thoracic dimensions, facilitating expanded lung capacity for sustained exertion, while leg and hoof structures feature strong pastern angles and resilient hooves adapted for propulsion and terrain traversal.^[6]

Age Classification and Development

Stallions are classified as colts until approximately four years of age, after which they are considered mature stallions.^[7] Sexual maturity, marked by the onset of viable sperm production and breeding capability, is typically reached between 15 and 18 months, though full reproductive development may extend to 2-3 years depending on the individual and breed.^[8] Full physical maturity, encompassing skeletal completion and muscular development, generally occurs between 5 and 7 years, with some breeds requiring longer.^[9] The growth phases of stallions begin with rapid skeletal development in the first year, during which foals achieve about 80% of their mature height and roughly 43% of their adult weight by six months, often doubling their birth weight within the initial three months through high milk intake and daily gains of 2-3 pounds.^[10] Muscle maturation accelerates during puberty due to a surge in testosterone concentrations, which rise sharply around 15-18 months and stabilize thereafter, promoting secondary sexual characteristics and overall body composition changes.^[11] Key developmental milestones include testicular descent, which begins in utero around 270-300 days of gestation and is typically complete by four weeks post-birth in most cases.^[12] First erections and mounting behaviors often emerge around one year of age as puberty approaches.^[13] Peak fertility is typically attained between 5 and 8 years of age, coinciding with optimal semen quality and libido before any age-related decline.^[14] Breed-specific variations influence these timelines, with draft breeds such as Clydesdales or Percherons maturing more slowly and potentially not reaching full physical development until 7-8 years due to their larger size, compared to light breeds like Thoroughbreds or Quarter Horses, which typically mature by 5-6 years.^[15]

Anatomy and Physiology

Reproductive Anatomy

The reproductive anatomy of the stallion is adapted for efficient sperm production, storage, and delivery during copulation. The external genitalia include the penis, prepuce, and scrotum. The penis is a fibroelastic organ measuring approximately 50 cm in length when flaccid, with a diameter of 2.5 to 6 cm, and extends to 75-100 cm in length and 6-8 cm in diameter when erect, facilitating intromission.^[16] The prepuce, or sheath, consists of an external fold and internal layer that envelops the penis when retracted, protecting it from injury and debris.^[17] The scrotum houses the testes and is supported by the tunica dartos, which regulates temperature for spermatogenesis by contracting or relaxing in response to environmental conditions.^[17] Internally, the testes are paired oval structures located within the scrotum, each typically weighing 150-250 g in mature stallions and producing 5-11 billion sperm cells daily through spermatogenesis in the seminiferous tubules.^[18] The epididymis, attached to each testis, consists of a head, body, and tail where sperm mature and are stored; the tail connects to the ductus deferens, which transports sperm to the urethra.^[17] Accessory sex glands contribute to semen composition: the seminal vesicles (vesicular glands) produce fluid rich in sugars for sperm energy, the prostate surrounds the urethra and secretes antimicrobial substances, and the bulbourethral glands add viscous mucus to semen, resulting in a gel-free ejaculate volume of 30-100 mL containing 1-10 billion sperm.^[19]^[20] Hormonal regulation is centered in the testes, where Leydig cells produce testosterone at blood concentrations typically ranging from 1-4 ng/mL, peaking during the breeding season to support libido, spermatogenesis, and secondary sexual characteristics.^[21] Follicle-stimulating hormone (FSH) and luteinizing hormone (LH), secreted by the anterior pituitary in response to gonadotropin-releasing hormone (GnRH), stimulate Sertoli cells for sperm development and Leydig cells for testosterone synthesis, respectively, with levels fluctuating seasonally.^[22]^[23] Unique anatomical features enhance functionality and protection. The retractor penis muscle, a paired smooth muscle band, pulls the penis into the prepuce when not erect, preventing trauma.^[17] The urethral diverticulum, a pouch at the junction of the pelvic and penile urethra, allows separation of urine and semen during ejaculation, reducing contamination risks.^[17]

Muscular and Skeletal Adaptations

Stallions display enhanced muscular development compared to mares, particularly in the hindquarters, where androgen hormones promote a higher proportion of fast-twitch muscle fibers for explosive power. In Thoroughbreds, the percentage of Type IIA fast-twitch oxidative fibers increases with age to 53% in adult stallions, compared to 45% in adult mares, representing up to an 8% greater proportion in stallions overall, though breed-specific variations can reach 20% differences in fast-twitch composition.^[24] This androgen-influenced adaptation supports rapid acceleration and strength in both wild territorial behaviors and domestic performance roles.^[25] Skeletal features differ by sex; mares typically have a wider pelvic inlet for reproduction, while stallions exhibit robust pelvic support for hindquarter musculature. Cannon bones in fore and hind limbs are of similar length, enhancing stride efficiency.^[26] Bone mineral density in metacarpals typically ranges from 1.2 to 1.5 g/cm², though no significant sex differences are consistently reported across studies.^[27] Cardiovascular and respiratory systems in horses feature hearts comprising approximately 1% of body weight (0.8-1.2% range)—about 5 kg for a 500 kg horse—and lung capacity up to 50-55 liters, enabling sustained high-intensity activity. Tidal volume at rest is about 5 liters, increasing to 10 liters during exercise, with minute ventilation reaching 1,400 liters per minute at peak effort to meet oxygen demands.^[28]^[29] Adaptations for survival include thicker dermal collagen layers compared to humans and sex-influenced fat distribution patterns, such as cresty neck fat in stallions, aiding thermoregulation and mobility in varied environments.^[30]^[31]

Herd Behavior

In natural and semi-natural environments, stallions typically form social groups known as bachelor bands, consisting of 2 to 10 unattached males, often young colts expelled from their natal family groups or older stallions who have lost their harems.^[32]^[33] These bands provide opportunities for social learning through play-fighting and dominance practice, preparing members for future harem acquisition, with dominant individuals in the band often challenging established stallions to steal mares by around age 5.^[32] In contrast, successful dominant stallions lead stable family groups, or harems, comprising one stallion, 2 to 20 mares, and their dependent foals, where the stallion maintains control to protect and breed within the unit.^[33]^[34] Within these groups, hierarchies are established and maintained primarily through aggressive displays rather than constant physical combat, ensuring efficient resource access and group cohesion. Stallions assert dominance via rearing on hind legs, striking with forelegs, and biting at rivals or subordinates, often escalating to chasing if initial threats like pinned ears or snaking postures fail.^[35]^[36] Submission is signaled by subordinates lowering their heads, averting gaze, or fleeing the aggressor, minimizing injury and reinforcing the linear rank order where higher-ranking stallions secure priority in movement and protection roles.^[37]^[33] In bachelor bands, older males typically dominate younger ones through these interactions, while in family groups, the stallion's authority is subordinate to the lead mare's influence on group decisions but paramount in defending against external threats.^[32] Daily routines in stallion-led groups revolve around foraging and survival, with the dominant stallion often directing movement to grazing areas and water sources while deferring to the lead mare for optimal resource selection.^[33] Herds travel in single file, spending much of the day grazing collectively, followed by resting and mutual grooming to strengthen bonds.^[32] For predator defense, stallions position themselves peripherally, herding the group away from threats or forming protective formations such as circles around vulnerable foals, charging intruders with strikes or kicks to deter attacks.^[35]^[38] Seasonal dynamics intensify stallion aggression, particularly during the breeding season in spring and summer, when testosterone levels rise, leading to heightened challenges from bachelor stallions and increased territorial patrols within harems.^[33] This period sees more frequent displays and minor skirmishes to reaffirm hierarchies, though severe fights are rare due to risk of injury.^[35] Concurrently, young colts are dispersed from family groups at 2 to 3 years of age, driven by the resident stallion to prevent inbreeding and reduce intra-male competition, prompting them to join bachelor bands where social bonds form away from kin.^[34]^[32]

Mating and Territorial Displays

Stallions engage in elaborate courtship rituals to attract and assess receptive mares, primarily during the breeding season. A key behavior is the flehmen response, where the stallion curls his upper lip and exposes his teeth upon detecting pheromones in a mare's urine or vaginal secretions, enhancing olfactory analysis via the vomeronasal organ.^[39] This is often followed by nuzzling, involving gentle sniffing, nibbling, and licking along the mare's body from the shoulders to the perineum, which stimulates her and confirms estrus.^[39] Vocalizations such as soft nickers accompany nose-to-nose contact, while mounting attempts—sometimes without full erection—escalate as precopulatory displays to test the mare's readiness.^[39] Territorial defense is crucial for maintaining breeding rights, with stallions employing scent-marking to delineate boundaries and deter rivals. Urine marking involves overmarking mare feces or urine to advertise paternity and discourage intruders, often sniffed before deposition but not after.^[40] Dung piles, known as "stud piles," form through repeated defecation in strategic locations like herd routes, where harem-holding stallions mark and sniff them to reinforce territorial claims without direct confrontation.^[40] If chemical signals fail, physical fights ensue, featuring aggressive charges, kicks, and bites aimed at repelling challengers seeking to usurp the harem.^[41] Once a harem is established, the dominant stallion actively guards his mares to prevent rival access and ensure his reproductive success. Herding involves nipping at the flanks or hocks to reposition mares, keeping them close—often within 2 mare lengths—and away from potential threats, with intensity peaking upon introduction of new females or environmental changes.^[39]^[42] Post-copulation, the stallion remains vigilant nearby for several minutes, monitoring the mare to block immediate re-breeding by outsiders, a behavior that extends year-round but heightens during estrus.^[39] In wild herds, these displays contribute to high reproductive skew, where dominant stallions sire 60-70% of foals in intact harems, as non-harem males account for only 15-33% through opportunistic matings.^[43]^[44]

Reproduction and Breeding

Natural Reproductive Cycle

The natural reproductive cycle of stallions is characterized by seasonality, with peak fertility occurring in the Northern Hemisphere from March to June, corresponding to the spring breeding period when daylight lengthens. This photoperiodism influences reproductive physiology through the pineal gland, which secretes melatonin in response to shorter days during winter, suppressing gonadal activity; as daylight increases, melatonin decreases, stimulating the hypothalamic-pituitary-gonadal axis to enhance libido and semen quality. In feral populations, breeding activity intensifies during this time, aligning with mare estrus patterns to optimize foal survival.^[45]^[46]^[47] Sperm production in stallions is continuous throughout the year, but it peaks during the breeding season, with total motility often reaching 80-85% and progressive motility around 60%, compared to lower values in winter. This elevation supports higher conception rates, particularly as mares typically foal in spring (April-May), entering a fertile "foal heat" 7-12 days postpartum, which prompts immediate rebreeding and synchronizes the next gestation cycle for spring foaling the following year. Environmental factors play a key role; adequate nutrition, including balanced energy and micronutrients like selenium and vitamin E, supports spermatogenesis, while deficiencies can impair sperm quality. Conversely, stress from high temperatures, social isolation, or overexertion reduces libido and testosterone pulsing, leading to diminished sperm production and motility.^[48]^[49]^[50] Stallions generally maintain fertility from sexual maturity around 2-3 years until 15-20 years of age, after which reproductive capacity declines gradually due to age-related reductions in testicular function and hormone levels. Testosterone concentrations, which average 1-3 ng/mL during peak breeding seasons in mature stallions, drop to <1 ng/mL or lower in older individuals, correlating with decreased libido, semen volume, and sperm viability. This decline is exacerbated by cumulative environmental stressors but can vary based on genetics and management in undomesticated settings.^[51]^[52]^[53]

Artificial Breeding Techniques

Artificial breeding techniques for stallions primarily involve semen collection and processing methods to facilitate controlled reproduction in domestic equine management. The most common semen collection technique is the use of an artificial vagina (AV), which simulates the natural mounting process by allowing the stallion to mount a mare in estrus or a padded dummy mount while the penis is directed into the warmed, lubricated AV.^[54] This method typically yields one to three ejaculates per collection session, with the first ejaculate containing the highest sperm concentration (8-10 billion spermatozoa) and subsequent ones providing additional viable doses.^[19] For non-compliant or medically compromised stallions, electroejaculation under general anesthesia serves as an alternative, involving electrical stimulation of the pelvic nerves to induce ejaculation, though it is less preferred due to potential stress and lower semen quality.^[55] Once collected, stallion semen is extended and processed for insemination, categorized as fresh, cooled, or frozen based on storage needs. Fresh semen is used immediately on-site and maintains high viability, while cooled semen, diluted in extenders such as skim milk-egg yolk formulations, remains viable for 24-48 hours when stored at 4-5°C in specialized shipping containers, enabling transport to distant locations.^[56] Frozen semen, preserved using cryoprotectants like 5% glycerol in egg yolk-based extenders, allows long-term storage at -196°C in liquid nitrogen, though it requires careful thawing protocols to preserve motility.^[57] Success rates for artificial insemination (AI) with these types generally range from 50-70% per estrous cycle, with fresh and cooled semen achieving higher pregnancy rates (60-90%) compared to frozen (55-75%), influenced by stallion fertility, mare receptivity, and timing.^[54]^[58] Advanced techniques like embryo transfer (ET) and in vitro fertilization (IVF) incorporate stallion sperm to enhance reproductive efficiency. In ET, oocytes from donor mares are fertilized via AI with fresh, cooled, or frozen stallion semen, and resulting embryos are flushed and transferred to recipient mares, allowing elite broodmares to produce multiple foals annually without pregnancy risks.^[59] IVF utilizes cryopreserved stallion sperm to fertilize in vitro-matured oocytes, with recent protocols demonstrating successful fertilization rates using frozen-thawed semen after shortened pre-incubation periods of about 9 hours.^[60] Cryopreservation protocols for stallion sperm in these applications emphasize glycerol at 5% concentration to mitigate freeze-thaw damage, ensuring sufficient post-thaw motility for advanced breeding.^[57] Artificial breeding techniques, particularly AI, play a key role in genetic selection and breed improvement by enabling access to superior stallion genetics worldwide without physical transport, thereby increasing genetic diversity and reducing transmission of heritable diseases.^[54] This approach has facilitated targeted selection for traits like performance and temperament, with studies indicating potential genetic progress increases of up to 270% in stallions through integrated reproductive technologies.^[61] By minimizing direct contact, AI also lowers risks of venereal disease spread compared to natural breeding.^[62]

Domestication and Management

Handling Domesticated Stallions

Handling domesticated stallions requires careful attention to their natural behaviors and potential for aggression, particularly influenced by hormonal drives and territorial instincts. Early socialization is a key training principle, beginning in foalhood to mitigate aggressive tendencies later in life. By introducing young stallions to a variety of humans, environments, and other horses in controlled settings, handlers can foster trust and reduce fear-based reactions. Studies on equine behavior indicate that stallions handled extensively from birth exhibit lower levels of aggression during routine management compared to those with limited early exposure.^[63]^[64] Desensitization techniques, often conducted in round pens, further support safe handling by gradually exposing stallions to potentially stimulating or frightening stimuli. This method involves using pressure and release principles, where the horse is encouraged to move in a circular pattern until it shows signs of relaxation, rewarding calm responses to build confidence. For stallions, specific desensitization to scents or sights of mares in estrus is crucial to prevent uncontrolled excitement during daily activities; handlers may introduce diluted pheromones or visual cues in the round pen to condition appropriate responses without direct contact. This approach aligns with operant conditioning principles widely used in equine training to promote compliance and reduce stress.^[65]^[66] Restraint methods are employed judiciously during veterinary procedures or grooming to minimize risk of injury from bites or kicks, emphasizing non-confrontational techniques. A lip twitch, consisting of a rope or chain loop tightened around the upper lip, provides distraction and mild pain to encourage stillness without escalating aggression; it should be applied firmly but not excessively to avoid tissue damage. Hobbles, which secure the legs together, are used sparingly to restrict movement, often in combination with sedation for safety. Lip chains or stud chains, run through the halter and over the sensitive gum, offer effective control for leading excitable stallions, particularly in breeding or show settings, by allowing handlers to apply pressure without direct physical confrontation. Always prioritize calm verbal cues and positioning at the horse's side to de-escalate potential threats.^[67]^[68]^[69] Facility design plays a vital role in preventing injuries from inter-stallion conflicts and reducing overall stress. Stallions should be housed in separate paddocks with double fencing to eliminate physical contact between individuals, minimizing fights over dominance or resources. Visual barriers, such as solid panels or dense shrubbery between enclosures, help block lines of sight to mares or rival stallions, thereby lowering arousal levels and cortisol responses associated with chronic stress. Paddocks for stallions typically measure at least 1-2 acres to allow natural movement, with secure, high fencing (at least 5-6 feet) to contain their strength and prevent escapes. These designs comply with welfare standards that prioritize species-appropriate housing to support mental and physical health.^[70]^[71]^[72] Legal and ethical considerations in stallion handling are governed by international equestrian regulations, which emphasize temperament and welfare assessments. The Fédération Equestre Internationale (FEI) mandates horse inspections at competitions, including evaluations of demeanor and responsiveness to ensure stallions pose no undue risk to riders, officials, or other horses; aggressive or unmanageable animals may be disqualified. Handlers must adhere to codes of conduct prohibiting abusive restraints or overworking, with penalties for violations to uphold equine welfare. Nationally, organizations like the American Association of Equine Practitioners reinforce ethical training practices, advocating for positive reinforcement over punitive methods to align with animal rights principles.^[73]

Health Considerations and Veterinary Care

Stallions are particularly susceptible to reproductive health issues due to their active involvement in breeding activities. Orchitis, an inflammation of the testes, can arise from bacterial infections, trauma, or hematogenous spread, leading to swelling, pain, and potential fertility impairment if untreated.^[74]^[75] Treatment typically involves systemic antibiotics for infectious causes, alongside supportive care such as rest and anti-inflammatories to reduce swelling. Breeding injuries, including penile lacerations and abrasions, commonly occur during mounting attempts from kicks by mares or contact with tail hair, resulting in immediate pain, hemorrhage, and risk of secondary infection.^[76]^[77] These injuries often require prompt veterinary intervention, including wound cleaning, suturing if necessary, and antibiotics to prevent complications like fibrosis that could affect future breeding. Routine veterinary exams for breeding stallions include semen analysis to assess sperm motility, concentration, morphology, and volume, providing early detection of subfertility.^[78]^[79] Behavioral factors in stallions can elevate certain health risks, particularly those exacerbated by stress from territoriality or isolation. Among horses presenting with colic, intact males (stallions) had a higher surgical intervention rate (55.8%) compared to geldings (24.5%), according to a 1989 study.^[80] Laminitis, a painful inflammation of the laminae in the hoof, is linked to obesity in stallions, where excess body fat contributes to insulin dysregulation and increased mechanical stress on the feet.^[81]^[82] Preventive veterinary care for stallions emphasizes standardized protocols tailored to their physiology. Core vaccinations, including tetanus toxoid and rabies, are recommended annually for all horses, including stallions, to protect against widespread threats like wound infections from breeding trauma or wildlife exposure.^[83]^[84] Parasite control involves deworming at least twice yearly—typically in spring and fall—using products like ivermectin or moxidectin, with fecal egg counts guiding additional treatments to address high-shedder status, as stallions' robust metabolism may influence parasite burdens.^[85]^[86] Stallions generally share the equine average lifespan of 25-30 years, influenced by genetics, nutrition, and management, though breeding individuals require ongoing monitoring for age-related fertility decline.^[87] Ultrasound examinations of the testes and accessory sex glands are essential for detecting degenerative changes, such as reduced testicular size or echotexture alterations, that signal diminishing spermatogenesis in older stallions.^[88]^[89] These evaluations, combined with semen assessments, help maintain reproductive viability into advanced age.

Geldings and Behavioral Changes

Castration, or gelding, involves the surgical removal of both testes from a stallion to eliminate testosterone production. The procedure is typically performed on horses aged 1 to 2 years under general anesthesia in a recumbent position, though standing laparoscopic methods exist for older animals. Two primary techniques are used: the closed method, where the parietal vaginal tunic remains intact around the testes, and the open method, where the tunic is incised to allow drainage and reduce swelling risk.^[90]^[91] Owners and trainers pursue castration primarily for safety in mixed-sex or multi-horse environments, where intact stallions may exhibit heightened aggression or territorial behaviors toward other horses or handlers. In performance disciplines such as dressage, show jumping, and racing, gelding enhances focus and consistency by minimizing hormonal distractions, with geldings comprising a majority of competitors in international events. Economically, it is favored for non-breeding males, as it simplifies management and reduces the need for secure facilities required for stallions.^[92]^[93]^[94] Post-castration, testosterone levels decline rapidly within 48 hours, but noticeable behavioral shifts, such as reduced libido and aggression, typically emerge within 2 to 4 weeks, with full calming effects potentially taking 4 to 6 months depending on the horse's age and prior experiences. Geldings generally become more tractable for riding and training, exhibiting less mounting or dominance displays compared to intact stallions, though learned behaviors may persist longer in older animals.^[92]^[95]^[96] Physically, the absence of testosterone leads to gradual changes over 6 to 12 months, including decreased muscle bulk, particularly in the neck and shoulders, resulting in a less cresty appearance and softer overall conformation. These alterations do not impair athletic capability but align the horse's physique more closely with that of a mare, without the possibility of reversal.^[96]^[95]

Ridglings and Surgical Complications

A ridgling, also known as a cryptorchid stallion, is defined as a male horse in which one or both testicles fail to descend into the scrotum, remaining instead in the inguinal canal or abdominal cavity, thereby retaining partial testosterone production and stallion-like behaviors. This condition can also arise from incomplete castration, where surgical removal leaves behind ectopic testicular tissue capable of hormone secretion. There are two primary types: inguinal ridglings, where the testicle is retained in the inguinal canal, and abdominal ridglings, where it remains within the peritoneal cavity, with the left testicle more commonly abdominal and the right inguinal.^[97]^[98] Surgical interventions to address ridglings, such as cryptorchidectomy, carry risks of complications including post-operative infections, hemorrhage, and persistent stallion behaviors due to incomplete removal of testicular tissue. Infections, often manifesting as scrotal swelling or purulent discharge, are among the most common issues, with overall post-castration complication rates historically ranging from 10% to 60% but reduced in modern practices. Hemorrhage, typically from the testicular artery, occurs in approximately 1.8% to 2.4% of cases, particularly in older horses, and may require immediate intervention. Retained masculine behaviors affect 20% to 30% of cases involving incomplete castration or ectopic tissue, leading to challenges in management and potential fertility issues.^[99] Diagnosis of ridglings relies on a combination of imaging and hormonal assays to confirm the presence of retained testicular tissue. Transabdominal or inguinal ultrasonography provides high accuracy, detecting 100% of inguinal testicles and 72.7% of abdominal ones, allowing precise localization without invasive procedures. Hormonal tests measure basal serum testosterone levels, which exceed 0.68 ng/mL in cryptorchids compared to 0.15 ng/mL in fully castrated geldings, with stimulation via human chorionic gonadotropin (hCG) prompting an increase to over 1.05 ng/mL within 60 minutes in affected horses. Additional markers like anti-Müllerian hormone (AMH) or conjugated estrogens further distinguish ridglings from geldings.^[97]^[100] Treatment involves secondary surgical removal of the retained testicle(s), ideally performed by a board-certified veterinary surgeon to minimize risks. For abdominal ridglings, laparoscopy offers advantages over traditional laparotomy, including faster recovery (turnout possible after 72 hours versus 10-14 days) and lower complication rates compared to historical open techniques. Modern laparoscopic approaches have notably decreased the incidence of post-surgical issues, enhancing outcomes in breeds prone to this condition.^[97]^[99] Cryptorchidism affects approximately 3-4% of colts overall, with prevalence rising to higher rates in specific breeds such as Quarter Horses, which represent the most commonly impacted group at around 47% of cases in surveyed populations. Other predisposed breeds include American Saddlebreds and Percherons. While congenital incidence remains stable, the modern use of advanced diagnostics and laparoscopic surgery has lowered the rate of surgical complications associated with ridgling treatment compared to historical methods.^[98]^[97]

References

[1]
Stallion - Texas Advanced Computing Center
Stallion's configuration enables the processing of datasets at massive scale, and the interactive visualization of substantial geometries. A large, shared file ...
[2]
None
### Summary of STALLion Visualization System
[3]
New Year, New Stallion - Texas Advanced Computing Center
one of the highest-resolution tiled displays in the world — has been used by researchers to study impactful data such as the earliest ...
[4]
Stallion User Guide - TACC HPC Documentation
Jan 25, 2023 · Stallion is an ideal resource for users wishing to explore and present terascale datasets / geometries or ultra high-resolution imagery.
[5]
Evaluation of the sexual dimorphism in Mangalarga Marchador ...
Stallions were larger than mares for almost all linear measures, except for back-loin length, hip width, and distance from elbow to knee. Shoulder-humerus and ...
[6]
Anatomy, physiology and reproduction in the stallion - Ontario.ca
promotes the development and function of the accessory sex glands, causes development of secondary sex characteristics and is ...
[7]
Sexual dimorphism through androgen signaling - NIH
Jul 27, 2022 · Neck crests are also prominent in male bulls and stallions due to greater muscle build-up in the head, neck, and shoulder regions as compared ...Missing: crested | Show results with:crested
[8]
Thoroughbred Horses | Oklahoma State University
The average height of today's Thoroughbred is a little over 16 hands, as opposed to the 14-hand average height of the horses from which the breed originated.
[9]
Exploring equine breeds: The Arabian - MSU Extension
Jun 26, 2014 · The average height is between 14.1 to 15.1 hands (a hand is 4 inches) ... Kellogg donation of the Arabian stallion Amidore. Later, the ...
[10]
Horses | Small Acreage Landowners
The average horse weighs between 900 - 1,100 lbs, but this can vary by breed. Horses will eat between 1.5 - 2.5% of their weight each day in dry forage.
[11]
[PDF] HORSE JUDGING I - WHAT TO LOOK FOR
SEX AND BREED CHARACTER. By sex character, we mean masculinity in the stallion and femininity in the mare. The stallion should have a bolder, stronger, head ...
[12]
Stable Talk: Horse Terms - Kentucky Equine Research
Jan 17, 2018 · A stallion is a mature male horse at the age of four or older; a mare is a mature female horse at the same age. A gelding is a castrated male horse of any age.
[13]
Equine Reproductive Maturity in Mares and Stallions | EquiMed
Sep 12, 2018 · Although most stallions begin to produce sperm as early as 12 to 14 months, most are at least 15 months or older before they can successfully breed.
[14]
Age-appropriate training: this is when horses physically mature
Jul 3, 2025 · No horse is skeletally mature until around six years of age at the earliest, with some not reaching full skeletal maturity until eight years of age.
[15]
https://yourhorsefarm.com/when-do-horses-stop-growing/
[16]
Testicular growth, hormone concentrations, seminal characteristics ...
Seminal collections were attempted monthly from 48 to 64 weeks and every 2 weeks thereafter until puberty resumed every 3rd day from 96 weeks for 15 ejaculates.
[17]
Cryptorchidism in Horses - PetMD
Jan 24, 2023 · Most stallions will have their testicles completely descended by 4 weeks of age.
[18]
Horse Breeding for Dummies Part 6 - Stallion Basics
Jul 12, 2012 · Sexual maturity is reached at about 4 years of age, but many colts will exhibit stallion-like behavior and sexual activity as early as 8 months ...
[19]
At What Age Does a Stallion's Fertility Peak? - The Horse
Age can affect a stallion's fertility and his ability to settle mares. Reproduction specialist Dr. Ryan Ferris explains in this podcast.
[20]
When Do Horses Stop Growing?
Feb 23, 2021 · A draft horse may still be growing even at eight years old. Quarter Horses and Thoroughbreds tend to become fully grown at five to six years old ...
[21]
Stallion Anatomy Exam | Extension Horses
Jan 31, 2020 · The stallion's penis consists of 3 parts: (1) the root or bulb, (2) ... Stallions older than 7 years of age tend to have greater scrotal widths ...
[22]
Reproductive Tracts and Genitalia – CVM Large Animal Anatomy
Identify and describe the various parts of the male reproductive tract; identify associated structures of the ungulate testis.
[23]
Stallion Reproductive Evaluation
Nov 15, 2022 · Stallion Identification Registration name and number, age, and breed are recorded. Coat color and markings, lip tattoos, microchip information ...Missing: distinctions | Show results with:distinctions
[24]
Breeding Soundness Examination of Stallions
A stallion is considered satisfactory if it produces at least 1 billion progressively motile and morphologically normal sperm in the second (or third) ejaculate ...Missing: sources | Show results with:sources
[25]
https://aaep.org/resource/position-on-the-use-of-anabolic-steroids/
[26]
[PDF] For steroid hormone (testosterone, DHP, progesterone, es
Equine Males: Cryptorchidism (not recommended, serum AMH and testosterone levels suggested). Gelding <0.1 ng/mL; Cryptorchid 35-60 ng/mL; Stallion 140 – 200 ng/ ...
[27]
Physiology and Endocrinology of Stallions | Veterian Key
Sep 3, 2016 · Increasing GnRH levels stimulate increased LH and FSH production by the pituitary and corresponding increases in testosterone, estradiol, and ...Missing: sources | Show results with:sources
[28]
Luteinizing hormone concentrations in healthy horses and ... - NIH
17, 23, 24 In 1 study, stallions during summer had a mean LH concentration of 0.52 ± 0.13 ng/mL, which decreased to 0.25 ± 0.08 ng/mL in the winter. 11 Removal ...Missing: sources | Show results with:sources
[29]
Muscle characteristics in Thoroughbreds of different ages and sexes
The percentage of Type IIA fibres varied with age and sex, increasing in stallions from 34 to 53 per cent and in mares from 27 to 45 per cent, respectively.Missing: fiber | Show results with:fiber
[30]
Position on the Use of Anabolic Steroids – AAEP
In horses, anabolic steroids may stimulate appetite and increase muscle mass, particularly when there has been marked tissue breakdown associated with disease, ...
[31]
Pelvic Limb – CVM Large Animal Anatomy
Females of different species (e.g., mare, cow) tend to have larger diameter pelvic inlets than males.<|separator|>
[32]
Experimental investigation of bone mineral density in ... - NIH
Sep 30, 2015 · To investigate changes in BMD with age, 37 right metacarpal bones, including 7 from horses euthanized because of fracture were examined by QCT.Missing: 1.2-1.5 cm²
[33]
A Quick Look at the Amazing Equine Heart - The Horse
Heart Size The average horse's heart weighs approximately 1% of its body weight, so a standard 1,000-pound horse has a heart weighing a whopping 10 pounds. The ...Missing: percentage | Show results with:percentage
[34]
Horse Lungs vs. Human Lungs | Learn About Horse Lung Health
### Lung Capacity and Tidal Volume in Horses
[35]
Do horses really have thick skin?
May 27, 2017 · The horse's collagen layer was roughly 1mm thicker than the human's. This isn't very much though and has little bearing on pain sensitivity!Missing: stallions | Show results with:stallions
[36]
Ultrasonographic Assessment of Regional Fat Distribution and Its ...
This study expands our knowledge about the distribution of regional fat deposition. The influence of gender and age on body condition score (BCS) and ...
[37]
Social organisation in herds of horses
### Summary of Herd Social Organization (Stallions)
[38]
Social Behavior of Horses - Merck Veterinary Manual
The highest-ranking stallion in a band does most of the breeding, because he is the first to secure access to a receptive female and the first to displace a ...
[39]
The Social and Reproductive Challenges Faced by Free-Roaming ...
The young, dispersed colts often form a single-sex group, called a “bachelor band”. Older stallions who have lost their mares can also join bachelors [23].
[40]
[PDF] Wild Horse Behavior - National Park Service
Aggressive behaviors. Remember that these aggressive behaviors can be directed toward other animals, like dogs, and toward people. Keep your dog on a leash ...
[41]
How to Handle 8 Stallion Behavior Problems - AQHA
Dec 15, 2020 · How to handle it: Avoid trying to tug the horse down with the lead. “Rearing is actually an inter-male aggressive behavior in horses,” Dr.Nipping And Biting The... · Kicking During Prep · RearingMissing: displays lowered
[42]
Basics of Equine Behavior | Extension Horses
Jul 31, 2019 · Snapping: This is seen in foals showing submission to an older horse. · Jaws open with teeth exposed: this shows aggression or possible attack.
[43]
Przewalski's Horse - San Diego Zoo Animals & Plants
To protect their little ones, mares form a defensive circle around their young, and the stallion trots around the circle and charges. At night, one or more ...
[44]
Stallion Reproductive Behavior - Veterian Key
Jun 4, 2016 · Stallion display a characteristic precopulatory sequence beginning with nose-to-nose contact associated with a characteristic soft nicker ...
[45]
Stallion Scent-Marking Behavior: Przewalski Horse Function
Nov 29, 2006 · Thus, the most likely function of scent marking in stallions is a form of female resource defence, although the role of marking stud piles and ...
[46]
Horse Behaviors - Cape Lookout National Seashore
Dec 21, 2017 · These stallions are in charge and spend a lot of time and energy guarding their harem. If another stallion comes too close or attempts to steal ...Missing: nips post- copulation
[47]
Herding and snaking by the harem stallion in domestic herds
Herding behaviors were compared among four successive treatments (six mares alone, stallion added, two new mares added, and entire herd moved to a new pasture).Missing: guarding nips post- copulation
[48]
[PDF] Wild Horses and Burros Management Handbook
Jul 7, 2010 · ... foal mortality. Research shows that at 15-33 percent of foals are sired by non-harem stallions, making it unlikely that fertility control ...
[49]
Using Science to Improve the BLM Wild Horse and Burro Program: A ...
Dominant stallions did not sire about one-third of the foals born in intact harem bands. There was no evidence of loss of herterozygosity in the populations ...
[50]
Aspects of Breeding Stallion Management with Specific Focus on ...
This manuscript aims to review the effects of housing and management on behavior, welfare and fertility of breeding stallions.
[51]
Reproductive Endocrinology of the Stallion | Veterian Key
Jun 8, 2016 · Testosterone levels prior to puberty remained low and did not increase at 40 weeks in conjunction with the LH or FSH rise but then rapidly ...Hpt Axis · Prolactin, Thyroid Hormone... · Endocrine Factor
[52]
Regulation of seasonal reproductive activity in the stallion, ram and ...
The pineal hormone melatonin is the common link between photoperiod and reproduction. An increase in the daily diurnal period of melatonin secretion is ...Missing: quality | Show results with:quality
[53]
Seasonal variations in quantitative and qualitative sperm ... - NIH
May 14, 2020 · Horses are seasonal breeders with a natural breeding season beginning in spring and extending through midsummer.
[54]
The dating game - Older stallions require thorough evaluations to ...
Nov 1, 2004 · Older stallions should be neither too heavy nor too thin as both extremes will reduce fertility. Many supplements are available claiming to ...
[55]
The Reproductive Cycle of Horses - Management and Nutrition
The cervix and uterus have minimal tone. Mares have 3 or 4 prolonged intervals of estrus (periods of sexual receptivity to the stallion) during the vernal ...
[56]
Strategic approaches to improve equine breeding and stud farm ...
Mares raised in the northern hemisphere have a reproductive season that consists of anestrus in the winter, a spring transition (about mid-February to mid- ...
[57]
Effect of age, pubertal stage and season on testosterone ... - NIH
In breeding season, the plasma testosterone concentration significantly increased to reach its maximum at 10 years of age (6.3 ng/ml), then decreased sharply ...
[58]
Evaluation of the sexual behavior and testosterone concentrations of ...
Usually, the stallion achieves an erection and is able to mount, but is not able to ejaculate. The aim of this study was to evaluate the sexual behavior and ...
[59]
Artificial Insemination in Horses - PetMD
Mar 24, 2023 · The collection of semen from stallions is typically done using an artificial vagina (AV), which mimics the natural reproductive process. The ...
[60]
A comparison of electroejaculation and epididymal sperm collection ...
Electroejaculation under general anesthesia would simplify semen collection from stallions with acute irreparable conditions. Successful epididymal sperm ...
[61]
Planning to breed with cooled semen
Cooled semen is only viable for 48 hours after collection. Thus, you must closely monitor your mare and understand the stallions shipping schedule.
[62]
Freezing of equine semen is influenced by exposure time ... - PubMed
Results: Considering the total and progressive motility of the spermatozoa, we concluded that protocols using 5% glycerol for 15 and 30 min exposure, 4% ...
[63]
Frozen Equine Semen Basics
The conception rate for frozen semen ranges from 55 to 75% or better. If the conception rate of the person you are interviewing falls well below that, ...
[64]
Embryo Transfer in Horses - Management and Nutrition
Frozen semen from deceased stallions can be efficiently used to produce in vitro embryos by using only a portion of a frozen semen straw to provide sperm ...
[65]
Equine in vitro fertilization with frozen-thawed semen is associated ...
May 13, 2025 · We conclude that frozen-thawed equine sperm can successfully fertilize oocytes after a shortened pre-incubation time of 9 h.
[66]
Contribution of Reproduction Management and Technologies to ...
The calculation showed that using all ways of improvement could provide an increase in genetic progress of up to +270% and +226% in mares and stallions, ...
[67]
https://ouv.vt.edu/content/dam/ouv_vt_edu/sops/large-animal/sop-equine-restraint.pdf
[68]
Keeping Stallions in Groups—Species-Appropriate or Relevant to ...
May 4, 2021 · ... socialization of active breeding stallions outside the ... Examining the possible mechanisms of multi-stallion groups in horse societies.
[69]
Behavioral Considerations When Housing Horses - MSU Extension
Apr 2, 2012 · Socialization can be ... A double fence line is often used with a stallion paddock to ensure that a stallion cannot reach other horses.
[70]
Training Horses Safely | Oklahoma State University
The “stimulus, response, and reinforcement” principle is used to train horses. We apply a cue (stimulus), the horse reacts (response), and we reinforce the ...
[71]
Neigh-bours: Why every young horse needs good friends. A pilot ...
This study aimed to evaluate how the maintenance of social contacts impacts the behaviour of young horses during breaking-in.Missing: techniques | Show results with:techniques
[72]
[PDF] SOP: Equine Restraint Techniques - Virginia Tech
Dec 12, 2017 · Grab upper lip firmly in a similar fashion to the neck twitch hold; again, working the twitch may assist with distraction and/or sedative effect ...
[73]
[PDF] Equine Physical Examination and Restraint Review
Young racehorses and stallions are frequently led using a chain over the nose. ii. Lip chain. Very commonly used in Thoroughbreds. The instructor will.
[74]
Behavior – Veterinary Preventive Medicine
Lip cords or chains – A cord (shoe-lace often is used) or chain is run across the inside of the lip. This prevents the horse from backing up or rearing.
[75]
[PDF] Code of practice for the welfare of horses, ponies, donkeys and their ...
Stallions may require a double fence line and possibly an electric fence line along the top of the paddock rail. This is to prevent aggression between ...<|control11|><|separator|>
[76]
Welcome Neigh-bor! The New Horse Arrival Guide
Mar 21, 2018 · Rearing up, pacing back and forth, kicking, or jumping fences are possible behaviors to look out for. It is possible that some stallions may be ...
[77]
[PDF] husbandry standards for keeping wild equids in captivity, 2001
groups comprised of a single stallion and multiple mares and foals (typically 1 stallion ... 1.4.9.2 Solid visual barriers (6-8' high) are best utilized ...
[78]
FEI Rules & Regulations
All the FEI's Rules & Regulations are available in our special FEI Rules hub, where they are arranged by theme and can be viewed online or downloaded.
[79]
Case Report - Orchitis, epididymitis and pampiniform phlebitis in a ...
Orchitis can be caused by trauma, infection, autoimmune disease or parasites. Epididymitis is usually of infectious cause in horses, and reported ...
[80]
Diagnostic Approach to Equine Testicular Disorders - MDPI
4.4. Orchitis and epididymitis are rare in stallions [16,98,99]. Orchitis can be caused by infections extending from a scrotal wound, hematogenous spread, ...
[81]
Penis: trauma in Horses (Equis) | Vetlexicon
Abrasions and lacerations of the penis are relatively common in stallions. Cause: often occurs during mating. Signs: wounds usually superficial; ...
[82]
Reproductive Emergencies in the Stallion - ScienceDirect.com
Direct trauma to the penis generally occurs during breeding attempts when the penis is fully erect. Instances include kicks from a mare; tail hair abrasions; ...
[83]
Semen Evaluation | Veterian Key
Oct 30, 2022 · Semen evaluation includes measuring volume, observing color, determining sperm concentration, and assessing sperm motility to assess stallion ...
[84]
Approaches to Breeding Soundness Examination and Interpretation ...
Both routine and more in-depth tests are available to assess sperm quality. Test selection must fit within the time/economic constraints of the stallion owner.Review Article · Semen Analysis · References (32)
[85]
Association of age, sex and breed factors in acute equine colic
Intact male horses had a higher overall surgical rate (55.8%) than geldings (24.5%) or females (30.9%). Older horses tended to have a lower overall surgical ...
[86]
Obesity and obesity-associated metabolic disease conditions in ...
Nov 20, 2023 · Background: Equine obesity combined with insulin dysregulation (ID) is a major risk factor associated with laminitis.
[87]
Perils of Pudge: Obesity and Laminitis in Horses - Kentucky Equine ...
Mar 26, 2018 · “Overweight and obese horses are at risk for developing insulin resistance, metabolic syndrome, and life-threatening laminitis.” In a separate ...
[88]
Adult Horse Vaccination Chart – AAEP
Core vaccinations protect against diseases that are endemic to a region, are virulent/highly contagious, pose a risk of severe disease.
[89]
Vaccination | Equine Disease Communication Center
The 5 core vaccines for horses are tetanus, Eastern EEE and Western Equine Encephalomyelitis WEE), West Nile Virus (WNV) and rabies.Missing: stallions | Show results with:stallions
[90]
https://open.lib.umn.edu/largeanimalsurgery/chapter/equine-castration-overview/
[91]
Decoding Dewormers: Types, Resistance Concerns, and Use for ...
May 2, 2025 · Recommended Deworming Frequency for Adult Horses ... The AAEP recommends that all adult horses be treated with a dewormer at least one to two ...<|control11|><|separator|>
[92]
How Long Do Horses Live - WebMD
Jul 18, 2025 · Lifespan of Horses. The average horse lives for 25 to 30 years. However, in rare cases, domestic horses have lived into their 50s or 60s.Missing: stallion | Show results with:stallion
[93]
Diagnostic Methods for Evaluation of Stallion Subfertility: A Review
Ultrasound imaging has provided much-improved diagnostic methods for evaluation of the external and internal genitalia of the stallion.
[94]
Advances in the ultrasound diagnosis in equine reproductive medicine
In the stallion, colour Doppler ultrasound has improved the diagnostic potential of B‐mode ultrasound, improving the differential diagnosis of pathologies such ...
[95]
Equine Castration Overview – Large Animal Surgery
Castration may be performed via an open or closed method, depending on whether the vaginal tunic is cut to expose the testicle (open) or removed with the ...
[96]
Equine Castration - American College of Veterinary Surgeons
While most horses experience positive changes following castration, learned stallion behaviors often take a period of time and training to change, and could ...<|control11|><|separator|>
[97]
Castration in Horses - PetMD
Dec 14, 2022 · Behavioral Changes After Castration. In time, your horse will have less “studly” urges, unless your horse was very mature and had been used for ...
[98]
The Age and Gender Profile of Showjumping Horses - Hippomundo
Jul 15, 2025 · When we look at the entire sport population across all levels, we see a much more balanced distribution. Of the 56,998 sport horses, 57% are ...
[99]
https://beva.onlinelibrary.wiley.com/doi/10.1111/eve.13880
[100]
[PDF] Gelding and Aftercare
Depending at what age he was gelded, the horse may need as long as 4-6 months to mentally and physically forget he was a stallion. After castration, the ...
[101]
https://paulickreport.com/news/geldings-does-the-ultimate-equipment-change-actually-impact-performance/
[102]
Cryptorchidism (Undescended Testicles) in Horses
Cryptorchidism, meaning 'hidden testes,' is when one or both testicles do not descend into the scrotum, and may be located in the abdomen or inguinal canal.
[103]
Cryptorchidism in Horses
Jan 11, 2022 · For these tests to be accurate, the horse must be at least 12 months of age. Veterinarians might run testosterone tests in conjunction with ...
[104]
A review of prevention and management of castration complications
Aug 23, 2023 · This article will briefly review strategies to prevent complications and surgical castration techniques before reviewing, in-depth, the following complications.
[105]
Clinical, Hormonal and Ultrasonograph Approaches to Diagnosing ...
The highest levels of testosterone were found in stallions' blood (2.3 ng/ml), they were lower in cryptorchids (0.68 ng/ml) and lowest in geldings (0.15 ng/ml).Missing: treatment ridglings