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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Includes slow or variably inadequate precopulatory behaviors, sexual arousal, erection, or copulatory behavior
  • Particular preferences and aversions for mares, handlers, breeding locations, procedures, or equipment have also been demonstrated; can also be general or specific to certain conditions
  • In stallions, can be chronic or intermittent and can include certain aberrant precopulatory or copulatory behaviors—excessive biting or licking, savaging the mare or handler, or premature dismount

Pathophysiology!!navigator!!

In stallions, can be the result of single or multiple factors—genetic predisposition, inadequate social maturation, simple inexperience, suboptimal breeding stimuli, or aversive experience associated with sexual behavior, breeding, or general handling.

Systems Affected!!navigator!!

  • Behavior—other behavior problems, including aggression stereotypies, can follow unresolved or ill-handled sexual behavior dysfunction; it is not uncommon for managers to physically abuse stallions for failure to perform sexually
  • Reproduction—subfertility or infertility

Signalment!!navigator!!

Novice and experienced breeders of any age, breed, or performance type.

Signs!!navigator!!

Historical Findings

  • Current and past general health, attitude, and temperament? Early socialization experience?
  • Training and performance history?
  • What is the stallion fed, including supplements?
  • Any current medications?
  • Current work and performance schedule?
  • How is the stallion housed?
  • Breeding experience?
  • Age of first use?
  • Libido and temperament?
  • General behavior in stall and at pasture?
  • Step-by-step details of behavior in sexual situation?
  • Past and current breeding schedules and results?
  • Natural cover or collection of semen?
  • Stimulus and mount mares used?
  • How is the stallion handled for breeding?
  • Experience of personnel?
  • Behavior of any other stallions at same facility?

Physical Examination Findings

Usually normal, but may yield evidence of current or possible past sources of discomfort (e.g. stallion ring, other scars).

Causes!!navigator!!

  • Inexperience
  • Pain associated with breeding—legs, feet, chest, shoulder, stifle, back, penis, testicles, cord torsion, or inguinal testicle
  • Punishment associated with sexual behavior
  • Antimasturbatory devices or practices
  • Injudicious punishment or rough or inconsistent handling during breeding, particularly intolerance of normal sexual behavior or overhandling of the head
  • Breeding accidents—slipping during breeding, hitting the head on a low ceiling when mounting, or being kicked by a mare
  • Overuse as a breeding stallion or overwork in performance
  • Abuse
  • Suboptimal stimulus mare
  • Innate mare preferences
  • Suboptimal breeding environment—poor footing, low ceilings, or noise and distractions
  • Suboptimal artificial vagina or dummy mount conditions or techniques
  • Too rigid or too flexible breeding organization

Risk Factors!!navigator!!

  • Age <2 years
  • Novice breeders >5 years
  • Sire with low or temperamental libido
  • Heavy training or work
  • Exposure to anabolic steroids and other performance-enhancing medications and feed supplements
  • Discipline for showing normal sexual behavior
  • Heavy breeding schedule
  • Poor general health
  • Physical abuse
  • Hand-rearing, particularly if isolated from other horses during development
  • Housing conditions—deliberate or inadvertent sensory, exercise, and social deprivation
  • Injudicious, rough, or inconsistent handling during breeding
  • Any musculoskeletal or genital pain, discomfort, or instability
  • Fear of people or a particular person
  • Obesity
  • Severely underweight
  • Extreme hot or cold environmental temperatures
  • Change in environment, housing conditions, or management, which can suppress sexual response
  • Self-serve dummy mounts

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Medical differentials must be ruled out before a primary psychogenic diagnosis can be established.

CBC/Biochemistry/Urinalysis!!navigator!!

Should be normal.

Other Laboratory Tests!!navigator!!

  • Endocrinology—stallion panel (i.e. testosterone, estradiol, luteinizing hormone, follicle-stimulating hormone, triiodothyronine, thyroxine, insulin, and cortisol) should be normal. For old stallions or those with suspected testicular degeneration, human chorionic gonadotropin and GnRH challenge tests may be useful. Use challenge and sampling protocols of an equine endocrine laboratory with a large stallion database and knowledge regarding interpretation of their protocol results
  • Semen—can be evaluated for signs of infection or hemospermia that might suggest urogenital lesions causing discomfort

Imaging!!navigator!!

To rule out sources of present or past musculoskeletal or urogenital pain.

Other Diagnostic Procedures!!navigator!!

  • Cardiovascular examination to rule out aortic iliac disease that may affect breeding ability
  • Musculoskeletal and neurologic examinations on the ground and during breeding
  • Video surveillance in the stall to observe erection and penile movement during normal, spontaneous erections
  • Video surveillance of the stallion in the stall next to a mare or turned out at liberty with or near a mare to determine stallion-like behavior under less controlled conditions
  • Video or direct observation of breeding procedures and stallion handling

Treatment ⬆ ⬇

TREATMENT

Management and Environment

  • To the extent possible, correct obvious housing, handling, and breeding environment deficiencies, providing optimal stimulus mares, and physical facilities for breeding—excellent footing, ample head room, and plenty of space
  • Establish a feeding and exercise program to maximize fitness for breeding and to minimize fatigue and pain
  • Establish a breeding schedule to maximize libido and breeding performance; for stallions with low or variable libido, a breeding schedule of 2 or 3 times weekly usually maximizes arousal and performance
  • To the extent possible, identify and abide any specific preferences or aversions of the animal

Behavior Modification

  • Provide as much uncontrolled access to mares as possible; this likely will increase endogenous male hormones and build confidence in responding to mares
  • For slow-starting, novice breeders, continue daily exposure to breeding, with patient and gentle handling and a variety of stimulus mares; pasture breeding opportunities can build confidence and naturally train a stallion to breed
  • When people are present, they can encourage and positively reinforce sexual arousal and response
  • Educate handlers to use positive reinforcement-based stallion-handling procedures to encourage spontaneous erection and masturbation

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Analgesics or other therapies for management of any potential sources of physical discomfort or instability during breeding
  • Anxiolytics as a training aid to overcome past, negative breeding experiences—diazepam (0.05 mg/kg (to maximum of 20 mg) slow IV 5–7 min before breeding; extralabel use)
  • Unless androgen levels are greater than the normal range, administer GnRH (50 μg SC 2 h and again 1 h before breeding; extralabel use) to boost endogenous androgens, which often increases sexual interest and arousal and appears to make genital tissues more sensitive to stimulation
  • If quick results are needed, short-term treatment with aqueous testosterone (50–80 mg SC every other day for at least 1 week; extralabel use) can effectively increase circulating testosterone and boost libido; the greatest improvement in libido typically occurs after 4–7 days of treatment
  • Imipramine hydrochloride (500–800 mg for each 450 kg (1000 lb) PO 2–3 h before breeding; extralabel use) to lower the ejaculatory threshold and reduce the amount of work needed to breed
  • Drug-induced ejaculation regimens (extralabel use) are available as substitutes for in copula breeding or collection of semen

Precautions!!navigator!!

  • Caution handlers that benzodiazepine anxiolytics can lower the threshold of aggressive as well as sexual behaviors
  • Increasing male hormone levels with GnRH or androgens also likely increases aggressive behavior. If the aggression is not skillfully directed or abided, mare or handler interaction with the stallion can be counterproductive
  • Increasing the dose of testosterone often is tempting, but possible adverse side effects on pituitary gonadal function are a concern
  • At certain levels, imipramine hydrochloride can inhibit rather than enhance ejaculation, disturb bladder neck function, and cause premature flaring of the glans penis. Should these occur, a lower dose usually is more effective at enhancing ejaculation without these side effects

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Once- to twice-weekly follow-up for at least 1 month, with monthly follow-up thereafter during the current breeding season to monitor and fine-tune improvements and medications
  • Reexamination near the end of the current breeding season and near the beginning of the next breeding season, or with change in environment or health status

Possible Complications!!navigator!!

  • Best results occur if everyone involved with the care and handling of the horse communicates openly among each other and with the clinician toward a positive outcome for the stallion
  • Counterproductive blaming or failure of all to cooperate or comply with the treatment plan

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Some stallions become “sour” if continually failing at breeding and may develop self-mutilation or tendencies to savage the mare or handlers
  • Many stallions with low libido actually began as high-energy, unruly stallions that, in association with discipline, became uninterested or slow to respond
  • Subclinical lameness, neurologic disease, or aortic iliac disease that may specifically disturb pelvic circulation or cause hindlimb pain or weakness during copulation

Age-Related Factors!!navigator!!

  • Inadequate sexual interest and response in young novice stallions is more likely to be psychogenic than a physiologic problem
  • Most healthy, sound stallions maintain stable libido through their mature years and into old age. However, with advancing age and accumulated minor physical deterioration, once tolerable musculoskeletal discomfort or disabilities may become more problematic for breeding stallions
  • Cardiac pathology, particularly with advancing age, often is associated with reduced libido, apparent anxiety on exertion during breeding, and delayed or urgent dismount

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

  • Libido problem
  • Erection dysfunction
  • Breeding dysfunction
  • Sexual behavior dysfunction
  • Poor breeding performance

Abbreviations!!navigator!!

GnRH = gonadotropin-releasing hormone

Suggested Reading ⬆ ⬇

McDonnell SM. Sexual behavior dysfunction of stallions. In: Robinson NE, ed. Current Therapy in Equine Medicine, 3e. Philadelphia, PA: WB Saunders, 1992:633–637.

McGreevy P. Equine Behaviour: A Guide for Veterinarians and Equine Scientists, 2e. Philadelphia, PA: WB Saunders, 2012:248–252.

Mills DS, McDonnell S. Domestic Horse: The Origins, Development, and Management of its Behaviour. New York, NY: Cambridge University Press, 2005.

Author(s) ⬆

Author: Sue M. McDonnell

Consulting Editor: Victoria L. Voith