1
Q
[Hormones] GnRH role in stallion reproduction
A
GnRH (from hypothalamus) acts on the pituitary to increase FSH and LH secretion.
2
Q
[Hormones] FSH target and function in stallion
A
FSH acts on Sertoli cells in the testis; stimulates sperm production in response to testosterone.
3
Q
[Hormones] Sertoli cell product
A
AMH: a marker of active testicular tissue.
4
Q
[Hormones] LH target and function in stallion
A
LH acts on Leydig cells in the testicular interstitium; stimulates testosterone production and is necessary to complete spermatogenesis. Also stimulates estrogen production.
5
Q
[Puberty] testicular descent timing
A
Testicular descent occurs between 30 days before birth and 10 days after birth.
6
Q
[Puberty] Onset of increasing LH and FSH in colts
A
LH and FSH begin to increase around 9 months of age.
7
Q
[Puberty] Testicular growth timing
A
Rapid growth and development of testes occur around 12 months of age.
8
Q
[Puberty] Earliest age spermatozoa can be seen in colts
A
Spermatozoa may be seen as early as 14 months (but usually later).
9
Q
[Puberty]time of Testosterone rise and link to puberty
A
Testosterone increases around 20 months; this rise promotes puberty.
10
Q
[Puberty] Definition of stallion puberty
A
Puberty = consistent production of spermatozoa and ability to produce a pregnancy if allowed to breed.
11
Q
[Puberty] Minimal ejaculate parameters for puberty definition
A
Ejaculate of ~50 million sperm with >10% progressive motility.
12
Q
[Seasonality] Are stallions seasonal?
A
Yes – stallions are seasonal breeders but DO produce spermatozoa year-round.
13
Q
[Seasonality] Key factor governing stallion seasonality
A
governed largely by photoperiod (day length) via neuroendocrine pathways (e.g., GnRH and melatonin interactions).
14
Q
[Seasonality] Out-of-season testicular and cellular changes
A
Out of season: testes are ~25% lighter, with 35% fewer Leydig cells and 31% fewer Sertoli cells.
15
Q
[Seasonality] Out-of-season sperm and hormone output
A
Out of season stallions produce ~40–50% fewer sperm; blood hormone concentrations are also lower.
16
Q
Why perform a Stallion BSE?
A
Because stallion work is big money, and horses are often selected for athletic rather than production traits. BSE helps estimate fertility, manage risk, and “clean out” before breeding season.
17
Q
Typical “successful” stallion fertility numbers
A
Target ~90% seasonal pregnancy rate and ~80% foaling rate (though such data may not be available early in a stallion’s career).
18
Q
Major components of a stallion reproductive/BSE exam
A
1) Identification with photos. 2) History (general + breeding). 3) General health exam. 4) External genital exam. 5) Internal genital exam. 6) Semen collection and evaluation. 7) Testing of semen extenders.
19
Q
[BSE – identification] Why detailed identification matters
A
Accurate, photo-based identification ensures BSE results cannot be misapplied to the wrong horse.
20
Q
[Breeding history] Key breeding history questions
A
Conception and foaling rates, methods of breeding (live cover, AI, cooled, frozen), and semen longevity with cooled/frozen use.
21
Q
[General health exam] Neurologic/mobility issues in stallions
A
Assess for blindness, lameness, or ataxia – these may affect ability to safely mount or be managed for breeding.
22
Q
[External genital exam] Testes – key palpation questions
A
Are testes of normal dimension and consistency (impressionable, rubber-like)? Are both fully descended, epidid in right direction, spermatic cord is cranial dorsal
23
Q
[External genital exam] Total scrotal width – how to measure
A
Measure scrotum at its widest point three times and average the values.
24
Q
[External genital exam] Minimum total scrotal width for light horses
A
At least 8 cm in light horse stallions (varies with age).
25
[External genital exam] Relationship between scrotal width and sperm output
Total scrotal width is highly correlated with daily sperm output (DSO).
26
[External genital exam] Testicular volume formula
Testicular Volume (TV) ≈ 0.5233 × Length × Width × Height for each testis.
27
[External genital exam] True DSO determination method
Collect semen daily for 5–7 days (“clean out”) and use later ejaculates to approximate true DSO.
28
[Internal genital exam] Main internal reproductive structures
Includes epididymis, deferent duct/ampullae, vesicular glands, prostate gland, and bulbourethral glands.
29
[Anatomy] Epididymis functions
Transports sperm to the deferent duct, concentrates them, promotes maturation, and stores sperm.
30
[Anatomy] Ampullae description and function
Widened terminal portion of the deferent duct surrounded by smooth muscle that contracts to push sperm into the urethra.
31
[Anatomy] Accessory sex glands in stallion
Vesicular glands, prostate gland, and bulbourethral glands – add gel and fluid to semen.
32
[Microbiology] When to collect pre-breeding culture samples
Collect samples once the stallion is aroused and prior to washing the penis.
33
[Microbiology] Typical culture sites on stallion genitalia
Urethral fossa, urethra, penile shaft, prepuce, and post-ejaculate urethral swab/semen (for proximal tract assessment).
34
[Microbiology] Major bacteria of concern in stallion genital cultures
Pseudomonas aeruginosa and Klebsiella pneumoniae.
35
[Microbiology] Taylorella equigenitalis culture requirements
Taylorella equigenitalis (CEM agent) requires specific sampling and culture on charcoal-based media.
36
[Semen collection] Reasons to observe semen collection
To assess libido, physical ability, readiness, shyness, poor mounting behavior, and overall handling safety.
37
[Semen collection] Physical ability clues from mounting behavior
Stallions with weaker hind limbs may prefer a higher phantom; mounting difficulties can be observed during collection.
38
[Semen collection] Collection methods – phantom vs mare vs artificial vagina
Use a phantom (with or without a teaser mare) or a live mare (may need twitch or hobbles; ovariectomized or in heat). Tail should be wrapped in live-mare breeding.
39
[Semen collection] Key AV conditions for ejaculation
Appropriate combination of temperature and pressure is required; do not over-heat or under-heat the AV.
40
[Chemical ejaculation] Indications for chemical ejaculation
Used for stallions not safe enough to mount, with weak hind limbs, or when physical mounting is not possible.
41
[Chemical ejaculation] Imipramine protocol for chemical ejaculation
Imipramine 0.75–2.0 mg/kg PO given 1–2 hours before attempting collection.
42
[Chemical ejaculation] Xylazine protocol for chemical ejaculation
After teasing, administer xylazine 0.3 mg/kg IV; ejaculation usually occurs within 3–15 minutes while standing without mounting.
43
[Semen evaluation] Gross appearance – normal color and meaning
Normal semen is translucent to milky; increased opacity correlates with higher concentration.
44
[Semen evaluation] Abnormal semen colors and causes
Red (hemospermia), turbid/opaque with pus (pyospermia), yellow (urospermia).
45
[Semen evaluation] Ejaculate volume significance
Ejaculate volume plus concentration help estimate daily sperm output, which correlates with testicular volume.
46
[Semen evaluation] Normal sperm concentration range in stallion
Approximately 100 × 10^6 to 600 × 10^6 sperm/mL.
47
[Semen evaluation] Methods to determine sperm concentration
Densimeter, nucleocounter, or hemocytometer.
48
[Semen evaluation] Main parameters
gross appearance, volume, concetration, morphology, motility, longevity, contamination
49
[Semen evaluation] Motility assessment conditions
Assess motility on a 37°C heated stage at ~1000× magnification using extended/diluted semen.
50
[Semen evaluation] Total vs progressive vs non-progressive motility
Total motility = % moving; progressively motile = forward-moving; non-progressive = moving but not forward (e.g., circular).
51
[Semen evaluation] Minimum progressive motility threshold
>60% progressively motile sperm is considered normal.
52
[Semen evaluation] Effect of temperature on motility patterns
Cold sperm will move in circles and not show true progressive motility; samples must be warmed before evaluation.
53
[Extenders] Purpose of testing semen extenders
Test each new stallion with several extenders to determine which best maintains motility and morphology at 24–48 hours.
54
[Semen dose] Basic dose requirements for cooled semen dose
A dose should contain: 1 billion progressively motile sperm, final concentration 25–50 million/mL, and total volume <60 mL.
55
[Semen dose] Formula approach to calculate raw semen volume
Take what you WANT (1,000 million PMS) ÷ what you HAVE (PMS as a decimal) = mL of raw semen needed.
56
[Semen dose] Centrifugation decision based on raw volume
If calculated raw semen needed is >10 mL, centrifugation of the ejaculate is required to concentrate sperm before extending.
57
[Frozen semen] Basic steps in freezing stallion semen
1) Collect and evaluate semen. 2) Extend ~1:1 and centrifuge with an inert cushion to remove excess fluid. 3) Recover pellet and re-extend with cryoprotectant extenders. 4) Load into straws and freeze using controlled liquid-nitrogen curves. 5) Thaw and re-evaluate motility.
58
[BSE interpretation] Re-exam interval after disease or stress
If a stallion has questionable semen due to illness or stress, re-examine about 70 days later (to allow for a full spermatogenic cycle and transport).
59
[BSE interpretation] Length of spermatogenic cycle in stallion
Approximately 57 days for spermatogenesis plus transport time.
60
[Inguinal hernia] Definition of inguinal/scrotal hernia in stallion
Portion of intestine passes through the vaginal ring into the inguinal canal or scrotum.
61
[Inguinal hernia] Typical presentation in foals
In foals, often congenital and hereditary; may be unilateral or bilateral (left side overrepresented), generally non-painful with easily reducible herniated intestine.
62
[Inguinal hernia] Natural course of foal inguinal hernias
Many resolve spontaneously by ~6 months of age; may be managed with daily reduction and supportive bandage/diaper (“truss”).
63
[Inguinal hernia] Management options for foal inguinal hernia
Manual reduction; truss bandaging; surgery if persistent, large, or complicated.
64
[Inguinal hernia] Adult stallion inguinal hernia significance
In adults, inguinal hernia can cause strangulating intestinal obstruction and colic; requires surgical correction, often with removal of the testicle on the affected side.
65
[Cryptorchidism] Definition in stallions
One or both testes fail to fully descend into the scrotum; terms include “rig,” “rigling,” or “original.”
66
[Cryptorchidism] Normal timing of testicular descent
Testes form near kidneys, pass through inguinal canal at 9–10 months gestation, and descend into scrotum 30 days before to 10 days after birth.
67
[Cryptorchidism] Effect of retention on sperm and hormone production
Retained testes are too warm for sperm production (no spermatogenesis), but testosterone production continues, often near normal.
68
[Cryptorchidism] Behavioral clues of cryptorchid stallion
May show typical stallion behavior such as mounting, penetrating mares, and aggression despite having no scrotal testis (if unilateral or abdominal testis present).
69
[Cryptorchidism] Diagnostic approaches – physical and imaging
Careful palpation of scrotum and inguinal region, plus ultrasound of external inguinal and abdominal cavities to locate retained testis.
70
[Cryptorchidism] Bloodwork findings
testosterone will be baseline, increase Testosterone with hCG stim, estrone sulfate, AMH
71
[Azoospermia] Definition of azoospermia
Complete absence of spermatozoa in the ejaculate.
72
[Azoospermia] Incomplete ejaculation – what to evaluate
Check collection environment (footing, phantom height), AV temperature and pressure, possible pain, environmental distractions, and consider pharmacologic aids.
73
[Azoospermia] Indicators that seminal emission occurred
Gel fraction present and alkaline phosphatase (AP) level in seminal plasma is high (7,000–20,000 IU/L).
74
[Azoospermia] AP thresholds and interpretation
AP <100 IU/L = no seminal emission (e.g., blocked ampullae, retrograde ejaculation). AP 7,000–20,000 IU/L = seminal emission occurred (testicular/epididymal fluid present).
75
[Azoospermia] High AP with no sperm – likely differentials
Testicular degeneration, testicular hypoplasia, or temporary thermal injury affecting spermatogenesis.
76
[Azoospermia] Low AP with complete ejaculation – likely differentials
Blocked ampullae or retrograde ejaculation into the bladder.
77
[Blocked ampullae] Anatomy of ampullae
Widened terminal portion of deferent ducts, surrounded by smooth muscle, responsible for pushing sperm into the urethra.
78
[Blocked ampullae] Clinical signs of blocked ampullae
Azoospermia or very low sperm numbers, high number of detached sperm heads, low AP levels, often following sexual rest and at the beginning of breeding season.
79
[Blocked ampullae] Ultrasound appearance of blocked ampullae
Enlarged ampullae with hyperechoic material in the lumen compared to normal small lumen.
80
[Blocked ampullae] Treatment plan
Massage the glands per rectum, administer oxytocin, and perform serial semen collections (5–7 minimum at season start).
81
[Blocked ampullae] Expected semen findings during resolution
During treatment, expect clumps of sperm, large total sperm numbers, and high percentage of detached heads as blockage clears.
82
[Retrograde ejaculation] Definition in stallions
Semen flows backwards into the bladder rather than out through the urethra due to failure of bladder sphincter closure.
83
[Retrograde ejaculation] Diagnosis of retrograde ejaculation
Collect mid-stream free-catch urine or catheterize bladder after attempted ejaculation and evaluate for sperm.
84
[Retrograde ejaculation] Treatment and prognosis
Imipramine may promote sphincter closure but condition is difficult to manage and not reliably curative.
85
[Azoospermia further DDx] Two major differentials besides blocked ampulla/retrograde ejaculation
Testicular hypoplasia and testicular degeneration.
86
[Azoospermia further DDx] Role of testicular biopsy
Biopsy can differentiate hypoplasia vs degeneration but must be done with caution due to risk to fertility. (never perform this first)
87
[Testicular degeneration – hormones] Early endocrine changes
Increase in estrogen, decrease in inhibin, and increase in FSH.
88
[Testicular degeneration – hormones] Advanced endocrine changes
Decrease in testosterone and increase in LH as Leydig function declines.
89
[Hemospermia] Definition and clinical significance
Presence of blood in semen; erythrocytes are pro-inflammatory in the mare and can cause infertility.
90
[Hemospermia] Clinical presentation
Hemospermia may be obvious (red semen) or subtle; often first detected as reduced fertility.
91
[Hemospermia] Common causes of hemospermia
Squamous cell carcinoma, Habronema lesions, Equine coital exanthema (EHV-3), urethritis, urethral rent, and seminal vesiculitis.
92
[Hemospermia] Diagnostic approach
Full physical exam, semen collection and microscopic evaluation, viral testing/cytology, urethral and bladder endoscopy.
93
[Hemospermia] Treatment principles for hemospermia
Treatment depends on underlying cause; sexual rest is essential and there may be significant financial impact, with some cases requiring surgery.
94
[EHV-3] Equine coital exanthema – agent and transmission
Equid alphaherpesvirus 3; transmitted via fomites and sexual contact, possibly by flies carrying infected vaginal discharge.
95
[EHV-3] Incubation and early lesions
Clinical signs appear 4–8 days after infection; nodules, vesicles, and pustules develop on genital mucosa and rupture.
96
[EHV-3] Typical lesion locations
Vaginal lips and penis are classic sites; lesions can also occur on teats, lips, and nasal mucosa.
97
[EHV-3] Ulceration and healing pattern
Lesions ulcerate and typically heal within ~3 weeks, leaving depigmented white scars.
98
[EHV-3] Systemic signs and fertility impact
No systemic illness; disease does not affect fertility or cause abortion.
99
[EHV-3] Stallion behavior impact
Stallions may be reluctant to breed due to painful genital lesions.
100
[EHV-3] Treatment strategy for EHV-3
Sexual rest and topical antibiotic ointment to prevent secondary bacterial infections.
101
[EHV-3] Breeding status relative to lesions
Stallions should not breed until lesions have healed and scarred.
102
[CEM] CEM causative agent and disease type
Contagious equine metritis is caused by the bacterium Taylorella equigenitalis, a venereal disease.
103
[CEM] CEM transmission routes
Transmitted via live cover, contaminated fomites (including equipment), and artificial insemination.
104
[CEM] Clinical signs of active infection in mares
Vaginitis, cervicitis, endometritis with mucopurulent discharge, possible abortion and infertility.
105
[CEM] Mare carrier state in CEM
Mares may have a non-active carrier state with no obvious clinical signs but still harbor bacteria.
106
[CEM] Clinical signs in stallions with CEM
Stallions are frequently asymptomatic carriers with no obvious clinical signs.
107
[CEM] Carrier state and breed differences
Both mares and stallions may become chronic carriers; transmission patterns differ by breed – high in Thoroughbreds, lower in QH/Warmbloods where extender antibiotics are effective.
108
[CEM] Import and regulatory significance
CEM has major import ramifications; it is a reportable disease and affects semen, embryo, and live horse movement regulations.
109
[CEM] CEM status in Canada
Has not been detected in Canada; strict CFIA regulations and quarantine apply.
110
[CEM] Diagnostic sampling in mares
Swabs from cervix/uterus, clitoral fossa, and clitoral sinus using special swabs and media.
111
[CEM] Diagnostic sampling in stallions
Must swab the erect penis (urethral fossa, urethra, shaft, and prepuce) using appropriate CEM sampling protocol.
112
[CEM] Treatment protocol for CEM carriers
Wash external genitalia with disinfectant soap and apply topical antibiotic ointment (e.g., nitrofurazone or silver sulfadiazine) once daily for 5 days.
113
[CEM] Quarantine measures for imported breeding animals
Quarantine incoming mares and stallions; perform swabs, serology, and test-mare breedings as per regulatory protocols.
114
[EVA] EVA transmission routes
Spread via respiratory secretions, semen, and contaminated fomites.
115
[EVA] EVA clinical signs – general
May be subclinical; can cause respiratory signs and fever associated with panvasculitis.
116
[EVA] EVA edematous clinical signs
Edema of prepuce and scrotum, limb edema, and sometimes urticaria.
117
[EVA] EVA impact on fertility and mares
Fever causes short-term subfertility from thermal damage to sperm; in mares, EVA can cause abortion storms.
118
[EVA] Carrier state in stallions
After infection of a naïve stallion, 10–70% may develop a long-term carrier state.
119
[EVA] Site of latent EVA infection and testosterone link
Latent infection resides primarily in the ampullae; carrier state is testosterone-dependent and reported only in stallions (not mares).
120
[EVA] Route of EVA spread from carrier stallion
In carriers, virus is shed exclusively in seminal fluids.
121
[EVA] Potential spontaneous recovery
Carrier stallions can spontaneously clear the virus over time.
122
[EVA] Effect of EVA on fertility once stable
Carrier state itself has no direct impact on sperm production or fertility.
123
[EVA] Diagnosis of EVA
Based on viral isolation from affected tissues and serology; must also rule out other respiratory or vasculitic diseases.
124
[EVA] Differential diagnoses for EVA
Include EHV-1 & 4, equine influenza, rhinitis viruses, purpura hemorrhagica, equine infectious anemia, allergic urticaria, and hoary alyssum toxicosis.
125
[EVA] Problem with simple serological testing
Positive antibody titers cannot distinguish between vaccination and natural infection; must be interpreted with vaccine history and semen virus testing.
126
[EVA] EVA treatment
Supportive care for affected animals; manage fever, edema, and respiratory signs.
127
[EVA] EVA prevention – vaccination goals
Vaccination prevents infection and carrier state in stallions and prevents infection and abortion storms in mares (although not labeled for pregnant mares).
128
[EVA] Breeding requirement for seronegative mares bred to positive stallions
Seronegative mares must be vaccinated 21–28 days before breeding to an EVA-positive stallion.
129
[EVA] Biosecurity – new animal introductions
Isolate and test new animals for EVA before introducing them to breeding populations.
130
[EVA] Handling freshly EVA-vaccinated animals with pregnant mares
Separate freshly vaccinated horses from pregnant mares due to possible vaccine virus shedding.
131
[EVA] Duration of vaccine virus shedding
Semen may shed vaccine virus for 1–3 days; nasal secretions may shed vaccine virus for up to 7 days.
132
[EVA] Management of seropositive stallions
Management depends on local regulations; bred mares may need to be isolated from the herd after mating to a seropositive stallion.
133
[SCC] Squamous cell carcinoma – frequency in horses
SCC is the second most common tumor in horses.
134
[SCC] SCC behavior and risk factors
SCC is slow to metastasize and is more common in non-pigmented (melanin-deficient) skin and mucocutaneous junctions.
135
[SCC] Common SCC locations in stallions + DDx
Prepuce, penis, and other mucocutaneous junctions; lesions may resemble papillomavirus warts initially.
136
[SCC] SCC diagnosis
Based on clinical suspicion and confirmed via histopathology of biopsied tissue.
137
[SCC] SCC treatment options
Surgical excision with wide margins, excision plus cryotherapy, and intralesional or topical chemotherapy (e.g., cisplatin, 5-fluorouracil).
138
[Testicular torsion] Definition and degrees of torsion
Torsion of the spermatic cord; partial torsions may be subclinical, while 360° torsion cuts off blood supply and leads to gangrenous testicle.
139
[Testicular torsion] Clinical signs of severe torsion
Acute scrotal swelling and colic signs; once testis becomes gangrenous, pain may diminish.
140
[Testicular torsion] Diagnostic landmarks that suggest torsion
Tail of epididymis should be at caudal pole; abnormal orientation suggests torsion. Ultrasound can help confirm compromised blood flow.
141
[Testicular torsion] Treatment of testicular torsion
Usually requires surgical removal (orchiectomy) of the affected testicle.
142
[Paraphimosis] Definition of paraphimosis
Inability of the horse to retract its penis back into the preputial cavity.
143
[Paraphimosis] Causes of paraphimosis
Usually due to edema from trauma or systemic edema in systemic disease; can also result from prolonged dependent swelling or nerve injury.
144
[Paraphimosis] Pathophysiologic progression if untreated
If untreated, swelling and weight of the penis cause venous and lymphatic congestion and can lead to pudendal nerve damage and permanent dysfunction.
145
[Paraphimosis] Diagnosis of paraphimosis
Clean penis, visually assess for lesions or trauma, and use ultrasound if needed to evaluate internal structures and edema.
146
[Paraphimosis] Treatment measures
May include drainage if appropriate, compression and slinging of the penis, topical silver sulfadiazine (SSD) with steroids, massage, NSAIDs, exercise, and hydrotherapy.
147
Red flag findings in stallion BSE
Red flags include: abnormal testicular size/consistency or unilateral absence; total scrotal width <8 cm; low progressive motility (<60%); abnormal AP levels inconsistent with ejaculation; evidence of venereal disease (EHV-3, CEM); significant conformational or hereditary defects; or testicular/penile tumors.
148
Initial workup for azoospermia on BSE
Confirm ejaculation completed (behavior, tail flagging, gel); measure AP; check for blocked ampullae or retrograde ejaculation; assess testes for hypoplasia/degeneration with US and possibly biopsy.
149
Management plan for EVA-seropositive carrier stallion
Confirm carrier status via semen virus testing; vaccinate seronegative mares 21–28 days pre-breeding; isolate bred mares; follow local regulations and advise owner of long-term carrier implications.
150
Steps to reduce venereal disease risk in a stallion station
Pre-breeding cultures (including Taylorella); proper washing of stallions and mares; dedicated breeding equipment; correct use of extenders with antibiotics; quarantine and testing of new imports; adherence to CEM and EVA regulations.
Theriogenology
flashcards
Decks in class (21)
# Cards
-
Review45
-
Dairy 152
-
Dairy 234
-
Dairy 368
-
Beef Cow Repro42
-
Dystocia53
-
Repro Tech43
-
Bull BSE69
-
Male Pathophysiology (ew)97
-
Small Ruminants41
-
Pig Theriogenology73
-
Small Animal 169
-
Small Animal 293
-
Small Animal 359
-
Equine 162
-
Equine 243
-
Equine Lecture 2 - Pathologies33
-
Equine 398
-
Equine 4150
-
Prolapses46
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