Lecture 26- Stallion Breeding Soundness Exam

When should a stallion breeding soundness examination (BSE) be performed?

Prior to breeding season, during pre-purchase exams, when fertility declines, and routinely with semen evaluations at collection

What is the purpose of a stallion breeding soundness examination?

Estimate the stallion's present fertility

What are the major components of a routine BSE?

Reproductive history, physical exam, venereal disease testing, genital evaluation, cultures, sexual behavior assessment, semen collection, and semen evaluation

What venereal diseases are specifically evaluated during a BSE?

Equine Infectious Anemia (EIA) and Equine Viral Arteritis (EVA)

What semen characteristics are routinely evaluated during a BSE?

Motility, morphology, concentration, volume, and longevity

What advanced tests may be performed beyond a routine BSE?

Sperm function testing, biochemical assays, urethral endoscopy, DSO, genetic testing, testicular biopsy/FNA, and test breeding

What physical abnormalities may impair mating ability?

Lameness, back pain, and neurologic abnormalities

What heritable conditions are important during a stallion BSE?

Cryptorchidism, parrot mouth, wobbler syndrome, and exostosis

How should EVA screening be performed in stallions?

Annual serologic testing

What is recommended if a stallion is seronegative for EVA?

Consider vaccination of the stallion

If a stallion is seropositive for EVA, what should be done next?

Culture the semen

What should be done if EVA-positive stallion semen cultures are positive?

Test mares before breeding

If a mare is seropositive for EVA, is vaccination required?

No

If a mare is seronegative and bred to an EVA-positive shedding stallion, what is recommended?

Vaccinate prior to breeding

If semen cultures are negative for EVA, are vaccines necessary?

No

What should be assessed during external genital examination?

Presence of two testes, mobility, tone, symmetry, skin abnormalities, and normal orientation

What is the normal orientation of the testes?

Cranial-to-caudal with epididymal head cranial and tail caudal

What structures are evaluated ultrasonographically during a BSE?

Testes, testicular parenchyma, epididymides, spermatic cords, and scrotal contents

How is testicular size measured?

Total scrotal width using calipers or ultrasound

What total scrotal width is expected in a mature stallion?

Greater than 100 mm

Until approximately what age do stallion testes continue growing?

About 5 years of age

When are stallions considered sexually mature according to testicular growth?

Approximately 5 years of age

What is the relationship between testicular size and sperm production?

Testicular size is correlated with daily sperm output (DSO)

What penile structures are emphasized in the learning objectives?

Free portion of penis, urethral sinus, urethral process, and urethral fossa

Where is the free portion of the penis located?

Distal exposed portion extending beyond the prepuce

Where does the prepuce attach to the penile shaft?

At the attachment of the inner lamina of the preputial fold to the penis

What common penile abnormalities should be recognized during BSE?

Lacerations, balanitis, squamous cell carcinoma, melanoma, and habronemiasis

What transport media may be used for aerobic culture samples?

Stuart, Amies, and charcoal media

From which locations are aerobic cultures commonly obtained?

Prepuce, urethral fossa, urethra (pre/post ejaculation), semen, and glans penis

What organisms are considered part of normal penile/urethral flora?

Proteus spp., Staphylococcus spp., Aerobacter spp., E. coli, and Streptococcus spp.

What culture result is expected in normal stallions?

Mixed bacterial growth

Which bacterial organisms automatically fail a stallion on a BSE?

Pseudomonas aeruginosa, Klebsiella pneumoniae, β-hemolytic Streptococcus, and Taylorella equigenitalis

What disease is caused by Taylorella equigenitalis?

Contagious Equine Metritis (CEM)

What culture pattern automatically fails a BSE regardless of species present?

Heavy growth of a single organism

Why are bacterial cultures important in stallions?

Stallions are often asymptomatic carriers of venereal pathogens

What methods may be used for semen collection?

Artificial vagina, condom, manual stimulation, pharmacologic ejaculation, standing collection, phantom, and jump mare

What is a "rusty load"?

Cleanout ejaculate collected before official collection

What two factors are artificial vaginas most sensitive to?

Pressure and temperature

What internal temperature should an equine artificial vagina maintain?

45-48°C

What are the three major artificial vagina types discussed in this lecture?

Colorado, Missouri, and Roanoke

What is the major advantage of the Missouri AV?

Lightweight and easier penile manipulation

What is the major disadvantage of the Colorado AV?

More difficult to manipulate the penis

What is the major advantage of the Colorado AV?

Better heat retention due to heat-sink effect

What additional advantage does the Colorado AV provide?

Fits inside a phantom for breeding simulation

What is the major characteristic of the Roanoke AV?

Lightweight design

What special consideration exists when removing a Roanoke AV?

Wait until the bell of the penis decreases in size

What are the benefits of phantom collection?

Increased safety and controlled semen collection

What disadvantage still exists with phantom use?

Injury can still occur

Why must phantoms often be adjusted?

Different stallions require different positioning

What mare may be needed to facilitate phantom training?

A mare in estrus

What reproductive behaviors are assessed during a BSE?

Temperament, libido, erection, mounting, intromission, and ejaculation

What is the Flehmen response?

Characteristic curling of the upper lip during scent investigation

What behavioral signs commonly accompany reproductive interest?

Prancing, vocalization, and biting

What can self-mutilation in a stallion indicate?

Neurologic disease or pain

What management methods may be used as negative reinforcement?

Stallion rings, whips, and discipline

Which mare-associated stimuli affect stallion behavior?

Diestrus status, coloration, and vocalization

What are the three ejaculatory fractions in stallions?

Pre-sperm, sperm-rich, and gel fractions

What gland contributes most to the pre-sperm fraction?

Prostate

What is the purpose of the pre-sperm fraction?

Cleans the urethra

Which fraction contains most spermatozoa?

Sperm-rich fraction

Which structures contribute to the sperm-rich fraction?

Epididymis, ampulla, and prostate gland

What is the appearance of the sperm-rich fraction?

Milky

What structures contribute to the gel fraction?

Vesicular glands and bulbourethral glands

What is the appearance of the gel fraction?

Clear gel

What is the function of the gel fraction?

Flush remaining sperm from the urethra

How long does spermatogenesis take in the stallion?

55-57 days

How long does epididymal maturation and transport require?

Approximately 9 days

What period of time does an ejaculate represent?

Approximately the previous 2 months

What components are included in gross semen evaluation?

Color, clarity, and volume

What is the normal color of stallion semen?

White

What abnormal semen colors may be encountered?

Yellow or red

How is normal semen clarity described?

Milky

What semen appearances may be observed during gross evaluation?

Watery, milky, or creamy

What factors influence semen volume?

Season and teasing

What is the average stallion ejaculate volume?

44 ± 28 mL

Why is sperm motility important?

Positively correlates with fertilizing ability

What cellular characteristics are reflected by motility assessment?

Membrane integrity, mitochondrial function, and flagellar function

What two motility measurements are commonly reported?

Total motility and progressive motility

What unique feature of equine sperm explains circular movement patterns?

Abaxial attachment of the head to the midpiece

Is circular sperm movement in stallions considered abnormal?

No

What minimum progressive motility is expected in a satisfactory breeder?

Greater than 60%

What is considered the gold standard for sperm concentration determination?

Manual hemocytometer count

What dilution is commonly used for manual sperm counting?

1:100 dilution in formalin-buffered solution

What instruments can be used to determine sperm concentration?

Hemocytometer, densimeter, CASA, nucleocounter, and Spermacue

What contaminants can falsely increase concentration measurements?

Urine, blood, dirt, and debris

What stains are commonly used for sperm morphology evaluation?

Eosin-nigrosin and Diff-Quik

At what magnification is morphology typically evaluated?

1000× oil immersion

How many sperm cells are generally evaluated for morphology?

100

How are sperm morphological defects classified?

Normal, primary defects, and secondary defects

What percentage of sperm should be morphologically normal?

Greater than 60%

What round cells may be observed in semen?

Spermatogenic cells, neutrophils, and giant multinucleated cells

What alkaline phosphatase concentration indicates a true ejaculate?

Greater than 3,000 U/L

What does a low alkaline phosphatase concentration suggest?

Not a true ejaculate or incomplete contribution from testicular/epididymal sources

What is the normal semen pH range?

7.2-7.7

What is the normal semen osmolarity?

336 ± 10.5 mOsm

Why is urea nitrogen measured in semen?

Assess urine contamination

What stall-side test may assess urea nitrogen?

Azostix

What does PMMNS stand for?

Progressively Motile Morphologically Normal Spermatozoa

How many PMMNS are considered the minimum for a satisfactory potential breeder?

1 billion in the second ejaculate

What criteria define a satisfactory breeder?

Normal libido/gait, two testes, no genital abnormalities, scrotal width ≥8 cm, normal culture, and ≥1 billion PMMNS