stallion: Semen analysis and breeding soundness evaluation

The only accurate indicator of fertility is

Pregnancy rate per cycle

What factors influence pregnancy rate per cycle?

Mare fertility, stallion fertility, management practices

Why may we want to evaluate stallion semen?

Part of breeding soundness exam, estimate number of services, prior to sale or purchase of a new stallion, processing of semen, fertility problems, prior to inseminating a mare

When do male horses reach puberty?

~2 years of age

When do male horses reach sexual maturity (Maximal testicular size, maximum number of sperm)?

4-5 years

What are features of a breeding soundness exam?

History and ID including type of breeding, previous BSEs, previous breeding seasons foaling rates, stallion management, and illnesses, medications, etc

Physical exam including assessing Lameness, joint checks, back, conformation, vision, and heritable conditions

How can we collect a semen sample for anaylsis?

Artificial vagina, dismount sample after natural cover, chemical stimulation (xylazine)

What from a mare stimulates the stallions?

Lack of progesterone - indicates natural estrus

What gross appearance are we looking for in stallion ejaculate?

Watery grey to creamy white

Discoloration may be due to contamination (dirt/debris, inflammatory cells, urospermia, hemospermia)

Why should we count the ejaculate sperm numbers?

Allows determining number of doses and volume of extender to add

We want ~500million motile sperm per mare

Semen gets diluted in semen extenders for shipping and freezing

What are features of hemocytometer counting for sperm?

Inexpensive, time consuming, raw or extended. Accurate (potential for operator errors)

What are features of spectrophotometer counting for sperm?

Beam of light passes through sample, light absorbance is inversely correlated to the concentration. (Lower light going through → higher concentration within sample)

If contamination present, can cause errors

What are features of nucleocounter counting for sperm?

Fluorescent probe with propidium iodide, binds to DNA, provides accurate and repeatable counts.

Semen extenders do not interfere

Expensive option

What semen motility is required for commercial distribution?

30-35% progressive for both chilled and frozen

Where is the DNA contained within sperm?

The head

What covers the head of sperm that contains enzymes needed to penetrate the egg?

Acrosome

What is contained within the middle section of the sperm?

Mitochondria to make ATP

What aprt of sperm provides movement?

The tail (flagellum)

When assessing morphology, what abnormalities can we see?

Head defects, midpiece defects, tail defects, cytoplasmic droplets

What are potential causes of hemospermia?

Trauma to repro tract, urethral rent, neoplasia, seminal vasculitis, habronemiasis

How can we diagnose a cause to hemospermia?

Careful examination of repro tract, use endoscopy

How can we treat hemospermia?

Sexual rest for traumatic rents or tear (4-6w), consider surgical repair

How can we diagnose a pyospermia?

Post washing assess prea nd post-ejaculate

Urinalysis, palpation and ultrasound (for seminal vasculitis and epididymitis)

How can we treat pyospermia?

NSAIDs and antibiotics

What substances are in the pre-sperm ejaculate?

Bulbourethral gland contents

What portion is sperm-rich in the ejaculate?

First three jets

What makes the substances in the sperm-rich ejaculate?

Testes, epididymis, ampullae

What portion is sperm-poor in the ejaculate?

Remaining jets

What makes the substances in the sperm-poor ejaculate?

Seminal vesicles and prostate

What makes the substances in the gel fraction of the ejaculate?

Seminal vesicles

What are features of sperm production in the stallion?

Continuous process throughout the year (takes two months from full loss to normal levels)

If temp is elevated, sperm may be altered within a few days

During a breeding soundness exam, what must we ensure we examine accurately in regards to the reproductive tract?

Penis, External genitalia, Testes (palpation, measurement, caliper ± US)

In general, larger testes make

more sperm

What are features of Daily sperm output?

Compare calculated with actual levels (can aid identification of stress, injury, or semen quality changes)

This value varies with age, testicular health, and season

What is necessary to measure daily sperm output?

Collect daily for 7-10 days (to deplete storage within the tail of epidymis)

OR

Collect twice in one day, second collection one hour after should estimate this value

What are signs of testicular dysfunction?

Declining function, decline in sperm output, decreased pregnancy rates, decreased in testicular size, change in texture

What pathogenic bacteria should we be concerned to find on a stallion penis?

Taylorella equigenitalis, Klebsiella pneumoniae, pseudomonas aeroginosa

What sites should we swab if concerned for bacterial infection on/near the penis?

Urethral sinus, free portion of penis, urethra, urethra pre-ejaculatory fluid

What equine herpes virus strain is a concerning veneraeal disease?

EHV-3

What are features of EHV-3?

Causes equine coital exanthema

Self-limiting (resolves in 2-4w), breeding may be affected, transmission to mares

What condition are stallions natural reservoirs for?

Equine viral arteritis (EVA)

What are the rates of venereal transmission of EVA?

85-100%

What are clinical signs of EVA?

Pyrexia, anorexia, peri-and supraorbital edema, edema of prepuce ± scrotum, temporarily infertile, persistently infected then no effect on semen quality

How can we diagnose EVA?

Viral isolation in semen, serology searching for viral neutralization (pair of samples 3-6w apart)

What is the treatment for EVA?

None for pneumonia

Biosecurity measures, screen semen, vaccinate colts at 6 mo, vaccinate mares pre-breeding to a positive stallion