Stallion/Colt Fertility Assessment

Question 1

What is the range of numbers of mares which a stallion may be expected to cover in a season?

Answer 1

1 – 200 mares

Question 2

What steps are involved in assessing a stallions reproductive capacity?

Answer 2

History - general & reproductive
Physical exam (including MSK assessment)
Observation of sexual behaviour & mounting behaviours (in both natural + AI-directed stallions)

Question 3

What pathology samples should be collected from a stallion during a reproductive exam?

Answer 3

Pre- & post-ejaculatory swabs for culture - urethra, penis, prepuce
Fluid samples - semen, accessory gland fluid
Blood/serum (for viral analysis - EIA, EVA, EHV-3)

Question 4

What bacterial pathogens are common causes of stallion reproductive disease? How are these detected?

Answer 4

Pseudomonas aeruginosa
Klebsiella pneumoniae
Taylorella equigenitalis (CEM)

Dx = culture of swabs from reproductive organs

Question 5

What viral pathogens are common causes of stallion reproductive disease? How are these transmitted & how are they detected?

Answer 5

Equine infectious anaemia (EIA)
Equine viral arteritis (EVA)
Equine herpesvirus-3 (EHV-3)

Tm = venereal
Dx = serology

Question 6

What is involved in a testicle exam in stallions?

Answer 6

Total scrotal width (TSW)

Question 7

What is the average width & length of the stallion scrotum?

Answer 7

Avg width = 110 mm (range 50-150mm)

Avg length = 80-140 mm

Question 8

Why is total scrotal width important? What does it measure?

Answer 8

TSW measures testicular size, TF sperm production/output

• healthy large testes = more sperm production
• beware pathological enlargement

Question 9

Formula - Daily sperm output (DSO)

Answer 9

DSO (billions) = 0.2 x (total testicular V) – 1.26

Question 10

How long is the sperm production cycle? Why is this important?

Answer 10

60 days

- insult to testicles/seminiferous epithelium > decreased sperm output for 60 days (TF rest the stallion)

Question 11

What methods can be used to expose the penis for examination?

Answer 11

Expose the stallion to a mare

Sedate with xylazine/ACP

Question 12

What structures should be examined during the external part of the physical exam of the penis?

Answer 12

Penis
Urethral process
Fossa glandis + diverticulum of fossa glandis

Question 13

What structures should be examined during the internal part of the physical exam of the penis? How are they examined & what aspects are considered?

Answer 13

Pelvic urethra
Body of the prostate
Seminal vesicles (vesicular glands)
Bulbo-urethral glands
Ampullae

Exam by palpation + endoscopy
Look at size + consistency

Question 14

What accessory sex glands are present in the stallion?

Answer 14

Ampullae (terminal ductus deferens)
Vesicular glands
Prostate gland
Bulbourethral glands

Question 15

What methods are available to collect semen from a stallion?

Answer 15

Artificial vagina - using a dummy/surrogate mare
- requires good training & preparation

Never use electroejaculation in horses

Question 16

How should the artificial vagina be prepared for semen collection?

Answer 16

Temp = 42-48 deg C
Pressure
Lubrication

Protect sample from cold shock & sunlight & contamination

Question 17

What parameters are considered when examining a semen sample in-field?

Answer 17

Volume of ejaculate
Colour
Density
Debris
pH of sperm (7.2-7.9)
Wave motion = rapid swirling

Question 18

What parameters are considered when examining a semen sample in the lab?

Answer 18

Sperm count (automated)
Sperm cell morphology
Bacterial cultures (CEM, pseudomonas, klebseilla)

Question 19

What could cause morphological abnormalities in sperm?

E.g.’s of sperm morphological abnormalities

Answer 19

Obstruction to sperm flow/stenosis of tubes
Sperm stasis

Proximal cytoplasmic droplet
Kinked tail
Head abnormalities

Question 20

What is the most accurate test of stallion fertility?

Answer 20

Pregnancy rate per mare cycle (>75%)

Question 21

What are some advantages of AI over natural service?

Answer 21

No stallion transport required = dec Tm of STIs + able to remotely serve
Breeding possible w incompatible stallion/mare (size, temperament etc.)
Minimum contamination breeding technique
Quality control/monitoring of stallion semen quality