Non-infectious infertility in the stallion

Question 1

Stallion season

Answer 1

Rate of spermatogenesis and hormone production, and therefore libido decrease in winter

Question 2

Stallion exteroceptive stimuli

Answer 2

Responds to same increases in day length, temperature, food supply as the mare
Stimulated by oestrus mare

Question 3

Spermatogenic cycle

Answer 3

56-58 days - important if anything has affected spermatogenesis

Question 4

Components of fertility exam in stallion

Answer 4

General history
General clinical exam
Bacteriology - urethra, urethral fossa, prepuce swabs
Semen evaluation

Question 5

Congenital fertility problems in stallion (2)

Answer 5

• Chromosomal
• Testicular hypoplasia

Question 6

Behavioural fertility problems in stallion (2)

Answer 6

• Shyness/psychological problems
• Musculoskeletal pain

Question 7

Potential fertility problems in stallion (13)

Answer 7

• Congenital
• Behavioural
• Inadequate erection
• Ejaculatory dysfunction/failure
• Overuse
• Testicular/penile trauma
• Testicular torsion
• Priaprism
• Febrile conditions
• Semen contamination
• Neoplasia
• Endocrinological abnormalities
• Testicular degeneration

Question 8

Chromosomal fertility problems in stallion

Answer 8

Very rare

Question 9

Testicular hypoplasia

Answer 9

Relatively common
Incomplete gonadal development
Unilateral or bilateral
Usually associated with underdeveloped epididymis
Soft or firm consistency
Olio- or azoospermic
Round cells in ejaculate
Libido usually affected

Question 10

Shyness/psychological problems in stallions

Answer 10

Most common in young TB stallions
Reasons:
- Dominated by older mares
- used to being punished for stallion like behaviour
- ‘Handler induced’
Leave alone and loose in yard with 2-3 oestrus mares
Try outdoor covering
Anxiolytic drugs e.g. diazepam
GnRH causes increased LH secretion

Question 11

Musculo-skeletal pain in stallions

Answer 11

Particularly hind leg and back
Causes a drop in libido, ability to mount etc.

Question 12

Inadequate erection

Answer 12

Difficult to differentiate from poor libido
GnRH may help
PGF2a may assist erection

Question 13

Ejaculatory dysfunction/failure

Answer 13

Usually after 7-10 thrusts
Place hand over ventral surface to confirm ejaculation
Alpha-mimetics and/or beta-blockers can treat organic ejaculatory failure
PGF2a may re-initiate ejaculation process
Xylazine can be used to induce ejaculation
Imipramine has been used

Question 14

Overuse of stallions

Answer 14

Common in first season TB stallions, may be in ageing stallions with testicular degeneration
Semen is watery and grey, smaller volume, less motile sperm, and much lower concentration of sperm
Reduce covering load, cover each mare only once with good oestrus management, ensure he is well fed
If ageing insert subcut low dose GnRH implant
If not TB consider AI

Question 15

Testicular/penile trauma

Answer 15

Inflammation, heat, haemorrhage, and swelling of scrotum and/or sheath
Drainage often impeded as well as gravity making the oedema worse
Paraphimosis - the inability to retract the penis back into the prepuce then may occur
Reduce inflammation and try o improve venous and lymphatic drainage

Question 16

Potential sequelae of penile/testicular trauma

Answer 16

• Production of abnormal sperm
• Production of anti-sperm antibodies
• Intra-scrotal haemorrhage or haematocele leading to permanent testicular damage
• Hydrocele may develop

Question 17

Testicular torsion

Answer 17

180 degrees - common in ponies, asymptomatic, not a problem
360 degrees - very acute, severe colic, emergency

Question 18

Priaprism

Answer 18

Persistent penile erection
Use of acepromazine is a risk factor
Treat similarly to paraphimosis

Question 19

Febrile conditions

Answer 19

General illnesses causing a rise in body temperature for a few days can result in a temporary depression of fertility 1-3 months later

Question 20

Semen contamination

Answer 20

Haemospermia: trauma, urethritis, accessory gland infection etc. can be diagnosed on visual inspection of the urethral process, palpation and US of accessory glands, endoscopy of urethra. Treat with sexual rest, antibiotics, flush via scope or catheter
Urospermia: a neurological problem, diagnose based on colour, smell, pH, urine crystals. Get the stallion to urinate before covering

Question 21

Neoplasia in stallions

Answer 21

Squamous cell carcinomas of the penis are relatively common
Neoplasia of the testes are rare - seminoma being the most common, Teratoma is found predominantly in cryptorchid testes

Question 22

Endocrinology abnormalities in stallions

Answer 22

Check LH and testosterone levels as an indication of normality
Impotent stallions tend to have lower blood concentrations of LH whereas concentrations of testosterone tend to be similar to normal stallions
Slow stallions can be treated with low levels of testosterone or GnRH