Applied Reproduction in the Stallion, Including AI

What is a colt?

• Young entire male <4 years old

What is a stallion?

• An entire or uncastrated male >4 years old

• Two testicles in scrotum

What is a gelding?

Male horse of any age with testicles removed

• Castrated

What age do horses typically reach puberty?

• Age

• ~ 2 years

• Varies (14m-24m)

When do horses typically reach sexual maturity?

• 4 - 5 years

• Max testicular size

• Maximum number pf sperm

In the UK, why are stallions typically kept?

• In UK usually kept entire for breeding purposes

• Now or in the future

• Usually resident on a stud

• Or semen collected at a vet centre

• Pay a service fee - £ depends on the value of the stallion

• But may be ridden with no breeding activity

• Depending on temperament of horse

• Often no contact with mares

Stallions are also _____ breeders.

• Meaning…

Seasonal

• Lower sperm output in autumn/winter

• Can still have semen collected during "off season" for freezing

With stallions being potentially dangerous animals, what special considerations must be made?

• Need special facilities

• Need experienced handlers

• Ensure health and safety of handlers and horses

Not all stallions are very fertile such as __ _____ bred for speed not fertility.

TB stallions

What is stallion grading used for?

• For entry into studbooks

  • Breed approved stallions

  • Require proof of pedigree

  • Graded at grading days

  • Judged according to conformation, performance

    • Not a veterinary exam

  • But sometimes require a 5-stage vetting (Veterinary examination)

    • No hereditary diseases

When performing a breeding soundness exam on a stallion, what characteristics are we looking at for the stallion to posess?

Does a stallion have the mental and physical capability to…

• Deliver semen that contains viable spermatozoa

• Not transfer infectious disease to the mare

• Deliver semen at the correct time

• Establish pregnancy in a reasonable number of mares per season

Breeding soundness exam

• Usually prior to purchase

• To examine prior to breeding season for mare numbers

• Fertility issues

What characteristics of the stallion are examined in the breeding soundness exam?

• General history

• Reproductive history

• The only accurate indicator of fertility is pregnancy rate per cycle (PRPC).

What influences the PRPC?

• PRPC is influenced by 3 main factors:

• Mare fertility

• Stallion fertility

• Management practices

What characteristics do we examine regarding the physical examination in the breeding soundness exam in stallions?

General:

• Body condition

• Musculoskeletal

• Respiratory

• Eyes

• Mouth

What characteristics do we examine regarding the physical examination of the reproductive organs in the breeding soundness exam in stallions?

• Scrotum

• Testicular size & consistency

• Palpation, ultrasound

• Measurement

  • Good correlation with daily sperm output

• Penis

• Often require a mare in oestrus

• Including prepuce

• Internal genital organs

• Palpation, ultrasound

• Observation of libido/mating ability

How do we collect semen from a stallion?

• We can collect semen from a stallion by several means

• Collect into an "artificial vagina" (AV)

• A water filled rubber cylinder with collection bottle at end

• Can alter temperature (range 44-48°C)

• Can alter volume of water in AV

  • alters luminal pressure

• Stallion can mount a jump mare or a phantom mare (Can be trained)

• Can tease with mare is estrus

• Wash penis with warm water + dry

• Need appropriate bridle/head collar

• Dismount sample from a natural cover

• Ejaculated in mare, catch “drips” after

How do we ensure a horse has fully ejaculated?

• Tail flagging

• Palpate pulsation at base of penis

  • Ejaculate passing through urethra

Describe the gross appearance of ejaculate.

• Also note potential issues which may cause discoloration.

• Watery grey to creamy white

• Depends on semen concentration

• Discolouration may be due to contamination

• Dirt/debris from penis

• Inflammatory cells (pus)

• Urospermia (urine in semen)

• Haemospermia (blood in semen)

When performing a semen evaluation, how do we maintain quality?

• Minimise physical trauma, light exposure

• Heat shock/cold shock

Ejaculate has two fractions including:

• Gel fraction

• This is removed by filtration & discarded

• Filtration also removes other debris

• Gel-free fraction

• Contains majority of spermatozoa

• Assessed and usually mixed with semen extender

• Extender based on skimmed-milk or egg yolk and includes antibiotics

  • Help extend the lifespan especially if used for AI

Why might semen volume vary?

• Season

• Sexual stimulation

How do we calculate sperm concentration and total sperm number?

Sperm concentration = millions/mL

volume x concentration = total sperm number

Describe the average semen volume + spermatozoal concentration:

• Semen volume

• Average 50ml (range 10-250ml)

• Spermatozoal concentration

• 100-400 million/mli

• Total number calculated - 4-12 billion

• Longevity of motility variable

What quality of sperm correlates to the greatest fertility indicator?

• Percentage with progressive motility

What are the minimum levels of motility required in sperm?

Is a subjective assessment

• MINIMUM 30-35% Progressive motility required for both chilled and frozen

Describe the three components of the sperm which might be analyzed to determine potential defects.

• The DNA containing sperm head, which is vital to sperm-oocyte interaction

• The head is covered by a cap called the acrosome which stores enzymes needed to penetrate the egg

• The middle piece contains mitochondria to make ATP

• The tail - flagellum provides movement for the sperm

How do we typically stain sperm and what abnormalities might we see?

• Sperm morphology examined with

• Eosin-nigrosin

• Buffered Formalin Saline (wet mount)

• Identify % of normal vs abnormal sperm

• Types of abnormality

• Head defects

• Midpiece defects

• Tail defects

• Cytoplasmic droplets

Describe how frozen semen is packaged and stored.

• Needs extender

• Stored in liquid nitrogen - 196°C

• Packaged in straws

• Need several straws to inseminate a mare

• Thaw before use

• Viability once thawed <12-24 hrs

How long can “fresh semen” last?

• Raw — use direct (within 30 minutes)

• With extender 6-12 hours

How long can “chilled - extended semen” last?

• Over 6 hours and remain motile for up to 72 hours

• But motility deteriorates - ideally <24 hours

What diseases might we look for when performing a breeding soundness exam?

• Testing before start of breeding season - Swabs

• Contagious equine metritis (CEM)

• Other bacteria

Blood Samples:

• Equine Viral Arteritis (EVA)

• Equine Infectious Anaemia (EIA)

• Examine for Coital Exanthema (EHV-3)

What are the main indications for performing castration?

• Indications

• Control of reproduction and sexual behaviour

• Testicular neoplasia

• Testicular trauma

• Inguinal herniation

• Spermatic cord torsion

Usually kept entire with:

• Intent to breed

• Certain competition horses

When do we castrate horses?

• Age

• Can be done at any age (but slight increased risk with age)

• Quicker recovery if younger

• Usually as a colt

• TB usually as 1-2 year olds

• Ponies 6-12 months

• Season

• Usually spring or autumn

• if open scrotal incisions there is risk of myiasis (fly strike) in summer

When performing castration what considerations must be made, regarding the horse’s condition and proper restraint.

• Ensure two testicles

• Animal is healthy

• Tetanus prophylaxis

• Restraint

• Standing

  • Sedation (plus twitch) plus local anaesthesia

• General anaesthesia

• In a field

• Knock down box

• Operating theatre

Where is the safest place to palpate the stallion’s prepuce, penis, etc.

Stand at withers, head up, palpate blindly

Describe how and why an emasculator is used.

• Crush proximally for haemostasis and cut distally

• Principally the spermatic cord

• Used for all castrations

• Nut side is cutting side

• Place "nut to nut"

• Apply for 1-3 minutes

What is a closed castration and how is it performed?

• Vaginal tunic not opened

• Any age, including stallions

• Requires a ligature around spermatic cord

• Requires general anaesthesia

• Skin often left unsutured

What is an open castration and how is it performed?

• Not stallions

• Upper limit of 3-4 yrs

• No ligature

• GA or standing

• "open" via inguinal ring to peritoneal cavity

• Skin left unsutured

What are some potential complications of castrations?

• Oedema/swelling

• Haemorrhage*

• Testicular artery

• Infection

• Protrusion of tissue*

• Eventration/Evisceration*

**Via inguinal ring

• Higher risk with open castration

What is cryptorchidism?

Horse with incomplete descent of one or both testicles

What is a “rig”?

• Lay term for cryptorchid or horse that behaves like stallion with no visible testicles

What is a “false rig”?

• Both testicles removed but behaves like stallion, “odd gelding”

What are the types of chryptorchidism?

• Temporary inguinal retention

• Permanent inguinal retention

• Complete abdominal

• Partial abdominal

Surgical approach for chryptorchid horses depends on location, what are some potential methods?

• Inguinal incision

• Paramedian incision

• Laparoscopy

What is smegma?

• Geldings tend to accumulate smegma as drop penis less often

• Smegma

• A waxy secretion

• Can be excessive

• Can form a 'bean' in the urethral fossa

What is the most common malignant skin tumour in the horse?

squamous cell carcinoma

• initially ulcerative/erosive progressing to granulomatous/proliferative

• Locally invasive but may metastasise

• Can involve dermal tissues and/or internal tissues

• Common sites (mucocutaneous junctions):

• Ocular/periocular tissues

• Genitalia

• penis

• Nares

• Mouth