Diagnostic methods in the stallion Flashcards
What tests would you run in the stallion prior to breeding?
- Bacteriological screening
- Virology/vaccination for venereal pathogens
- Semen evaluation
- Ultrasonography
- Urethroscopy
- Further tests:
- ?Testicular FNA cytology
- Cytology
How many samples do you need for bacteriological screening in the stallion?
Low Risk’ Stallion
2 negative sets of swabs 7 days apart
‘High Risk’ Stallion
* As above
* Plus screen 4 mares post mating
Remember:
Swabs from urethra, urethral fossa, sheath and pre-ejaculatory fluid
What if venereal pathogens are isolated on bacteriological screening of a stallion?
Topical – Cleaning of the Penis
* 50% acetic acid (Pseudomonas)
* Hydrochloric acid (Pseudomonas) 10ml of 38% in 4 litres water
* Sodium hypochlorite (Klebsiella) 45ml of 5.25% in 4 litres water
* Care about transmission to buckets / sponges etc
Topical antimicrobial agents on the basis of sensitivity
* 90% Pseudomonas sensitive to polymixin
* 90% Klebsiella sensitive to neomycin
Inoculate from broth from normal stallion
* e.g. Treat for 5 days and inoculate on days 6 and 8
Re-test according to Guidelines
How is equine viral arteritis spread? How is it controlled?
NOTIFIABLE DISEASE
Virus present in semen
* Infection of mares venereally
* These mares develop respiratory tract infection
* Virus is spread to other mares which if pregnant will abort
* There is no treatment for these stallions except castration - Because 30% OF STALLIONS SHED VIRUS IN SEMEN FOR LIFE (virus harboured in accessory glands)
Control
* The problem is it can be difficult to differentiate serologically an infected stallion from a vaccinated stallion (have to resort to repeated semen collection and virus isolation)
* Therefore if you vaccinate a stallion it is imperative that you demonstrate he is serologically negative prior to vaccination and that the vaccination results in a positive serological response (and you document this on the vaccination certificate)
What vaccinations and serological testing are important in stallions?
- Vaccination for Equine Viral Arteritis
- Vaccination for Equine Herpes Virus 1
- Inspection negative for signs of Equine Herpesvirus 3 (Equine Coital Exanthema)
- Serologically negative for Equine infectious anaemia (EIA) for horses returning to UK - N.B. EIA is notifiable in the UK
- Quarantine on entry to stud to demonstrate no signs of Strep Equi (Strangles) develop
What palpation would you include in your clinical exam of the stallion?
- Palpation of the testes and epididymides
- Palpation of the inguinal canal
- Palpation and inspection of the penis
Why do you need to remove the gel fraction of the semen before evaluating it?
Removal of Gel Fraction by filtration or suction because gel:
* Reduces sperm motility
* Interferes with vital staining
* Makes pipetting of sperm difficult
* Reduces longevity of the sample
What drug can be administered to astallion to cause epididymal contraction?
Alpha 2 agonist
What factors determine sperm output?
- Age
- Season of the year (40% increase during breeding season)
- Frequency of ejaculation (only DSO is available)
- Testicular size (T.bred normal 10 x 6 x 5 cm)
- Appreciate that semen quality varies throughout the year
What are the characteristics of normal stallion semen?
- Colour of ‘dish water’
- Volume: 15 to 100 ml
- Concentration: 50 - 700 x 106 sperm per ml
- TSO: 400 - 800 x 106 sperm
- Motility: 60 - 80% IFPM
- Morphology: 60% live normal sperm
Describe normal appearance of testes on ultrasound - what measurement can be undertaken?
- Echogenic capsule
- Hypoechoic parenchyma
- Bright echogenic stipples
- Echogenic mediastinum testis
- Use for measurement of testicular size and volume
- Formula for the volume of an ellipse = 4/3 pi (a x b x c)
What do generalised and focal changes in testicular echotexture indicate?
Generalised changes in testicular echotexture
* Often representing cellular infiltration
* Fibrosis (testicular degeneration)
* Haemorrhage
* Oedema
* Inflammation / infection
Focal changes in testicular echotexture
* Neoplasia
* Cysts
* Spermatocoele
Why would you do direct impression smears of the penis for cytology?
Penile tumours
What is haemospermia? Why does it occur? How is it treated?
- Reduction in fertility associated with whole blood within the ejaculate
- Reduced fertility probably caused by reduced sperm motility due to sperm agglutinating with RBCs
Aetiology
* Bacterial urethritis
* Accessory gland infection
* ?penile laceration / tumour
Treatment
* Systemic antibiotics and NSAIDs
* Sexual rest
* Urinary acidifiers
What are possible leisons of the sheath?
- Phimosis
- Paraphimosis - Of which traumatic paraphimosis is very important
- Priapism
- Sarcoid
- Melanoma
- Posthitis
What is phimosis? What causes it? What clinical signs are associated? How is it treated?
Small preputial orifice
Causes
* Usually congential
* Occasionally acquired following trauma
* Sometimes following penile enlargement (neoplasia) such that there is size mis-match
Results in failure of penile protrusion
Common signs are pooling of urine and urine dribbling
Treatment
* Surgical as described for the dog
* Treat penile disease
What is paraphimosis? What causes it? How is it treated? What can be a consequence?
Failure to retract the penis
Causes:
* Trauma during breeding
* Phenothiazines (as part of priapism syndrome)
Results in marked gravity oedema to the penis and drying of the penile surface
Treatment
* Critical aspect is to establish whether the horse can urinate
* Don’t catheterise it if very traumatised
* If seen early try to reduce the size of the penis by using pressure bandages and massage
- If penis can be returned to sheath then keep it in place using purse-string suture
- If penis cannot be returned to sheath then prevent gravity oedema by supporting the penis
- Towel under penis and tied over back, or pair of ladies tights
* Clean the penis daily and apply lubricant
* If the penis skin splits then fluid is released and this is your chance to replace the penis
* Otherwise may need to provide support for up to 3 weeks
* Surgery is unlikely to be necessary
* Never operate on an oedematous penis – it wont heal
Consequence
- Sometimes after healing there is chronic scar tissue producing pain on erection or erection failure
What is priapism? What can cause it? How is it treated?
Persistent enlargement of the penis in the absence of sexual excitement
Causes
- Normally phenothiazine tranquilisers
* Not uncommonly when stallions are sedated to take swabs for venereal pathogens
* Or, when sedated for other reasons
* IF YOU EVER SEDATE AND CAUSE PENILE PROLAPSE YOU MUST MAKE SURE THAT THE PENIS IS RETURNED TO THE SHEATH BEFORE YOU LEAVE. IF IT IS NOT THEN REPLACE IT AND HOLD IT IN PLACE EVEN USING TOWEL CLIPS AS A TEMPORARY MEASURE.
- The problems is always worsened as soon as the penis is out for a period of time and it develops gravity oedema
Treatment
* If the penis is turgid and not retracted
* Attempt manual replacement
* Place towel clips or sutures across sheath
* Take clips off at 12 hours and re-check
* If the priapism is permanent it may be necessary to amputate the penis
What horses are most prone to melanomas? How are they usually managed?
- Older grey stallions
- Usually little consequence unless it influences penile protrusion and breeding - usually left
Which horses are commonly affected by sarcoids? How are they managed?
- More frequent in younger horses
- Nodular appearance if large can influence penile protrusion and breeding
- Topical cytotoxic drugs can be useful but need to be aware of potential for scarring and how this will affect function of sheath
What is prothitis? What can cause it?
Inflammation of the sheath may occur at the same time as inflammation of the penis
Common causes include
* Coital exanthema (see later)
* Bacterial overgrowth (usually associated with penile neoplasia or FB)
* Fly-strike (a common clinical presentation is mild colic signs)
