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Alterations in sexual function- MARE
Veterinary Medicine

Additional Veterinary Medicine Flashcards




Breeding soundness exam of the mare

1. History

2. physical exam

3. examine the external genitalia

4. examine internal tract

5. vaginal exam

6. endometrial swab



  1. General 


    Usual mngt routine such as housing/feeding Current use

  2. Reproductive history
    Oestrus cycle documentation: eg length, behaviour, observability Breeding dates: AI or natural
    Foaling date if foal at foot
    History of endometritis: treatment and outcome 



  1. Physical Examination 



  1. General clinical examination

  2. Lameness examination

  3. Look for evidence of heritable defects 



  1. Examination of External Genitalia 





1. Perineal/vulval conformation

Good: Vulval lips are vertical (80-90o is normal). Lips are closely apposed making a good seal. ≥80% vulvar lips below level of ischium

Fair: Vulval lips inclined <80o. Lips are apposed making a good or reasonable seal.

Poor: Vulval lips are inclined < 80o. Poor or ineffective seal. >50% vulval commissure is above the bony brim with a sunken anus - requires Caslick's vulvoplasty

  1. Pneumovagina: “windsucker" testpart vulval lips and listen for air entering vestibule

  2. Discharge: signs on hindquarters and tail? During oestrus there may be urine crystals dried on the mare's vulva. These should not be confused with a pathologic discharge.


2 lateral clitoral sinuses with single central fossa

  1. Located on surface of clitoris

  2. Can harbour CEM organism (Taylorella equigenitalis) or other venereally

    transmissible organisms (Klebsiella pneumoniae and Pseudomonas aeruginosaClitoris may be swabbed at this stage - use minitip swab in Amies charcoal media, check swab in date and send to accredited laboratory

Mammary glands: mastitis, abscesses, sarcoids, melanomata 



Examination of Internal Tract (by trans-rectal palpation) 



  1. Cervix

    1. Tone should correlate with cycle stage: relaxed in oestus, turgid in

      dioestrus (NB opposite to cattle)

    2. Maiden or aged mares may not relax fully in oestrus

  2. Uterus

    1. Pregnancy

    2. Size of uterus

    3. Tone

    4. Location

  3. Ovaries

    1. Size

    2. Follicles and perhaps corpus haemorrhagicum (cannot palpate corpora lutea)

    3. Presence of ovulation fossa


examine of internal tract ( by transrectal ultrasonography)


  1. Uterus
    1. Pregnancy

    2. Endometrial cysts -record size, shape and location

    3. Uterine fluid - appearance and amount

  2. Ovaries

    1. Follicles
    2. Corpora haemorrhagica
    3. Corpora lutea
    4. Anovulatory haemorrhagic follicles 5. Neoplasia/ovaian haematomata 



Vaginal Examination 



  1. Speculum: Use sterile speculum with sterile, water-soluble lubricant

    1. Varicose veins

    2. Urovagina

    3. Perineal tears

    4. Hymen remnants

    5. Appearance of external os of cervix (may suggest stage of cycle)

  2. Digital examination

    1. Cervical tears / adhesions - most easily done during dioestrus

    2. Perineal tears

    3. Cervical tone (open in oestrus, closed in dioestrus) 

Endometrial swab


use double-guarded swab to avoid contamination

  1. Restrain and tail-wrap mare

  2. Wash perineum with antiseptic solution, rinse and dry

  3. Sterile gloves with sterile, water-soluble lubricant 



Common Isolates (in order of probability)

  1. Beta haemolytic streptococci spp

  2. E. coli

  3. Other Enterobacter

Less common but possible isolates

  1. Pseudomonas auruginosa

  2. Klebsiella pneumoniae (Capsule types 1,2 & 5)

Pure heavy growth is more likely to be significant than light mixed growths, which are likely to be contaminants. The interpretation of culture results is best done with the cytology and /or ultrasound findings in mind to be most useful. For example if the culture is positive (small number of colonies) and the cytology results are negative (normal epithelial cells), the culture is likely to be a contaminant. 



Cytology sample can be obtained in one of three ways:

  1. Using a small volume uterine flush. 60ml of sterile isotonic saline flushed into

    the uterus and then aspirated. This is then centrifuged and placed onto a

    slide. (time consuming)

  2. Using a double guarded swab, which is then ‘rolled’ onto a slide. It is possible

    to use the swab also for endometrial culture if the slide is sterile.

  3. Using a plastic disposable ‘cup’ to scrape the surface of the endometrium

  1. Stain with Diff-Quik (Modified Wright-Giemsa)

  2. Look for sheets of epithelial celss to confirm an adequate sample has been

taken. The presence of neutrophils (>1/10 epithelial cells) indicates endometritis.

NB. It is not possible to assess stage of cycle using cytology in the mare 



Endometrial Biopsy (often performed if other tests inconclusive) 



A. Use endometrial or rectal biopsy forceps and suitable restraint
B. Easiest to perform during oestrus but easier for lab to interpret during dioestrus C.
Put into Bouin’s medium (supplied by lab)
D. Can diagnose

  1. Endometritis

  2. Periglandular fibrosis

  3. Cystic glandular distension 



  1. Endoscopic Examination (not used routinely) 



  1. Endometrial cysts

  2. Transluminal adhesions

  3. Neoplasia leiomyoma most common uterine tumour 



  1. Blood sampling 



  1. Progesterone: to confirm dioestrus (also raised in pregnancy)

  2. Anti-Mullerian Hormone: best current test for GCT

  3. Testosterone/inhibin: raised in about 50% of GCT’s

  4. Oestrogen: not commercially available

  5. Chromosomal karyotyping: should be 64XX,
    most common abnormalities are 64XO/64XY 

Fertility problems in the mare

1. failure to show signs of oestrous

2. persistent oestrus 

3. failure to become pregnant 


failure to show signs of oestrous

a) Small ovaries

b) Enlarged ovary 

c) Normal sized ovaries 



Failure to show signs of oestrus

  1. Small Ovaries 



  1. Winter anoestrus: most common reason early in year.

  2. Hypoplasia: chromosome abnormality rare

  3. Atrophied ovaries: due to age, emaciation, parasitism, disease, stress 

Failure to show signs of oestrous- enlarged ovary


  1. 1. Ovarian neoplasm: Granulosa (Thecal) Cell Tumour (GTCT):

    2. Anovulatory haemorrhagic follicle

    3. Haematoma   



  1.  Ovarian neoplasm: Granulosa (Thecal) Cell Tumour (GTCT): 

most common ovarian tumour in mare but adenoma/adenocarcinoma/cystademona also reported
Ovarian neoplasm clinical signs


Hormones produced by the tumour may cause behavioural changes, including stallion-like behaviour. Normal regular cycling will be altered/cease. 

ovarian neoplasm diagnosis


Palpation and ultrasonography of an abnormally enlarged ovary (>10cm) with a atrophied contralateral ovary (<4cm) Negative feedback by the secretion of inhibin on the hypothalamus and pituitary cause regression of the opposite ovary to a small, inactive structure. Ovulation fossa of affected ovary obliterated.

Histology of removed ovary
Hormonal assays
Anti-Mullerian Hormone test of choice previously used Inhibin A (80%), Testosterone (50%) 

Ovarian neoplasm treatment


Unilateral ovariectomy used to be done by transvaginal colpectomy or laparotomy but now usually done laparoscopically. May take up to a year for other ovary to regain function, but fertility should be normal. 



Anovulatory Haemorrhagic Follicle



Anovulatory Haemorrhagic Follicle: follicle matures as normal but then fails to ovulate, filling with blood and usually eventually developing luteal tissue. May be refractory to prostaglandins for several days or weeks, preventing mare from coming back into season. 






Haematoma: uncommon, may or may not be associated with trauma 

Normal sized ovaries


1. Pregnancy: always check this first if mare failing to show signs of season! 2. Silent heat: cycle progresses as normal but mare does not show signs of

3. Failure of luteal regression: PGF2a from uterus fails to cause luteolysis at

day 15
4. Early embryonic loss: mare conceives but embryo lost before first scan

takes place
5. Dioestrus ovulation: occasionally ovulation takes place in mid-dioestrus

during mini ‘wave’ of follicles, Cl formed too late to be lysed by PGF2a @ day 15 

persistent oestrous


  1. Spring/autumn transitional period: mare develops follicles but they do not ovulate. May last for 2-6 weeks. In Scotland, about 50% of mares will still be in transitional stage in April.

  2. G(T)CT: oestrus is a rare clinical sign of GTCT, due to the absence of the hormone Aromatase. Without this hormone, oestrogen cannot be produced from androgens. 

Failure to become pregnant


  1. Endometrial Transluminal Adhesions

    B. Endometrial Cysts 

     c. Endometrosis

    d. endometritis 

Endometrial transluminal adhesions


  1. Endometrial Transluminal Adhesions

    1. Aetiology: trauma, parturition, caustic agents (eg chlorhexidine/iodine scrub)

    2. Diagnosis: uterine endoscopy. Bands, sheets or tunnels seen

    3. Treatment: breakdown manually or with laser but may recur. Alternatively use

      biopsy forceps + endoscope or laser 



  1. Endometrial Cysts 



  1. Occurrence: Presence, size and location should be noted when seen as can be mistaken for early pregnancies. May interfere with pregnancy if multiple, very large or extensive and prevent embryo contacting the entire uterus. Small isolated cysts rarely a problem. Clusters common.

  2. Aetiology: coalescence of lymphatic lacunae. Small cysts may be caused by cystic glandular distension.

  3. Clinical signs and diagnosis: cysts detected in uterus by ultrasonography.

  4. Treatment: surgical excision possible in some cases; can use biopsy

    instrument to break down walls; electrocautery; laser removal. But most cysts do not require treatment. 



  1. Endometrosis (NB not the same as endometriosis) 



  1. Refers to non-inflammatory chronic pathology of the endometrium

  2. Incidence increases with age

  3. Commonly associated with endometritis as reduces resistance to infection

  4. Diagnosed on endometrial biopsy

  5. Decreases ability to conceive and carry a foal to term

  6. No effective treatment available

  1. Histopathological changes include:

    1. (i)  periglandular fibrosis: fibrotic changes surrounding uterine glands

    2. (ii)  lymphatic lacunae: poor myometrial activity fails to pump the lymph fluid as

      normal and lacunae develop 



  1. Endometritis:  



  1. nflammation of the endometrium

    Probably the most common cause of sub-fertility in the mare.

    Can be divided into 3 general types: 



Venereal disease: 



Sexually transmitted diseases such as Contagious Equine Metritis. 



Chronic Uterine Infection (CUI):



predisposing factors usually present



Persistent Mating-Induced Endometritis (PMIE) 



a prolonged excessive reaction to




Contagious Equine Metritis (CEM)  



very rare occurrence in UK

Clitoral fossa and sinuses of all mares should be swabbed prior to going to stud/natural service. 

CEM aetiology


  1. Taylorella equigenitalis (CEMO) - NOTIFIABLE DISEASE

  2. A gram negative microaerophilic coccobacillus

  3. Venereal transmission and contaminated equipment and handling

  4. Organism persists in clitoral sinus of carrier mares 

CEM Clinical signs and pathology


  1. Severe endometritis, necrosis and shedding of the epithelial lining of

    the uterus

  2. Profuse, watery, mucopurulent, non-clumping discharge from uterus

  3. Short oestrous cycle (8 to 12 days)

  4. Stallions are inapparent carriers (just have surface contamination) 

CEM diagnosis


  1. Isolation of Taylorella equigenitalis from reproductive tract

  2. Culture system chocolate agar with increased CO2 (5 to 10% CO2)

  3. Approved laboratories only certified to test for this 



  1. Treatment:

    1. Many cases recover spontaneously but carrier status MUST be assessed.

    2. Some fail to recover despite treatment

    3. Some require treatment - uterine infusion for several days with

      antibiotics; topical wash of clitoral fossa with 2% chlorhexidine

    4. Pack external genitals with nitrofurazone or chlorhexidine ointment

    5. Clitoral infections can be hard to treat consider clitorectomy /

      sinusectomy in very difficult cases. 

Chronic uterine infection


1. Aetiology: Normal, resistant mares are able to clear bacteria from the uterus quickly. Susceptible mares have decreased uterine resistance and remain persistently infected after bacteria are introduced into the uterus. May be due to failure of uterine contractility or uterine immune defence mechanisms. Failure in the 3 ‘seals’ (vulval lips, vestibulovaginal junction, cervix) will allow infection to gain access to uterus.

Infection is introduced by:

  1. Pneumovagina

  2. Urovagina

  3. Parturition

  4. Copulation

  5. Veterinary gynecological procedures

  1. Causative organisms

    1. Beta-haemolytic streptococci (S. zooepidemicus - 90%)

    2. E. coli

    3. Pseudomonas aeruginosa

    4. Klebsiella pneumoniae (capsule types 1, 2 and 5)

    5. Yeasts (Candida spp)

    6. Fungi (Aspergillus spp

chronic uterine infection: clinical signs


  1. Discharge from vulva / uterus

  2. Fluid in uterus on ultrasound

  3. But these visual clinical signs can be absent so consider if failing to conceive

d. May have a shorter dioestus period than the 15 days usually expected 

chronic uterine infection diagnosis


  1. Culture of uterine swabs

  2. Histological (from biopsy) or cytological (from smear) changes



chronic uterine infection treatment



  1. Short cycle mare with PGF-2 [image]to bring into oestrus - oestrogens

    have positive effect on uterine immune defence mechanisms.

  2. Administer oxytocin IV or IM

  3. Lavage uterus with 0.5-1l sterile Hartmann’s solution or saline to

    manually remove contamination

  4. Infuse uterus with appropriate antibiotics (generally use systemic

    dose), such as neomycin/penicillin, framomycin or ceftiofur (all off


  5. Repeat treatment for 3-5 days

  1. Correct any predisposing conformational abnormalities e.g


    vulvoplasty - see below

  2. Maintain good hygiene during examinations and breeding. Use AI if




Persistent Mating-Induced Endometitis 



1. All mares will have an immunological reaction to semen and produce uterine fluid but normal mares will expel /absorb this fluid at the same rate as it is produced

2. Free intra-uterine fluid accumulates and clinical signs and diagnosis as are for CUI 3. Treatment involves oxytocin, flushing and antibiotics but must be started after

sperm have reached the oviduct (4 hrs post-insemination) and before the fertilized ovum descends into the uterus (5 days post-insemination) 



Conformational factors predisposing to endometritis


1. pneumovagina

2. urovagina 



"windsucking"): air in vagina with or without faecal contamination.

1. Aetiology:

  1. Poor vulvar and perineal conformation

  2. Thin, flaccid, gaped vulvar lips

c. <80o angle of vulva (80-90

angle is normal) d. >50% vulvar lips above level of ischium

  1. Sunken anus

  2. Damaged perineal region from trauma at parturition

  3. Seen commonly in thin mares

  4. In some mares, may occur only during oestrus

  1. Diagnosis:

    1. Gurgling, blowing sound when lips of vulva are parted

    2. Foamy, frothy exudate in vaginal cavity

    3. Severe cases may balloon uterus

  2. Treatment: Caslick's vulvoplasty. Infiltrate vulvar margins with local anaesthetic from just below level of ischium to the dorsal commissure. Remove a 0.5 cm strip of mucosa. Suture dorsal portion of vulvar lips together. Remove sutures after 10 days. Must be reopened before parturition. 



accumulation of urine in the vagina.

  1. Aetiology:

    1. Poor perineal conformation

    2. Relaxed ligaments

    3. Extreme weight loss

  2. Clinical signs:

    1. Urine in vagina

    2. May occur only during oestrus

    3. May occur transiently post partum

  3. Diagnosis: speculum examination

  4. Treatment:

    1. Surgical urethral extension

    2. In some mares, may be able to swab the urine out of the vagina

      immediately before breeding and, once the cervix closes, pregnancy can be maintained. 

Advancing the oestrous cycle


Mares are seasonally polyoestrus:

Winter anoestrus

  •   Spring/autumn transitional periods

  •   Summer oestrus/dioestrus cycles

    The breeding season for racing Thoroughbreds starts February 15 and ends July 1. This means that a considerable portion of the breeding season is before mares begin to cycle regularly. It can also be advantageous for other types of horses to begin to cycle earlier than they otherwise would, so techniques have been developed to advance the breeding season:

    1. Artificical control of photoperiod

    2. Transitional breeding season  

artificial control of photoperiod


  1. Provide natural or artificial light from 8am to 10pm (so a 14:10 hour ratio)

  2. Start at end December to initiate transitional period by end February

  3. Enough light must be present to comfortably read a newspaper throughout the

    stable usually a single 100W bulb will achieve this 

Transitional Breeding season


  1. Lasts 30-60 days on average

  2. Waves of follicles develop and regress without ovulating, giving prolonged

    and irregular periods of oestrus activity

  3. Cervix partially open

  4. Mares will irregularly tease positive for long periods

  5. The end of transition is marked by an LH surge and ovulation.

  6. Onset of normal cyclicity may be hastened by

    1. Altrenogest (synthetic progesterone) orally daily for 10-15 days

    2. Human Chorionic Gonadotrophin (hCG) IV

b. Exogenous GnRH - deslorelin implant or twice daily injections of


the normal cycle


Hypothalamus: GnRH (slow pulses)
Pituitary: FSH release
Ovary: Follicular growth > Dominant follicle/s > Oestrogen production > Effects on behaviour and repro tract > +ve feedback to hypothalamus
Hypothalamus: GnRH (fast pulses)
Pituitary: LH release
Ovary: Ovulation > Formation of CH then CL > Progesterone production from CL > - ve feedback to hypothalamus

Interovulatory interval of 18-24 days (average 21)
Oestrus lasts 3-8 days, dioestrus 14-18 days
Follicles grow during oestrus. Usually one follicle (occasionally two) will become dominant and ovulate >40 mm.

There is also a smaller mid-dioestrus ‘wave’ of follicle growth.
PGF2a is released by endometrium at about day 15 if no embryo is detected

Day 0: ovulation, CH forms
Day 5: fully functional corpus luteum
Day 15: CL lysed by PGF2a, one or two dominant follicles develop
Day 18: standing oestrus begins
Day 0: ovulation


Mares are bred..


Traditionally mares are bred on day 2 or 3 of oestrus and then every other day until the end of oestrus. Mares should be bred prior to ovulation when a dominant follicle (>30 mm) is present. If it is necessary to limit the number of breedings, the ovaries should be palpated daily and breeding should take place just prior to ovulation. If ovulation has occurred, good conception rates may still be achieved by breeding 12-18 h after ovulation. However incidence of early embryonic death increases with post-ovulation breedings due to fertilization of an aged ovum. 

pharmacological agents used for cycle manipulation


  1. Progestogens

    2. prostaglanding F2

    3. Oestradiol

    4. human chorionic gonadotrophin

    5. GnRH 



  1. Progestogens



  1. synthetic oral solution (altrenogest). Oestrus occurs 4-5 days after withdrawal. May be used short term to synchronise a mare or long term to suppress oestrus behaviour. 



  1. Prostaglandin F2



  1. used to lyse a CL allowing mare to return to oestrus 2-5

    days later. CL must be between 5 and 14 days old to respond. Ovulation is variable (3-10 days) depending on follicular development at time of treatment. Natural PGF2a (Lutalyse) causes more side effects (sweating, colic, muscle

    cramping which subside in 30 min) than the synthetic preparations

    (Estrumate, Prosolvin) . 

not available in the UK


  1. Human Chorionic Gonadotrophin (hCG) 



  1.  LH-like activity

    Can hasten ovulation of a mature follicle.
    1500 iu IV or IM will cause ovulation of a >35 mm follicle in 36-48 h.
    The mare may mount an immune response to sequential doses inactivating the compound. 



  1. GnRH



  1. Buserelin: given to cause ovulation of mature follicle , use IM 6 hrs before service, ovulation is expected within 2 hours.
    Deslorelin: is a GnRH analogue which induces ovulation of a 35 mm follicle in 36-48 h. It is administered as a short-term implant placed subcutaneously in neck or vulval lips and is most useful in frozen semen AI when a short ovulation interval is advantageous. 

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