Equine infertility

Question 1

What are some DDx for causes of infertility in a mare? (8)

Answer 1

True temporary anoestrus (e.g. seasonal)

True permanent anoestrus

Transitional oestrus

Silent oestrus/behavioural anoestrus

Irregular oestrous cycles

Ovarian tumours (GTCT)

Endometritis (4 types)

Retention of endometrial cups

Question 2

What is a silent oestrus in a mare? What are some causes?

Answer 2

Cycle (±OV) w/o showing behavioural/overt signs of oestrus

• foal at foot > lactational anoestrus dt concern for foal
• any stress = transport, introduction into a new flock

Question 3

What actions can be taken in a mare suspected of having silent heats?

Answer 3

Adjust teasing technique

Synchronise cycle (PGF2a)

AI (if OV is dx’d by US)

Question 4

What are some causes of true temporary anoestrus in mares?

Answer 4

Seasonal anoestrus (winter)

Systemic disease

Anabolic steroid tx (illegal in racehorses)

GnRH vaccine

Question 5

What causes retention of endometrial cups? Why does this cause acyclic activity?

Answer 5

Loss of a foal after d35 of pregnancy (when cups form)

• cups cause accessory CL growth > maintain high P4 until d120 of pregnancy
• mare won’t cycle that season

Question 6

How is retention of endometrial cups dx’d in both:

• a mare who has just lost a foal?
• a mare who lost a foal last season?

Answer 6

A - Blood eCG test + ovary US (accessory CLs)

B - hysteroscopy (–> tx by ablation of cups)

Question 7

What are some causes + associated clinical signs of true permanent anoestrus?

Answer 7

Chromosomal abnormalities (if never cycled before) = masculine behaviour, external genital abnormalities

Question 8

What is the most common ovarian neoplasia in mares? Are these tumours generally hormonally active or inactive?

Answer 8

Granulosa theca cell tumour (GTCT)

Active tumours secrete:

• testosterone OR oestrogen
• inhibin
• AMH

Question 9

What are some clinical signs of a GTCT?

Answer 9

Behavioural changes (dependent on what hormones are produced)

• testosterone → stallion-like behaviour
• oestrogen → nymphomaniac
• none → anoestrus

Question 10

How are GTCTs diagnosed? what test + what signs?

Answer 10

Physical exam + behavioural signs

Examine ovaries by rectal palpation/US

• GTCT = enlarged, polycystic/honeycomb, no OV fossa
• other ovary = very small (dt inhibin prod’n by GTCT)

Blood tests = inhibin (+++), AMH (+++)

Question 11

What mechanism causes the unaffected ovary to be hypoplastic in a horse w a unilateral GTCT?

Answer 11

Neoplastic inhibin prod’n → suppression of FSH prod’n in anterior pituitary → no follicular activity in unaffected ovary

Question 12

What is the treatment for a GTCT?

Prognosis for breeding soundness?

Answer 12

Unilateral ovariectomy (mid-ventral laparotomy)

Good Px but takes 6-8wks for cyclicity to resume (TF may lose the season)

Question 13

Ddx for enlarged ovaries

Answer 13

GTCT (benign)

Teratoma - contain teeth/hair

Ovarian adenocarcinoma (malignant)

Ovarian haematoma

Question 14

Ddx for irregular oestrus cycles

Answer 14

Transitional oestrus (at beginning of the breeding season)

Anovulatory haemorrhagic follicles (AHF)

Persistent CL

Question 15

What is an anovulatory haemorrhagic follicle (AHF)?

Answer 15

Dominant follicles which fail to ovulate then fill with unclotted blood + P4-producing luteal cells

Question 16

Why does blood in an AHF fail to clot?

Answer 16

Anticoagulants in follicular fluid

• this differentiates an AHF from a corpus haemorrhagicum (clotted blood)

Question 17

What are some risk factors for an AHF?

Answer 17

Older mares

Transitional oestrus

Question 18

What is the tx for an AHF?

Answer 18

PGF2a injection to induce luteolysis

• may take longer to respond than a regular CL TF ≥ 1 dose may be necessary

Question 19

What is a persistent CL?

Answer 19

Any CL which lasts longer than 13-16 days (length of luteal phase in mares) → failure to come back into heat

Question 20

What are the 3 possible causes of a persistent CL?

Answer 20

Dioestral ovulation

Chronic endometrial disease (no endometrial fcn = no PGF2a)

EEL following conception (CL persists til d70)

Question 21

What is the tx for a persistent CL?

Answer 21

Induce luteolysis = PGF2a

Question 22

What pathogens are most commonly involved in endometritis in mares?

Answer 22

Opportunistic pathogens = commensals of genitals of mare/stallion

• Streptococcus equi zooepidemicus
• E. coli

Venereally-tm’d pathogens =

• Taylorella equigenitalis (CEM)
• Klebsiella pneumoniae
• P. aeruginosa

Question 23

When/how do pathogens gain entry to the uterus to cause endometritis?

Answer 23

Veterinary uterine exams (if poor asepsis)

Poor MCT during AI procedure

Joining to a stallion

Question 24

What are some non-bacterial causes of endometritis?

Answer 24

Fungal infections - Candida, Aspergillus, Mucor

Iodine/ABs

Air (pneumovagina)

Urine (urovagina)

Question 25

What uterine defence mechanisms protect against infectious endometritis?

In what stage of the oestrous cycle are these mechanisms impaired + why?

Answer 25

PMNs (Mø + neuts) = phagocytic cells

Cilia of endometrial cells

Secretory Ab (IgM/IgA)

Muscle contractions = ejection of uterine contents

Impaired in dioestrus:

• P4-induced immunosuppression
• Closed cervix/no muscle contraction/no flushing = no drainage

Question 26

What anatomical barriers protect against infectious agents reaching the uterus?

Answer 26

Vulval lips

Vestibulo-vaginal sphincter

Cervix

Question 27

What methods of Dx of endometritis are available?

Answer 27

Breeding history of infertility

Clin signs = vaginal discharge (often on tail)

Clitoral swabs (any time) → cytology/C&S (only excludes STIs as many commensals in clit fossa)

Endometrial swabs (during dioestrus) → cytology/C&S (dx of all agents - should be sterile environment)

Endometrial Bx → histopathology

Question 28

Tx of endometritis

• timing during cycle?
• when to next breed?

Answer 28

Flush uterus w saline (+ OXT to contract uterus)

• tx during oestrus = open cervix + good defences
• when flush runs clear → antimicrobial tx
  
  • intrauterine NS ABs
  • systemic BS ABs (TMS)
  • antifungals
  • povidone-iodine flush (vs. fungi)
• breed mare on same oestrus (using MCT)

Question 29

What is endometrosis?

What Dx method?

What are the consequences?

Answer 29

Degenerative endometrial changes dt chronic endometritis

• irreversible
• fibrosis stroma
• degeneration of endometrial glands

Dx = Bx/histopathology

Leads to poor endometrial blood supply + formation of endometrial cysts

Question 30

What do endometrial cysts indicate in a mare?

Answer 30

Poor lymphatic drainage dt fibrosis of the endometrium

Question 31

What is the end-stage consequence of endometrial fibrosis?

Answer 31

Transluminal adhesions

Question 32

What is persistent mating-induced endometritis (PMIE)?

Answer 32

Persistence of endometrial inflammation > 4-5d post-service

• normal endometrial inflamm following joining lasts 1-2d
  
  • bacteria on stallions penis + spermatozoa
  • cleared by uterine defences
• persistence = inflammatory uterine environment → embryo can’t survive when it enters at d4-5 post-OV

Question 33

What is a ‘susceptible mare’?

Answer 33

Any mare which does not clear uterine infllammation by 2d post-joining

• Premature PGF2a release → short inter-OV interval
• Persistent endometritis = infertility (as embyro can’t survive inflamed environment)