Infertility in the Mare
LECTURE 5
Introduction
 Extrinsic Factors
 Lack of Use
 Sub-fertile Stallion
 Poor management
 Intrinsic Factors
 Many, many, many
Age
 Reported to have the most significant bearing on
reproductive performance
 Decrease in fertility may be in part due to

An increase in transit time for sperm to reach the oviduct
 Anovulatory estrus is greater in mares over 20
 Placental development and blood supply are also
adversely effected
Chromosomal Abnormalities
 Normal Chromosomal Number?

64 or 32 pairs

Female = 64XX
Variations of a normal compliment include

63XO – female with single X chromosome
 Turner’s syndrome – common chromosomal
abnormality
 Characterized by small ovaries
 Poorly developed uterus
 Permanent anestrous

Hormonal Abnormalities
 Hypothalamic – pituitary – ovarian homeostasis



Majority of hormonal deficiencies are associated with:
Pituitary abnormalities
Can cause:
Prolonged estrus
 Prolonged di-estrus
 Silent ovulations
 Can eventually lead to reproductive failure


Synthetic Progesterone has proved successful in treatment
Follicular Atresia
 Defined:
 Break-down of the ovarian follicles
Group of follicles will develop normally to
 ~3 cm in diameter
 Failure in the emergence of a dominant follicle


Causes may include
 Ovarian hypoplasia (underdevelopment or incomplete
development)
 Ovarian cysts
 Infections, and malnutrition

Time appears to be best cure
Corporal Lutea Persistence
 Creating long or short estrous cycles
 Normal lifespan of CL is 14d
 In the absence of pregnancy, PGF2α is secreted
 A persistent CL is presumably present due to the
failure of the release of PGF2α
 Could be due to uterine infection
 Treatment with exogenous PGF2α is normally
successful
Anovulatory Follicles
 Can be a cause of anestrous
 Commonly occur in transition periods into
and out of breeding seasons
 Anovulatory follicles are characterized as
 Large follicles which fail to rupture and ovulate
 Fill with blood and persist as hematomas over a
number of cycles
 Presence is further complicated with their ability to
secret progesterone
Granulosa (theca) cell Tumors
 Most common tumor within the equine ovary
 Important cause of anestrous
 Normally effect mares between the ages of 5 and 7
 Usually associated with one ovary
 Ovaries are usually polycystic or large solid structures
 May weigh up to 18 pounds
 Symptoms may cause
 Prolonged Estrus
 Testosterone producing cysts may cause:


Stallion Like Behavior
Muscular development
 Removal of ovary may lead to normal reproduction
Ovarian Abnormalities
 Ovarian Teratomas
 Arising from germ cells
 Contain hair, teeth, bone, etc.
 Very rare
 Hypoplasia
 Underdevelopment
 Small, immature ovaries
 Often associated with chromosomal or hormonal
abnormalities
Ovarian Abnormalities
 Multiple Ovulations
 Results in multiple pregnancies
 Major cause of abortion
 Mare is typically unable to carry twins to term
Infectious Infertility
 Endometritis
 Major cause for infertility in the mare
 Inflammation of the uterine endometrium
 May be caused by:
 Opportunistic Bacteria
 Venereal bacteria
 Non-Infectious Agent
 Major problem with infection is
 Often undetected for long periods of time
 Difficult to treat
Opportunistic Bacteria
 Streptococcus zooepidemicus
 Implicated in 75% of acute endometritis
 Cause destruction of RBC
 Major role in initiating infection of cervix and uterus
 May promote proliferation of other bacteria
 Hemolytic Escherichia coli
 Second most common cause of uterine infection
 Can cause acute endometritis but also severe systemic
infection
Opportunistic Bacteria
 Staphylococcus aureus
 Less common
 May invade reproductive tract under stress
Venereal Bacteria
 Transferred solely via venereal route
 Present within the semen and reproductive
tract of both mare and stallion
 Some horses may be asymptomatic
 Three main type:
 Taylorella equigenitalis
 Klebsiella pneumoniae
 Pseudomonas aeroginosa
Venereal Bacteria
 Taylorella equigenitalis

Extremely Contagious

First isolated in England

Stallion is not effected but


Prime means by which it is spread
In mare
Acute endometritis
 Discharge within 2 – 5 d of infection
 May appear to recover but remains carrier
 May also be asymptomatic

Venereal Bacteria
 Klebsiella pneumoniae
 Acute and chronic endometritis
 Little to no clinical signs present
 Relatively insensitive to antibiotics
 Pseudomonas aeroginosa
 Can be found in stallion’s semen
 Clinical symptoms rare
 In mares
 Yellow to green discharge
 Relatively resistant to antibiotics