Drug Actions-Progesterone
Progesterone
Feedback Mechanism:
Negative Feedback
Target Cells:
Neurons of
Hypothalamus
Mode of Action:
Steroid Pathway
Drug Action-Human Chorionic
Gonadotropin (HCG)
HCG
Target Cells:
Ovary
Mode of Cellular Pathway:
2nd Messenger-cAMP
Feedback:
Positive (increase P4)
Percentage of mares ovulating at various
time intervals after administration of hCG.
Hormone Management
• Prostglandins
– Only works on mature
corpus luteum (~ 5 d
after ovulation)
– Mare will come into
heat 2-5 days later.
– The time to estrus
varies depending on
follicular development
on the ovary.
• Lutalyse
– Dose is 5-10 mg (1-2
cc/mare) IM.
– Side effects
• Estrumate
– Dose is 200 mcg/mare
IM.
– Fewer side effects
Single Prostaglandin Injection
• Prostaglandin during luteal phase results in heat ~3 days, ovulation
in 3-16 days
• Response rate of ~50%
• Mares with excessive side effects can get same results w/ 1/10
dose
PgF
Long estrus
Ovulation 10 d
PgF
Estrus 2-4d
Ovulation 7-9d
PgF
Ovulation
12-24 hr
PgF
Follicle regresses
Ovulation of new
In 9 d
Mare Evaluation
Diagnostic tests & things to
consider
• Age, physical condition, &
history of mare.
• Examination of the mares
external reproductive
conformation.
• Palpation of uterus.
• Speculum exam of the
cervix.
• Culture of uterus.
Mare Evaluation
Diagnostic tests & things to consider
• Examination of uterine cells (Cytology).
• Endometrial biopsy.
• Ultrasonography
– Diagnosis of delayed uterine clearance.
• Endoscopy: visually inspecting inside the uterus.
• Oviduct blockage exams.
Uterine Biopsy
• Category I – No pathological changes and
should be of normal fertility. Estimated foaling
rate = 80-90%
• Category IIA & IIB -Inflammatory changes
severe enough to decrease fertility and may be
accompanied by fibrosis. Estimated foaling rate
= 50-80%
• Category III-Drastically reduced fertility. Uteri
may be incapable of supporting fetal
development. Estimated foaling rate = <10%
Poor Perineal Conformation
• Common in older mares
• Associated with endometritis
• Management
– Caslick’s procedure
Reasons Why A Mare May Not
Come In To Heat
• Lactation anestrus
• Silent heat
• Multiple ovulations
Reasons Why A Mare May Not
Come In To Heat
• Diestrous ovulations
Reasons Why A Mare May Not
Come In To Heat
• Persistent corpora lutea,
Reasons Why A Mare May Not
Come In To Heat
Abortion after day 35 of pregnancy
Recent anabolic steroid administration
Granulosa cell tumor
Winter anestrus & spring transition
Old vs Young
• Reduced pregnancy
rates, higher EED
• Fewer oocytes/embryos
collected
• Oviductal embryos
smaller & of reduced
quality
• Uterine embryos reduced collection rates
and quality, delayed
development
• 15-20 years
– shorter follicular phase
– smaller follicles
– more double ovulation's
• 20+ years
– longer follicular phase
– intermittent ovulation's
– failure to ovulate
Mare Infertility
• Oviduct
• Ovary
–
–
–
–
No follicular growth
Ovulatory failure
Oocyte quality
Chromosomal
abnormalities
Cystic Ovary
– Blockage
– Infection/inflammati
on
– Failure to pickup
oocyte
– Poor environment
Ovarian hematoma
Uterus
• Inflammation
• Infection
• Fibrosis (scar
tissue)
• Poor environment
• Mechanical
Endometritis
• Inflammation of the
tissue lining the
uterus
• Usually associated
with infection
• Predisposing Factors:
– Poor perineal
anatomy
– Trauma (parturition
or breeding)
– Inadequate hygiene
– Failure of uterine
defense
mechanisms
(especially uterine
motility/clearance)
Inflamed cervix of a young,
nulliparous mare 5 hours
after intrauterine infusion of
bacteria. Donated by Dr
John Hughes
Endometrial Cysts
•
•
•
•
Obstructed/dilated lymphatics
Common in older mares
Risk to pregnancy is low
Confused with pregnancy on ultrasound
Cervix
•
•
•
•
Tears
Adhesions
Fibrosis
Inflammation
Vagina, vulva, vestibule
•
•
•
•
Urine pooling
Air
Vaginitis
Foreign material
Urine Pooling
• Most common in older
mares
• Urine refluxes forward
into vagina
• Urine enters cervix during
estrus and may pass into
uterus
• Results in endometritis
and infertility
• Treatment
– Correct
predisposing factors
– Uterine lavage
– Urethral extension
surgery
Infectious Infertility in Mares
 Signs
 Irregular estrus cycles
 Anestrus
 Matted tail hair & crusty
hair on hindquarters
 Failure to conceive
 Visible, slimy milky or
creamy white exudate on
vulva, tail, inner thighs,
vaginal floor
 Red mucus membranes
Primary Causes of Abortion
• Twins
– Abortion generally
occurs in late
pregnancy (7
months to term)
• Equine herpes
virus
• Placentitis
Factors affecting
incidence of twins
• Breed
• Reproductive status
– lower incidence in
lactating mares
• Age
– higher incidence in
older mares
• Repeatability
• Heredity
Incidence of multiple
ovulation's
Thoroughbred
Warmblood
Draft breeds
Quarter Horse
Arabian
Appaloosa
Pony
22-25%
20-40%
23%
10%
10%
10%
8-10%