Drug Actions-Progesterone

Target Cells:Neurons of

Hypothalamus

Progesterone

Mode of Action:Steroid Pathway

Feedback Mechanism:Negative Feedback

Drug Action-Human Chorionic Gonadotropin (HCG)

HCG Target Cells:Target Cells:OvaryOvary

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

PgFLong estrusOvulation 10 d

PgFEstrus 2-4dOvulation 7-9d

PgFOvulation12-24 hr

PgFFollicle regressesOvulation 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 pregnancyRecent anabolic steroid administrationGranulosa cell tumorWinter 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

• Ovary – No follicular growth– Ovulatory failure– Oocyte quality– Chromosomal

abnormalities

• Oviduct– Blockage– Infection/

inflammation– Failure to pickup

oocyte– Poor environment

Cystic Ovary 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 22-25% Warmblood 20-40% Draft breeds 23% Quarter Horse 10% Arabian 10% Appaloosa 10% Pony 8-10%