Estrous cycle in mare

MVDr. Markéta Sedlinská, Ph.D.

Equine Clinic, University of Veterinary and Farmaceutical Sciences, Brno

Female reproductive tract

Female reproductive tract

The normal estrous cycle

Seasonally polyestrous breeders (75-80 % mares)

(Arabian 1/1, equator ↑ % year-round cyclicity)

The ovulatory phase

the period from first ovulation in the spring until the last ovulation in the

autumn

Anestrus

the period of ovarian activity during the winter months

Transition

the period of irregular or prolonged estrus receptivity that occurs in early

spring or late autumn

Anestrus

Described as sexually dormant

the ovaries are small, smooth and firm with no palpable follicular activity or functional luteal tissue

uterus atonic, thin-walled

mucose membranes pale, dry, no obvious secretions

cervix relaxed

plasma progesteron less than 1 ng/ml

Transition phase - spring

re-estabilishment of endocrine function

erratic sexual behavior

follicle development without accompanying ovulation

enlarge ovaries

follicles 1- 3,5cm , regress

No corpus luteum!

little physical change

in the reproductive tract

uterus flaccid, thin walled

End of the transition:

The first follicle of the year that ovulates is accompanied by uterine edema and

development of corpus luteum

Transition phase - autumn

decreasing photoperiod

has the reverse effect on

the mare to the increasing

photoperiod in the spring

behavior and ovulation

become more erratic

after last ovulation –

regress, no grow...

The ovulatory phase

Dynamic grow of follicles

3.5 – 6 cm

ovulation → corpus luteum CL

Estrous cycle

+/-21 days (from ovulation to ovulation)

follicular phase (inconsistent) and luteal phase (15 days)

estrus 2 – 10 days (14 days)

duration of the estrus

spring (longer) x autumn (short)

individuality of the mare

influence of inflammation and pathologic condition

Factors affecting the reproductive cycle of the mare

Photoperiodicity

Condition, body condition score

temperature

age

Hormons of reproductive organs

Photoperiodicity

the effect of day lenght are mediated negatively by melatonin secretion from the pineal gland within the brain

hight melatonin secretion suppress GnRH release from hypotalamus

no GnRH = no FSH, LH = no follicules, no estrus

Body condition score, temperature of environment, age of the mare

BCS

6-9 / from 10 points

Flushing

3 weeks before season

hair

finish moulting

Age

Puberty – first ovulation (1 - 1,5 year)

breeding age – 3 years and older

too old maiden mare syndrome! ( closed cervix)

Hormons of reproduction

GnRH Gonandotropine releasing hormon

FSH Follicle stimulating hormon

LH Luteinizing hormon

estradiol - estrogen

progesteron

PG Prostaglandin F2α

Estrus

Diestrus

ESTRUS

Follicle • > 3.5 cm

Uterus

Cervix

behaviour

ESTRUS

Follicle

Uterus • edema of endometrium

• typical folds

Cervix

behaviour

ESTRUS

Follicle

Uterus

Cervix • relaxed

• opend

• at the bottom of vagina

behaviour

ESTRUS

Follicle

Uterus

Cervix

behaviour

Mating

sexual maturity

breeding maturity

physical maturity

young (up 8 years) x old mares

natural service

artificial insemination

fresh x chilled fresh x frozen semen

Breeding by naturale service

☺ natural!

☺ stallion in situ

☺ reliable detection of estrus

☺ good even for subfertile stallions

transport of mare (foals!)

↓ hygiene, ↓ security

less number of covered mares

transmission of infections

Arteficial insemination

☺ availability of stallion

☺ easy transport

☺ ↑hygiene, ↑ security

☺ ↑number of mares

no risk of transmision of infections

detection of estrus and ovulation

not usefull for subfertile stallions

Artificial insemination

Artificial insemination