Mare Reproductive Physiology

Colin Mitchell BVM&S CertEP MRCVS

Hexham

Content

• Anatomy ( structure )• Physiology (function )• When to breed• Expectations• Pregnancy diagnosis• Twins

Puberty

• Onset of reproductive activity

• Occurs at 12 – 24 months of age

• Well –fed spring born fillies reach puberty in their second spring

• Variable factors

Mare Anatomy

• 2 ovaries• Y – shaped uterus /

womb• Cervix• Vulva• Breeding Soundness

Examination

Physiology

• Ovaries • Oestrogens• Progesterone• Influence behaviour

and reproductive tract

Physiology

• Follicles grow on the ovaries and release oestrogen

• Once follicles mature – ovulation

• Release of ovum (egg)

Physiology

• Structure remaining is the corpus luteum (CL)

• Progesterone produced from CL

Physiology

• Winter Anoestrous• Transitional Period• Oestrus • Dioestrous

Winter

Spring

Summer

Summer

Transitional Period

• After winter anoestrous

• Before seasonal polyoestrous ( breeding season )

• Long, irregular oestrous cycles

• Low levels of oestrogens, no ovulation

• Numerous follicles present on ovaries

Oestrous

• Oestrous cycle usually 21 / 22 days

• Period of sexual receptivity – 5 /6 days

• Affected by daylight ( April – Oct )

• Behaviour due to absence of progesterone

• Ovulation takes place between 24 – 48 hours before end of oestrous

• Follicles usually 35 – 50 mm at ovulation

Oestrous Signs

• Stands to be mounted• Raises the tail• Leans towards stallion

/ does not kick• Everts the clitoris

( winking )• Squats and urinates

Dioestrous

• Lasts 15 days• Presence of CL• Production of

progesterone• Actively rejects

stallion

When to breed

• Natural breeding within a cycle

• Early breeding season• Foal heat

Breeding methods

1. Pasture breeding

2. Hand breeding

3. Artificial Insemination

Hand Breeding

• Lower risk of injury

• Time consuming

• “Teasing” every other day

• Mated when in season – usually from day 3

Summary

5 day oestrus 16 day dioestrus

ovulation

oestrogen progesterone

Summary

5 day oestrus 16 day dioestrus

ovulation

Teased * * * * * * *

oestrogen progesterone

Summary

5 day oestrus 16 day dioestrus

ovulation

Teased * * * * * * *

Mated * *

oestrogen progesterone

Early Breeding

• Man imposed breeding season

• Under lights• Hormonal

manipulation

Under Lights

• 8 – 10 weeks to be effective

• 7am – 11pm – add light at end of day

• 4m x 4m box – 150W clear bulb

• Newspaper test

• Good bodily condition, housed and well fed

• Healthy, good de-worming, regular dental checks

Foal Heat

• 330 day pregnancy

• To foal yearly, needs to be back in foal by 25 days post foaling

• Mare unique – return to fertile oestrous & ovulate within two weeks

• Use this “foal heat” ??

Foal Heat

• Most mares return to heat 5 – 8 days after foaling

• Significant reduction in diameter of uterus occurs very rapidly – involution

• Delayed involution – difficult birth, abortion or retained placenta

• Foaling events VERY important• Assess involution

Foal Heat

• Accurate foaling history

• Post foaling examination 5 – 8 days

• Institute early therapy

• Complications :-1. Lower pregnancy rate ( & subsequently)

2. Lower foaling rate

Foal Heat Breeding

Do we or don’t we……………?

Factors to consider:

1. Will foal race?

2. Will foal be sold young at Sales?

Expectations

• TB mares – pregnancy rate 73%

• TB mares – foaling rate 67%

• Ponies have slightly better rates

Expectations

Mares average conception rates per cycle :

1. Natural service : 65 %

2. Fresh / chilled AI : 55 %

3. Frozen AI : 45 %

Pregnancy Rate

1. Fertility of stallion

2. Fertility of mare

3. Management of the mare at mating

Mare fertility

• Age

• Health

• Condition

• Reproductive conformation

• Previous breeding history

• Breeding Soundness Examination

BSE

• Categorises mare in attempt to determine likely breeding potential :

1. Satisfactory breeding potential

2. Questionable breeding potential

3. Unsatisfactory as a potential brood mare

BSE

• History• General physical• External genitalia• Swabs – CEM• Speculum• Internal exam

(manual)

• Internal exam (ultrasound)

********************• Further tests

1. Cervical / endometrial swabs

2. Endo biopsy

3. Endoscopy

Vulval Conformation

• Full firm vulval lips• Vertically orientated• Meet evenly in

midline• 80%+ below pelvic

brim• Anus “above” lips

Vulval Conformation

• Anus drawn forward• “shelfing” of vulval

lips• Above pelvic brim

Caslicks

• Occasionally necessary

• Prevents air / infection being “sucked” into vagina

• MUST be removed prior to foaling

Reproductive Expectations

Conc. Rate

Foaling Rate

AGE13

65%

YEARS

Pregnancy Diagnosis

Advantages :

1. Management of the mare

2. Re-breed

3. Sales / insurance

4. Stud fees ( NFNF / NFFR )

5. Twin management

Pregnancy Diagnosis

1. Ultrasound / manual palpation

2. Blood test later in gestation

3. Others available – less reliable

Ultrasound

• 2 scans• 1st scan

15 days• In foal / twins

Ultrasound

• 2nd scan

25 / 26 days

Heartbeat / twins

Ultrasound

• No risk to mare / foal• The procedure /

examination is potentially dangerous to mare & vet

Manual Palpation

• Need adequate restraint

• 42 days upwards ( problem if twins )

• Usually done October to confirm pregnancy

Blood Tests

• Small mare / fractious mare

• Inadequate facilities

• Problem if twins

1. eCG – from 45 days – false positives

2. Oestrone sulphate – from 100 days

Twins

• Double ovulation

• Undesirable – uterus cannot easily sustain

• Abortion; birth of two weak foals; birth of 1 live, 1 dead; birth of 2 dead foals at term

• Single pregnancy / monitor and return to oestrus if not naturally reduced

Twins

• Identify with early scans

• Manual reduction – before 16 days

• Takes time / patience and experience

Twins

• If mare aborts / re-absorbs after day 45, unlikely to breed that season – production of eCG.

• Monitor and react by day 32

Ultrasound Scanning

• Invaluable in breeding plan

• Not infallible

Any Questions……..?