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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……..?