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Parturition in the Mare
Veterinary Medicine

Additional Veterinary Medicine Flashcards




Gestation length in a horse


Average 342 days (range 321-385 days), note the wide variability this is not reliable for predicting parturition. Do not induce parturition in the mare! Even if the mare has ‘gone over’ her expected due date the foal is almost certainly not viable until normal parturition is ready to take place (unlike other species). Monitoring of parturition is advisable as whilst very few foaling’s have complications if they do they rapidly become an emergency and the likelihood of producing a live mare and foal is poor. 



Signs of impending parturition: 



1. Enlarged abdomen
2. Mammary development - 3 to 6 weeks prepartum. Major changes within 2 weeks of term. Initially straw-coloured discharge.
Udder distends with colostrum 2-3 days prepartum
Teat waxing last up to 48 hours.
Increase in calcium and magnesium content of milk.
At term calcium >10 mmol/l.
3. Relaxation of sacrosciatic ligaments over last few weeks and vulva in last few hours
4. Relaxation of cervix (may occur 0 to 30 days prepartum)
5. Foaling aids 

Foaling aids


Measurement of milk calcium can be useful
- Mares mare wear a monitoring alert (similar to an anti cast roller) that sets off an alarm when the mare is recumbent for prolonged periods. This can result in false alarms (if a mare lies down to sleep) and miss foalings (if the mare foals standing up, which is not uncommon)
- Some people have cameras in the stable that can be programmed into a TV in the house or even an iPhone.
- Foalert© is a small magnetic device that is sutured to the vulva
when parturition begins the magnet is opened and sets off an alarm that rings a mobile phone. This is usually very effective but in the case of a dystocia, especially a breech, the vulva lips are not parted and so the alarm fails to go off.

Mares vary tremendously in the signs that they show ranging from none to all.

NB Remember to open vulva at least 2 weeks before expected foaling date if Caslick sutures are present

Foals are highly mobile within the uterus during the first half of gestation. During the last half of gestation the foetus is in the dorso-pubic position with the head and forelimbs flexed. 



Stage I parturition : Lasts approximately 2-4 h



(mares have a high degree of maternal control over length of stage I) Uterine contractions start
Cervix relaxes and dilates
Colicky signs
Patchy sweating

In some mares delivery of the foal may be delayed for several hours or days. The end of 1st stage labour is marked by rupture of the allantochorion at an avascular area, the cervical star, and release of straw-coloured watery allantoic fluid. The foal rotates to a dorso-sacral position just before birth. The amnion should protrude through the vulvar lips within 5 min of rupture of the allantochorion. 

Stage II: lasts less than 30 mins


Assume lateral recumbency
Abdominal contractions
Foal is delivered covered by amnion (more correctly termed the allantoamnion)
The equine placenta separates from the endometrium rapidly and foetuses not delivered within a relatively short time of onset of 2nd stage labour are deprived of oxygen.
Prolonged 2nd stage labour is an emergency!
Normal presentation is anterior, dorso-sacral, extended
Do not cut the umbilical cord; you may allow excessive bleeding
NB If the red allantochorion appears at the vulvar lips, rupture the membrane and pull out the foal immediately. Differentiate from prolapsed bladder! 



Stage III: 



Expulsion of placental membranes usually occurs within 1 hour with the allantochorion turned inside out. NB Always examine placenta for completeness. 






The incidence of dystocia in horses is low (~4%), however it represents a life-threatening situation to the foal and the future reproductive performance of the mare is often reduced. Young and old mares are most commonly affected. Dystocia exists when 1st or 2nd stage labour is prolonged or not progressive and should always be considered an emergency. If no progress occurs within 10 min of onset of straining, a veterinary examination is needed. The foal will need to be delivered within an hour. Dystocia is most often caused by abnormal presentation with long foetal extremities predisposing the mare to problems with delivery. Examination of the birth canal and foetus is necessary to determine the cause of the dystocia. The foetus is particularly at risk from placental detachment, hypoxia and damage to the respiratory centre. 



Examination of the mare: 



1. Adequate restraint (not stocks) ± chemical restraint. An epidural may be administered to prevent straining. A stomach tube may be passed to prevent closure of the glottis, and straining. Uterine muscle can be relaxed by administration of clenbuterol.
2. Hygiene - bandage tail, scrub perineal region with povidone-iodine.

3. Lubrication
Assess birth canal for evidence of previous trauma, size and degree of relaxation. Check presentation of foetus and determine viability. 



Causes of Dystocia: 



1. Primary uterine inertia - usually due to voluntary suppression of foaling caused by disturbance. Cervix is partially open. Chorioallantois intact. Leave the mare alone for 20 mins. Mare can have dilated cervix for 12 hours and foal normally. Important to remember that progress needs to be quick when mare on STAGE II. Can induce parturition. See below.

2. Secondary uterine inertia - usually caused by foetal malpresentation. 3. Failure of abdominal expulsive effort.
4. Obstruction of the birth canal.
Fetopelvic disproportion is rarely a problem in mares. 

Infectious abortion


1. Equine Viral Rhinopneumonitis (Equine Herpes Virus I; EHV-1 or uncommonly EHV-4 ).
Leading infectious cause of abortion in mares in UK. Virus transmitted via the respiratory tract. Repeated exposure leaves horses immune to respiratory disease but susceptible to reinfection causing abortion. Usually occurs between 5 months of gestation and term.
Usually only a few infected mares in a herd abort.
Abortion occurs 1-4 months after infection.
Fresh foetuses expelled often within placental membranes.
Foals affected near term are viraemic, weak and die shortly after birth.
TREAT ALL ABORTIONS AS POSSIBLE EHV ABORTION. Refer pathology notes for diagnosis.

Prevention: Pregnant mares should be kept separate from other horses.

Vaccinate at 3, 5, 7 and 9 months gestation with Pneumabort K or Duvaxyn EHV 1.4. 

Equine viral arteritis - Togavirus


Causes severe systemic illness in dam which may be followed by abortion 7-10 days later (from 3 months to late pregnancy). Typically presents with fever, lethargy and depression, conjunctivitis, nasal discharge, urticarial rashes, oedema. Infection is via the respiratory or venereal route. Virus localises in accessory sex glands. 30% of infected stallions continue to shed virus after resolution of clinical signs.

Shedding stallions play a major role in disease transmission. Shedder stallions are always seropositive but not all seropositive stallions are shedders. Mares do not become carriers but 90% of mares become infected after breeding with a shedder stallion. Seropositive mares with a stable or declining antibody titre are thought not to infect stallions or in-contact animals.

Prevention: Vaccine available. 

Abortion: Bacterial


Responsible for approximately 30% of aborted foetuses seen at PM Diagnosis: Isolation from foetus and placenta. 

Abortion: fungal


Foetus is usually small and emaciated. However near-term premature foals with mycotic placentitis have a good chance of surviving.

Grossly the placenta and foetus are similar in appearance to bacterial causes of abortion although microscopically there are abundant fungal hyphae. Apsergillus is the most frequently encountered fungus. 


Non infectious abortion




Responsible for 6% of abortions. Double ovulations occur at around 16% oestrous periods. Incidence at 40 days is 1-2% of which:

65% result in abortion

21% result in birth of 1 foal
14% result in birth of 2 foals (only 14% survive to 2 weeks of age) 


Twins are dizygotic and rarely freemartins (placental fusion occurs after sex differentiation).
Abortion due to twinning especially prevalent between 8-10 months gestation.
May abort without warning but may start lactating during mid to late gestation suggesting impending abortion.
Foetal loss is due to placental insufficiency - areas of placenta-placenta contact are avillous.
Mares should be checked for twin pregnancy before day 30 and one of the conceptuses should be crushed.
Foetal stress causes initiation of birthing process. 






Associated with endometrial fibrosis/ endometrial scarring in older mares. Pregnancies confined to the uterine body also cause abortion due to decreased placentation into the uterine horns. Lack of nutrition to foal causes foetal stress/hypoxia starts birthing process. 






such as torsion account for around 40 per cent of abortions. Cords >80cm are thought to potentially cause problems. Thought to be the most common cause of abortion in the mare. 



Uterine involution: 



Occurs by 6-10 days postpartum
Little tissue is lost at parturition, therefore vaginal discharge is scant. Excessive discharge may be a sign of uterine infection. 



Foal heat: 



First oestrus occurs 7-9 days after foaling
Fertility can be lower than at subsequent heats, but many farms cover mares at this time with good results. 



Severe Pain related to Uterine Contractions: 



Most common in primiparous mares. Pain tends to be intermittent. Moderate elevation in heart rate. Sweating. Administer analgesics. Palpate uterus.
Usually subsides within 1-2 hours. 



Retained Placenta: 



This is an equine emergency.
Treatment should be initiated if the placenta is retained more than 3 hours. (2-10% of mares). Mares are likely to be less fertile at foal heat. Use 10-20 IU oxytocin IV or IM every 15 min
or 60 IU in 1 litre saline over a 1 h period
Repeat as necessary (usually expelled within 30 min)
If retention is
prolonged (>8 hours) beware of sequelae:

laminitis and endometritis.

Use more aggressive therapy:


Broad-spectrum antibiotics

The allantochorionic space may be infused with 10-12 litres dilute Povidone- iodine solution or saline. The opening in the foetal membranes is tied shut. The distension of the reproductive tract stimulates uterine contractions (via oxytocin release) and the membranes are usually passed within 30 min. 




Uterine Artery Rupture: 



Mares may exsanguinate. Survival depends upon whether haemorrhage is contained within the broad ligament or whether the ligament ruptures.
Signs of colic with weak rapid pulse and pale membranes. Keep mare in dark, quiet stable Tranquillisers may help. Do not give oxytocin. 



Rectovaginal Fistula/Perineal Laceration: 



Caused by damage to birth canal by foal's hoof /head etc.
Repair surgically after 30 days when damaged tissue has sloughed and swelling has resolved.

Three types of perineal tear:
Type 1
mucosal damage only
Type 2
damage into perineal body
Type 3
tear extends into anus, producing a cloaca 

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