length of equine gestation
variable
avg: 335 to 342 (11 months)
viable foals delivered from 315 to 400 days
placentitis or anything that stresses baby will cause premature birth
any mare showing signs of premature parturition or prolonged gestation should be examined
physiologic factors affecting gestation length
season of breeding/birth (summer shorter)
mares under light
increased nutrition
older mares have increased incidence of both long and short gestation
sex of fetus-colts longer
sire
pathologic factors affecting gestation length
short: twins, placentitis, other abortigenic infections
long: fescue toxicity
either: endometrosis (degenerative/fibrotic endometrium)
When is the fetus ready to be birth?
due to activation of the fetal hypothalamus-pituitary-adrenal axis
increased cortisol secretion leads to lung maturation, gut maturation, hepatic glycogen stores, thermoregulate, CNS (stand & move), initiate suckling
when is the fetal HPA axis activated in horses?
last 1-2% of gestation (last 3 to 5 days)
how should you prepare for foaling?
move to foaling location 4-6 weeks prior to expected due date
exposure to local organisms to develop abs (colostrum)
vaccinate-colostrum
closer observation
predict a foal
measures Ca and Mg
5 indicator squares
more squares changing color
more specific for when she won't give birth
milk electrolyte monitoring
total score of >35 suggests birth within 24 hours
take sample in evening
calcium, sodium, potassium
a low score is a better predictor that the mare won't foal than a high score is that she will foal
less useful in sick mares or those with placentitis
when do mares like to foal?
8 pm to 6 am
mammary secretion pH
<6.4
when the mare goes under 6.4
foal alert
suture to vulva lips 1-2 weeks before due date
lips part at birth pulling out magnet
alarm signalled
false alarms
final prep
make sure foaling area clean
wrap tail to keep it out of the way
wash perineum and udder
reduce incidence of neonatal infections
positions occupied by the fetus in the last month of gestion
2/3 dorsal recumbency
1/3 left or right lateral
parturition in mare: stage 1
uterine contractions stimulate fetal movement which help put foal in birth position
cervix softens and dilates as chorioallantois and foal wedge into it
ends with rupture of chorioallantois
1 to 6 hours
between stage 1 to 2
1-5 minute window of opportunity immediately after the water breaks and before she is ready to strain to check the foal's positioning and easily correct some malpostures
stage 2 of parturition
about 20 minutes up to 60 minutes
fetus encased in amnion distends cervix and vagina intiating strong uterine and abdominal contractions
amnion visible in 10 mis after water breaks
one foot in advance of other, soles directed down
nose dorsal to legs at level of metacarpus
stage 3 parturition
delivery of fetal membranes (30 min to 3 hrs)
induction of parturition in mares
risky due to uncertain stage of maturation of foal
don't do it unless: very pressing reason
make sure foal is mature enough
criteria for induction
330+ days of gestation
relaxed ligaments
colostrum in udder
milk electrolye changes indicate maturity
relaxed cervix
corticosteroid induction
don't work well-require high dose for several days
risk of dystocia due to malposition/posture
retained placentitis
risk of side effects to mares (laminitis)
prostaglandin induction
takes up to 6 hours
not best
produce powerful contractions, could lead to complications
oxytocin induction
most widely used and method of choice
wide range of doses and routes of administration
best is low dose given IV or IM
once this starts the process it will continue on its own
mare foals within an hour of injection
premature placental separation is fairly common
will work on any mare over 300 days gestation
1st stage prolonged if cervix is not relaxed when inject, could lead to hypoxic foal
dystocia
1st or 2nd labor is prolonged or porgress is not being made
failure of amnion and/or fetal parts to appear at vulva in timely manner after rupture of chorioallantois
only 1 hoof appears
hooves are upside down
only nose appears
hooves and nose in wrong relative positions
goals for dystocia
live viable foal that isn't in ICU
live healthy reproductively sound mare
causes of dystocia
abnormal disposition
presentation
under 40 minutes of stage 2
10% morbidity/mortality
over 40 minutes of stage 2
high morbidity/mortality
After ______________ minutes of stage II labor, every _________ minutes increase in duration
30 minutes
10 minutes
leads to 10% greater risk that fetus will be dead at delivery
16% greater risk that fetus will not survive to discharge from hospital
what happens when the placenta detaches during stage 2 of labor?
foal can become asphixiated
milder cases: hypoxic-ischemic encephalopathy
if mare is not actively straining the placenta may stay attached longer. why?
foal is not engaged in pelvis (transverse/breech maldispositions)
if less assistance has been tried
breed differences: Friesian mares may have slower placental detachment
prevalence of equine dystocia
generally considered<1-4%
higher in maiden mares
some breed dependence (higher in draft horses and minis)
what kinds of dystocia will you see?
malposture of extremities (41%)
normal position and posture but large foal or weak contractions (31%)
malposition-dorsopubic (22%)
hiplock (1%)
redbag (2%)
if head becomes retained, what's the chance of survival?
25%
initial assessment of mare in dystocia
assess general health (ie attitude, MM color, CRT, shock, hemorrhage, dehydration)
perineal area (condition, protrusions, d/c, stinky?, prolapses)
vaginal exam: wrap tail and wash perineum, wash arm, lots of lube
How to tell if the foal is alive?
anterior presentation-movement, pinch coronary band, slight eyeball pressure, finger in mouth-suck, heartbeat if reach thorax
posterior presentation-pinch coronary band, anal reflex, umbilical vessel pulse
elbow lock (incomplete elbow extension)
muzzle at same level as hoof-fetlock
hand on chest and repel while applying traction on leg to extend elbow
deliver keeping one hoof in advance of other to minimize cross sectional size of foal
Hurdlers and dog sitters
uni (hurdler) or bi (dogsitter) lateral hip flexion with fetus in anterior presentation
dx: carefully feel under, beside and above fetus back to mare's pelvic inlet
tx: risk of rupturing uterus, anesthetized mare, hoist butt in air and try to repel or fetotomy
fetal oversize
if mild, lots of lube and gentle traction
if doesn't work, C-section, partial fetotomy
foot nape posture
head and front legs in vagina but one or both legs over top of head
risk of rectovaginal fistula or 3rd degree perineal laceration
tx: repel into uterus to get room, correct posture
poll posture
no nose appears following feet, feet may not come out beyond fetlocks
can palpate poll but nose is below pelvi brim
tx: repel fetus and reposition head (rotate in lateral arc then straighten, make sure neck is fully extended before applying traction)
nape posture
extreme version of poll posture
head & neck are ventrally displaced between the forelimbs
hard to reach
tx: fetotomy, C-section, anesthesize mare and hoist butt
lateral reflection of head & neck
head and neck reflected alongside thorax
often hard to reach far enough to correct
tx: try repelling body and placing snare on heaed to reposition, put one leg into carpal flexion, fetotomy
carpal flexion
unilateral or bilateral
affected carpus usually at pelvic inlet
tx: repel body, grab near fetlock and rotate limb so carpus goes dorsolaterally and flexed fetlock goes medially and limb is extended innto vagina, C-section, fetotomy
Shoulder flexion
uni-swimmer, bilateral-diver
tx: immediate C-section for live foal
manual correction: turn into carpal flexion & correct from there
fetotomy
posterior presentations
hock flexion (25% of posterior dystocias, 90% are bilateral)
hip flexion (50% of posterior dystocias, 94% bilateral)
chance of live foal remote-compression or rupture of umbilical cord leads to asphixia
hock flexion
usually bilateral
tx: repositioning is dangerous (risk of rupturing uterus), C-section, fetotomy
breech
reach in and feel a tail
tx: mutation as dangerous as hock flexio
fetotomy
transverse presentations
ventral more common (all legs presenting), ddx: twins, can sometimes mutate, C-section
Dorsal: C section, fetotomy (hard)
hydrocephalus
large domed skull-often soft
prevents passage of head or its entry into birth canal
not uncommon in ponies and mini horses
tx: ince with palm knife to collapse, remove top of skull by fetotomy
fetotomy in mares
total fetotomy rarely performed (damage to repro tract)
usually do 1-2 well planned cuts
make all cuts inside uterus, not in cervix or vagina
do not use on a mare in bad condition, do C--section
C-section in mares
not usually done in field
general anesthesia (ventral midline incision)
best option for many: transverse, breech, oversize, dogsitter
$$$
treating a mare post dystocia
check uterus for tears
ensure all placenta is passed
check for lacerations/abrasions in cervix and vagina, tx SID with abx/steroid creams to avoid adhesion formation
nasogastric intubation and give mineral oil
