equine pregnancy Flashcards
early events of pregnancy
commences with mating/insemination and fertilization
billions of sperm ejaculated into mare uterus- few thousand to oviduct via tube-uterine junction
sperm= morphologically normal, stored in oviduct until oocyte transported from fimbrial end
day 0
sperm are deposited in repro tract concurrent with pre-ovulatory follicle
after adequate maturation, follicle ruptures and releases the oocyte
day of ovulation= 0
CL, present in both diestrus and early pregnancy in the mare, produces progesterone
endocrinology of pregnancy
early pregnancy supported by ovarian progesterone
secondary CL supply support in addition to primary (1st third of pregnancy)
later 2/3 of pregnancy supported by progestin produced by fetoplacental unit, during this part of gestation, progesterone= at baseline conc.
hormones and days
day 0= increasing progesterone
estrogen low
day 40= increasing ovarian progesterone until around day 100, ovarian estrogen follows same pattern but at lower concentration
day 160= fetoplacental estrogen increasing as ovarian progesterone falling along with estrogen
fetoplacental 5a-pregnanes start increasing
day 335- parturition= decline of progesterone and great rise in 5a
oviductal events in mare
infundibulum- covers ovulation fossa
isthmus
ampulla- sperm passage
fertilization- ampullary isthmic junction
preovulatory follicle ovulated to fimbriae then ovum transported and fertilized in ampullary-isthmic junction
embryo transport to uterus
day 5.5 to 6
enters uterine lumen
embryonic transport through oviduct facilitated by prostaglandin E from embryo which also allows for relaxation of uterotubal junction
compact morula
early embryo cleaves multiple times to form while in oviduct
contained within the zona pellucida
blastocyst
early uterine embryo developed to blastocyst stage and shed its zona pellucida
glycoprotein coating (capsule) replaces zona pellucida which is unique to the horse
Capsule
role in shape maintenance (18-20 days of pregnancy)
spherical shape= imps. for movement of embryo through uterus and maternal recognition of pregnancy
thought to protect the embryo as it moves through the uterus because highly motile
expanded blastocyst
can see inner cell mass
commonly flushed from uterus at day 7-8
unfertilized oocyte
do not produce PGE, retained in oviduct
strong indication that embryo is present if seen post flush
early detection of pregnancy
day 13-15 post ovulation
mare can ovulate multiple follicles days apart
impt. for detection of twins which is typically due to double ovulation a few days apart
twins
not well tolerated due to placentation
reduction of twins= best option because don’t get placental help needed
mobility and fixation of conceptus
equine embryo highly mobile for first 16-17 days of gestation- traverse both uterine horns and uterine body
impt. for maternal recognition of pregnancy (twins also do this)
increasing size of vesicle as well as increased uterine tone, embryo becomes fixed at base of uterine horn around day 17
early embryo nutrition
relies on yolk sac and uterine glands
yolk sac= transient, provides nutrition to embryo for ~ first 40 days
histiotrophe- produced by uterine glands, source of nutrition for the embryo until placentation develops
glands= instrumental for nutritional support
endometrial cups
day 37
result from migration of trophoblastic cells into endometrium ~36-37 days gestation
endometrial cups secrete equine chorionic gonadotropin which is like LH, impt. for early pregnancy maintenance
Equine Chorionic gonadotropin
responsible for formation of secondary CL which are essential to pregnancy maintenance
secondary CL secrete progesterone until about 100-120 days of gestation at which time the placenta fully formed
P4 high near day 0= primary CL, primary CL along with eCG increases and then along with accessory CL peak around day 100
ovarian progesterone
due to secondary CL
later 2/3 gestation fetoplacental unit produces progestins
placentation
diffuse, epitheliochorial, non-deciduate (non invasive) and microplacentomes
microcotyledons interdigitate with endometrium to provide fetal support (if compromised then premature delivery)
factors impt. for parturition
length of gestation, fetal maturation, colostrum production, cervical dilation
length of gestation
highly variable (320-360 days)
each mare has own gestational length, repeatable year after year
affected by day length and season
fetal maturation
occurs in last week of gestation
cortisol rise in last 48 hrs, premature delivery devastating because cortisol not yet secreted
adrenal reaches critical weight and begins production of fetal cortisol indicating fetal maturity and readiness for birth
fetal lamb and piglet undergo final maturational changes initiated by cortisol in weeks prior to delivery
cortisol
does not rise in equine pregnancy until last 24-48 hrs prior to delivery
premature delivery
results in neonate that is not well prepared for extrauterine life
colostrum production
multiparous mare develops mammary glands 2-4 wks prior to foaling
maiden mares can have small udder or late development
colostrum prod. critical for conferring immunity to naive equine neonate
bulk of colostrum= produced in last 48 hrs of gestation
production of milk= essential for survival
mammary secretion electrolytes
changes correlated with fetal maturity
Ca2+> 40 mg/dl
increase K+ and decrease Na+
indicator of when might foal, if considered for induced parturition values= impt. for optimizing the ability of neonate to survive outside of uterus
cervical dilation
occurs prior to parturition, faster delivery
improved neonatal adaptability
critical for delivery, if closed cervix delivery slowed and foal experiences hypoxia
hormones and cortisol
final days of pregnancy- along with rise in cortisol, rise in fetoplacental progestogen conc. and fall in estrogen which initiate parturition
opposite of sheep where progesterone decreases and estrogen increases
stages of parturition
Stage I= 1-4 hrs
II= 30-60 min
III= greater than 3 hrs
stage I
wander around stall
fetus orients self in birth canal- rearrange
stage II
30-60 minutes
ends with delivery of the fetus
stage III
placental expulsion
>3 hours considered retained
can be an emergency
