1.4.1 Clinical Physiology of Pregnancy

Question 1

summary of early development in the bovine: what does the embryo do once it enters uterus? what hormone does it produce? when does it fill the horn?

Answer 1

-embyo enters uterus from oviduct
>begins elongating
>produced INF tau - signal for maternal recognition of pregnancy in cows
>fills horn by day 24 (same side as CL)
>eventually fills entire unterus

Question 2

what does the horse embryo have from day 7 - 22 that is unique among dometic farm animals?

Answer 2

capsule – The capsule is a glycoprotein layer surrounding the embryo and is critical for pregnancy to continue

Question 3

what shape is the equine embryo (vs bovine?)

Answer 3

equine: sphere
bovine: elongated

Question 4

what is the Phase of Early Mobility for the equine pregnancy? what is it essential for? how long does it last? what do we see wherever embryo is located? what happens if this process is disrupted?

Answer 4

– Essential for maternal recognition
– Embryonic signal is not known
– Mobility phase from entry into uterus until Fixation at 16 days
– Increased uterine contractions wherever embryo is located
– Embryo traverses entire uterus multiple times per day!!
– Anything that disrupts this results in pregnancy failure

Question 5

when does the equine embryo settle in place? where? coincides with what for uterus and embryo?

Answer 5

-Embryo stops moving and settles in place at the base of one horn
* Fixation ‐ occurs at day 16
* Coincides with increase in uterine tone, rapid increase in diameter of embryo and changes in the capsule making the embryo sticky

-Fixation should occur at the base of a horn
– Need NOT be the side of ovulation

• Then embryo orientation occurs with embryo proper at base of vesicle

Question 6

after maternal recognition what maintains pregnancy in the various species? what is its source?

Answer 6

• Progesterone is the pregnancy hormone – Reduces myometrial contractions
  – Exception is the equine (of course!)
• The SOURCE of progesterone varies by species and stage of gestation
• Some species keep the Corpus Luteum throughout pregnancy, some do not (need to know this! – this is important when determining how to terminate pregnancy)

Question 7

bovine gestation length

Answer 7

280d

Question 8

ovine gestation length

Answer 8

150d

Question 9

goat gestation length

Answer 9

146d

Question 10

sow gestation length

Answer 10

112d

Question 11

bitch gestation length

Answer 11

63d

Question 12

mare gestation length

Answer 12

341d

Question 13

what does progesterone do?

Answer 13

Progesterone is the pregnancy hormone – Reduces myometrial contractions
– Exception is the equine (of course!)

Question 14

Bovine:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 14

gestation: 280d

progesterone source:
CL - throughout
placenta - 150-250d

Question 15

Ovine:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 15

gestation: 150d

progesterone source:
CL - <50-60d
placenta - >50-60d

Question 16

Goat:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 16

gestation: 146d

progesterone source:
CL - throughout
placenta - 8-10% of P4

Question 17

Sow:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 17

gestation: 112d

progesterone source:
CL - throughout
placenta - no contribution

Question 18

Bitch:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 18

gestation: 63d

progesterone source:
CL - throughout
placenta - ?

Question 19

Mare:
Gestational Length and Source of Progesterone for Maintenance of Pregnancy

Answer 19

gestation: 341d

progesterone source:
CL - 120d *2nd degree CLs (cups)
placenta - >70d (estrogens, 5alpha pregnanes)

Question 20

progesterone vs estrogen in the bovine pregnancy over time

Answer 20

progesterone relatively high level and contant throughout, dips to 0 at end while estrogen low throughout, grows to peak at end

Question 21

how do progesterone and estrogen levels in the mare vs bovine differ during pregnancy?

Answer 21

• High levels of estrogen in mare throughout
• Low levels of progesterone after 150 days until close to term for mare

Question 22

significance of Endometrial cups in the mare
- when do they form, what are they made of, what do they produce?

Answer 22

• Cups begin to form about day 35
• Specialized fetal trophoblast cells that invade the maternal endometrium
• Produce Equine Chorionic Gonadotropin
• eCG is detectable from day 35 thru 120

Question 23

when is eCG detectable in the mare during pregnancy?

Answer 23

day 35 thru 120

Question 24

what does eCG do?

Answer 24

eCG has LH activity in horse
> Results in Secondary CL’s on ovaries
> which make Progesterone to maintain pregnancy thru day 120
– (remember eCG has FSH activity in ruminants for breeding management programs)

Question 25

description of the pregnancy hormone profile in the mare

Answer 25

-progesterone grows and peaks at about day 120 -eCG increases around day 35, peaks, and then decreases, stopping at day 120 -progesterone basically drops to 0 at day 150, only to increase again just before parturition -estrogen increases at day a50, as do total progestagens which keep increasing until parturition

Question 26

when do the endometrial cups die off?

Answer 26

* Have a pre‐programmed lifespan * Die off (or are destroyed?) about day 100‐120

Question 27

what happens if the fetus dies while endometrial cups are present?

Answer 27

– they remain, and continue to produce eCG – This means the mare will not come back into heat until the cups regress

Question 28

how is pregnancy maintained in the mare if progesterone is low?

Answer 28

– the placenta is starting to “make stuff” (progestagens) by day 70 and by 120 days is the primary source of pregnancy hormones

Question 29

The rise in estrogens coincides with what during mare prgnancy?

Answer 29

a dramatic increase in the size of fetal gonads, due to eCG from the endometrial cups

Question 30

what is the case for fetal vs mare gonads between day 150-220?

Answer 30

fetal gonads are bigger than mares!

Question 31

fetal gonads during mare pregnancy pump out what? what do these chemicals do?

Answer 31

Fetal gonads pump out a steroid hormone precursor, DHEA (dihydroepiandrosterone) which is converted by the placenta to various estrogens (some are specific to the horse – eg. Equilin, and Equilenin) – These are essential for normal fetal growth and development, normal myometrial contractions during labour and normal mammary gland development – But – estrogens are not “required” for maintenance of the pregnancy

Question 32

what is responsible for the maintenance of pregnancy after the endometrial cups are gone at 120 days?

Answer 32

Fetal adrenal gland produces other progestagens of pregnancy in the mare (mostly 5 alpha pregnanes such as 5 α DHP and pregnenolone) – These are biologically active in horses and appear to be responsible for the “progesterone block” of pregnancy – Bind to equine progesterone receptor