9. Equine Estrous Cycle, Palpation, and Pregnancy Diagnosis

How would you describe the cyclicity of the mare?

seasonal polyestrus

How long is the follicular phase (estrus) in the mare?

4-7 days

How long is the luteal phase (diestrus) in the mare?

14-15 days

Horse are long day breeders. How would you describe this in terms of when they start to cycle, anestrus, and transition? (3)

- Cycle in spring and summer

- Anestrus in winter

- Transitional in early spring and late fall

How would you describe the hormone activity during anestrus?

- Progesterone low

- Estrogen low

How would you describe the uterus during anestrus?

flaccid

How would you describe the cervix during anestrus?

in between soft and hard

Durning anestrus some mare's may tease the stallion, why do they do this?

lack of progesterone

When is the transitional period in the mare?

early spring

What are the hormones that increase during transition in the mare? (2)

FSH, LH

T/F There is no ovulation that occurs during the transitional phase

True

How would you describe the uterus durning the transition phase?

Uterus still flaccid +/- edema

Mares are (long/short) day breeders. This means that their photoperiod is (increases/decreased). When the light enters the retina, it travels to the ____ gland and causes a decrease in ____(hormone)___. This causes the hypothalamus to release _____ that works on the _____ _____ gland and releases ___(hormone)__ and ___(hormone__ that acts on _____

long, increased, pineal, meletonin, GnRH, anterior pituitary, FSH and LH, ovaries

List in order the organs/glands that are affected most by the light starting with the retina in regards to the HPG pathway.

Retina, pineal gland, hypothalamus, anterior pituitary gland, ovaires

What is the first hormone that increases durning the transition phase? Which one is second and how would you describe the amplitude?

- FSH

- LH responds later with increased amplitude

How would you describe the cycles and follicular growth durning the transition phase?

irregular cycles and slower follicular growth

she said know the chart on slide 7 so all these question are coming from that, im sorry in advance

it's okay <3

How long is estrus in the horse?

5-7 days

What hormone is high when the horse is in estrus?

estrogen

Due to the estrogen being high, what is growing on the ovary?

ovulating follice

BOOM, the follicle ovulates. What hormone starts to decrease after this?

estrogen

What makes the mare's estrus cycle different than the other animals? (she said know this)

sustained LH surge (5-7 days)

Once the follicle have ovulated. What structure is present on the ovary and what hormone is being produced?

CL, progesterone

What hormone continues to cycle regardless of pregnancy or the other hormones present?

FSH

About day 12-14, what happens that causes the CL to lyse?

if there is no fetus bouncing around in the uterus, the endometrium release PGF2a which leads to lysing of the CL and a decrease in P4

okay that was alot but now youre done

YIPPEEEEEE <3

What are the TWO hormones of Cyclicity?

Progesterone and estrogen

What is happening when there is progesterone present? (6)

- CL is present

- Diestrus

- Increase uterine tone

- Close cervix

- Decrease uterine activity

- No estrus behavior

What happens when estrogen is present in the mare? (6)

- Follicles

- Estrus

- Decrease uterine tone

- Uterine edema

- Relax cervix

- Estrus behavior

Estrus is also known as what phase?

follicular phase

What happens durning estrus and how long does it last?

growth of follicles, 5-7 days

T/F Durning estrus, the mare is receptive to the stallion

True

How will you know if the mare has ovulated?

Ovulate 1-2 days before behavioral signs stop

What structure is present durning diestrus?

Corpus Luteum

How long does diestrus last? How does the mare react durning this?

14-15 days, rejects the stallion

How many follicles ovulate per cycle?

1-2 follicles

T/F YOU MUST BE GOOD PALPATERS TO BE GOOD AT REPRODUCTION!!!!

True

What do you need to be cautious about when doing a trans rectal palpation?

rectal tears

T/F You should palpate against "tight" mucosa so it is easier

False, do not do this bc it is usually a Pneumo-rectum or Straining mares

General rules for palpation: read

Keep fingernails short

No rings, watches, etc

DO NOT try to palpate around manure

DO NOT stand directly behind mare

Always be aware of what you are doing

Safety of you AND mare first!

amazing

What is the first step you should do when palpating a mare?

Clean out manure armpit deep

Once you've cleaned out the mare, what is the order of structures that you come into contact with when palpating?

- Cervix

- Uterine body

- Uterine horn

- Ovary

- Uterine horn to other ovary

How do you grade the cervix?

Grade 1,2,3,4 (1 is the tightest and 4 is the loosest)

Where does the uterus originate from?

Paramesonephric duct

When you are palpating the uterus, what are you evaluating?

- tone

- symmetry

What structure is unique to horse due to the ovulation fossa being present? This structure is the reason why you can lavage a horses uterus

Oviductal papilla

What structure is located adjacent to the lateral surface of the ovary?

oviduct

What are the THREE parts of the oviduct in order from closest to the ovary to furthest?

Infundibulum, Ampulla, Isthmus

Where do the oviducts orginate from?

Paramesonephric origin

What are some unique features about the mare's ovary?

- inside out (the medulla is on the outside and the cortex is on the inside)

- ovulation fossa (this is where the oocyte is ovulated through)

FYI (aka just read): In regards to the ovaries:

- Length 5-8cm, Width 2-5cm, 3-5 cm Height

- Golf ball-Tennis ball

- Location: 3-5 lumbar vertebrae

- Left 2-3 cm more caudal than right

okay

What arises on the ovary that lets you know that the follicle has ovulated? What does this structure turn into a couple days after ovulation?

Corpus Hemorrhagica (CH), CL

T/F The CL is palpable in the mare

False, due to the ovary being inside out

How big does an Ovulatory follicles need to be in order for the drugs to act on them?

35mm

How will you know on ultrasound if a follicle is approaching ovulation?

- Thickening edge

- "Pointing"

What way does the ovary "point" to on ultrasound?

towards the ovulation fossa

At what day does the embryo enter the mares uterus?

day 5.5-6

The embryo remains mobile until what day? This mobility helps with what process?

Day 17, it helps with maternal recognition (basically it lets the mare know she's pregnant and not to release PGF2a and lyse the CL)

What happens to the embryo after day 17 in the uterus?

it becomes fixed (it doesnt bounce around anymore)

When does the embryo implant in the mare?

40

When will you do the first transrectal ultrasound?

day 14

When can you detect the heartbeat?

day 25

Fetal sexing occurs when?

day 60-70

When does the fetus fall over the brim of the pelvis?

5-6 months

Early pregnancy detection is important for what detrimental factor?

the presence of twins

When will you be able to tell if there are twins on ultrasound?

14 days after ovulation

At day 14 if there are twins in the uterus, what is the best next step?

Best to eliminate twin at this stage

What is it called when two follicles ovulate at approximately the same time during the same estrous cycle?

Synchronous

What is it called when two follicles ovulate at different times during the same estrous cycle?

Asynchronous

What hormone is release by the embryo while it is in the oviduct that helps with maternal recognition of pregnancy?

PGE2

What other process helps with maternal recognition of pregnancy?

Mobility of embryo

FYI (she said she wasnt gonna ask number and i trust her)

25-30 d golf ball

35-40 d tennis or

baseball

45-50 d softball

60-65 d cantaloupe

or small football

90-120 d basketball

im not gonna remember that

What happens when there is an invasion of trophoblast cells around chorionic

girdle?

Endometrial cups

What do the Endometrial cups produce that can help you know if the mare is pregnant?

Equine Chorionic Gonadotropin (eCG)

The endometrial cups stimulate the development of what that helps to maintain the primary CL?

accessory CL

When do the endometrial cups arise?

day 37-120 (day 70)

T/F Once the pregnancy has been terminated, the endometrial cups disappear in the following days

False, they remain even if the pregnancy is loss

The pregnancy relies on what structure until day 100-120 to help maintain pregnancy?

CL

After the CL loses it P4, what takes over to help maintain the pregnancy?

Feto-placental unit

What do you need to measure in order to check pregnancy viability after the CL is gone? Why?

Measure progestins because the serum P4 is low

T/F Estrogen rises, then remains stable until birth and both E2 and P4 decrease shortly before birth

True

What is the average gestation of the mare?

340 +/- 20 days (11 months)

What determines the length of gestation?

foal

What can be used to determine if a mare is pregnant durning day 19 to 25 but is not great at pregnancy diagnosis?

progesterone

What can be used as a pregnancy diagnostic during day 40-120?

eCG

What is the best pregnancy diagnostic? Why? When can you detect this hormone?

- Estrone sulfate because it is produced by the fetal gonad

- D 60