The Estrous Cycle

Question 1

When does estrous cycle in non-pregnant mares begin?

Answer 1

when the spring transition ends

Question 2

What is the first post-partum estrus called?

Answer 2

foal heat

Question 3

When does foal heat begin?

Answer 3

7-11 days post partum

Question 4

Can you breed on foal heat?

Answer 4

yes, but not suggested because fertility is often low

Question 5

When does the 2nd post-partum estrus begin?

Answer 5

about 18-21 days after the beginning of foal heat

Question 6

The vulva, vagina, and cervix are known as:

Answer 6

the gateways to the uterus

Question 7

What is the ideal conformation of the vulva?

Answer 7

the lips should form a tight seal and be vertical

Question 8

What may change the conformation of the vulva?

Answer 8

the mares age and number of pregnancies she’s had

Question 9

Tipped vulva

Answer 9

when the vulva starts to tip to one side (become less vertical)
-will occur with more pregnancies
-happens as the back sags down and pulls the vulva

Question 10

The vulva is the _____ gateway to the reproductive tract

Answer 10

the 1st gateway

Question 11

Caslick’s procedure

Answer 11

the upper part of the vulva is staples closed either during pregnancy or before breeding
-keeps the vulva clean
-removed before foaling

Question 12

Ideal conformation of the cervix

Answer 12

must be intact and able to prevent contaminants entering uterus during pregnancy

Question 13

During estrus, the cervix is:

Answer 13

relaxed and open

Question 14

During pregnancy/diestrus, the cervix is:

Answer 14

tight and closed

Question 15

What is the function of the uterus?

Answer 15

-supports the embryo (glands in the uterus produce “uterine milk”)
-supports the fetus through interaction with the placenta (which attaches to the uterus)

Question 16

What can be done to determine uterine health?

Answer 16

-ultrasounds - to identify abnormalities
-endometrial cultures - to identify microbial status (while the mare is in estrus) and determine need for treatment/what treatment
-cytology

Question 17

Abnormalities of the uterus increase with…

Answer 17

age and number of pregnancies

Question 18

Oviduct function

Answer 18

site of fetilization

Question 19

The oviduct must be open to allow for:

Answer 19

-passage of sperm for fertilization of oocyte
-passage of oocyte and then embryo into unterus

Question 20

If a mare appears to have a normal reproductive tract but is cycling and failing to conceive what might be the issue?

Answer 20

blocked oviducts

Question 21

Ovary function

Answer 21

production of oocytes
-two ovaries, but only one is enough
-regulate hormones

Question 22

Effect of age on ovaries

Answer 22

-all oocytes are present in ovaries at birth
-oocytes are recruited from the ovary with each ovulation
-oocyte quality declines with age in mares

Question 23

The hypothalamus produces:

Answer 23

GnRH

Question 24

The anterior pituitary produces:

Answer 24

LH and FSH

Question 25

The ovary produces:

Answer 25

estrogen and progesterone -follicles produce estradiol and inhibin -corpus luteum (CL) produces progesterone

Question 26

The uterus produces:

Answer 26

PGF2alpha

Question 27

Follicle stimulating hormone (FSH)

Answer 27

stimulates follicle growth and development

Question 28

Estradiol

Answer 28

responsible for behavioral and physiological estrus (relaxing of the cervix, increased mucus production, edema in uterus, etc.)

Question 29

Inhibin

Answer 29

inhibits FSH

Question 30

Luteinizing hormone (LH)

Answer 30

stimulates ovulation and the formation of the CL

Question 31

Progesterone

Answer 31

maintains/ prepares uterus for pregnancy, suppresses estrus behavior

Question 32

Prostaglandin 2 alpha (PGF2alpha)

Answer 32

lyses the corpus luteum (CL)

Question 33

Ovarian activity during the estrous cycle:

Answer 33

-follicular wave begins -follicular deviation -preovulatory follicle -ovulation

Question 34

When does the follicular wave begin

Answer 34

day 8-12 post ovulation

Question 35

When does follicular deviation occur

Answer 35

day 14-16 -dominance phase, largest follicle 20-25 mm -growth of other follicles should stop (often doesn't though)

Question 36

When does the preovulatory phase occur

Answer 36

day 17-18 -largest follicle (preovulatory follicle) is about 30 mm; capable of responding to ovulatory stimuli

Question 37

When does ovulation occur?

Answer 37

day 19-21 (actual day of ovulation is day 0 of the next cycle)

Question 38

What is the typical size of the follicle at ovulation?

Answer 38

35 mm but could be up to 45-55 mm (in larger mares)

Question 39

Day 0 =

Answer 39

ovulation

Question 40

Day 2-6 =

Answer 40

small follicles

Question 41

Day 8-12 =

Answer 41

follicular growth

Question 42

Day 16-19 =

Answer 42

one follicle predominates and in 3-5 days ovulation occurs

Question 43

The dominant follicle produces:

Answer 43

-inhibin (which suppresses FSH - the development of the other follicles) -estradiol 17-B (responsible for behavioral estrus which allows for receptivity to stallion; responsible for physiological estrus, relaxation of cervix and edema in uterus)

Question 44

How long is the oocyte fertile for after ovulation?

Answer 44

about 18 hours -might be shorter in older mares

Question 45

If conception occurs, how long is the embryo in the oviduct?

Answer 45

about 6 days

Question 46

After fertilization what decreases?

Answer 46

estradiol and inhibin

Question 47

When will the mare go out of behavioral estrus?

Answer 47

24-48 hours after ovulation

Question 48

After ovulation the follicle becomes the:

Answer 48

corpus hemorrhagicum

Question 49

The corpus hemorrhagicum becomes the:

Answer 49

corpus luteum

Question 50

The corpus luteum (CL) produces:

Answer 50

progesterone

Question 51

Progesterone function:

Answer 51

-suppresses behavioral estrus -tightens the cervix -increases uterine tone and uterine secretions

Question 52

The embryo is mobile in the uterus until when?

Answer 52

about day 14 post-ovulation/fertilization -believed to be a signal for maternal recognition of pregnancy

Question 53

When fertilization occurs, the corpus luteum is _____

Answer 53

retained, progesterone secretions continues

Question 54

When fertilization does not occur what does the uterus release?

Answer 54

PGF2alpha about 14 days post ovulation

Question 55

If fertilization does not occur what happens to the CL?

Answer 55

it is lysed

Question 56

If fertilization does not occur what happens to progesterone?

Answer 56

it decreases

Question 57

In diestrus, what hormones are increased?

Answer 57

progesterone and FSH

Question 58

In diestrus what hormones are decreased?

Answer 58

estradiol and LH

Question 59

In estrus what hormones are increased?

Answer 59

Estradiol, LH, and FSH towards the end

Question 60

In estrus what hormones are decreased?

Answer 60

progesterone

Question 61

Hormone regulation:

Answer 61

-FSH stimulates the follicular wave -Estradiol is produced by the follicle and stimulates an increase in LH = mare enters estrus and inhibin produced by the follicle suppresses FSH -LH stimulates ovulation and formation of CL -CL produces progesterone = prepares uterus for pregnancy, if no pregnancy the uterus releases PGF2alpha that lyses CL -Decreased progesterone allows increasing concentrations of estradiol to result in next behavioral and physiological estrus and allows increase in LH

Question 62

Through day 100-120 of pregnancy what occurs with progesterone?

Answer 62

additional follicles form secondary CL which is signaled by the chorionic gonadotropin released by the endometrium

Question 63

Beginning at day 40 of pregnancy what happens with progesterone production?

Answer 63

uteroplacental tissue begins to produce progestins

Question 64

By day 120 of pregnancy what is the primary producer of progestins that maintain pregnancy?

Answer 64

the uteroplacental tissue