The Estrous Cycle Flashcards
When does estrous cycle in non-pregnant mares begin?
when the spring transition ends
What is the first post-partum estrus called?
foal heat
When does foal heat begin?
7-11 days post partum
Can you breed on foal heat?
yes, but not suggested because fertility is often low
When does the 2nd post-partum estrus begin?
about 18-21 days after the beginning of foal heat
The vulva, vagina, and cervix are known as:
the gateways to the uterus
What is the ideal conformation of the vulva?
the lips should form a tight seal and be vertical
What may change the conformation of the vulva?
the mares age and number of pregnancies she’s had
Tipped vulva
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
The vulva is the _____ gateway to the reproductive tract
the 1st gateway
Caslick’s procedure
the upper part of the vulva is staples closed either during pregnancy or before breeding
-keeps the vulva clean
-removed before foaling
Ideal conformation of the cervix
must be intact and able to prevent contaminants entering uterus during pregnancy
During estrus, the cervix is:
relaxed and open
During pregnancy/diestrus, the cervix is:
tight and closed
What is the function of the uterus?
-supports the embryo (glands in the uterus produce “uterine milk”)
-supports the fetus through interaction with the placenta (which attaches to the uterus)
What can be done to determine uterine health?
-ultrasounds - to identify abnormalities
-endometrial cultures - to identify microbial status (while the mare is in estrus) and determine need for treatment/what treatment
-cytology
Abnormalities of the uterus increase with…
age and number of pregnancies
Oviduct function
site of fetilization
The oviduct must be open to allow for:
-passage of sperm for fertilization of oocyte
-passage of oocyte and then embryo into unterus
If a mare appears to have a normal reproductive tract but is cycling and failing to conceive what might be the issue?
blocked oviducts
Ovary function
production of oocytes
-two ovaries, but only one is enough
-regulate hormones
Effect of age on ovaries
-all oocytes are present in ovaries at birth
-oocytes are recruited from the ovary with each ovulation
-oocyte quality declines with age in mares
The hypothalamus produces:
GnRH
The anterior pituitary produces:
LH and FSH
The ovary produces:
estrogen and progesterone
-follicles produce estradiol and inhibin
-corpus luteum (CL) produces progesterone
The uterus produces:
PGF2alpha
Follicle stimulating hormone (FSH)
stimulates follicle growth and development
Estradiol
responsible for behavioral and physiological estrus (relaxing of the cervix, increased mucus production, edema in uterus, etc.)
Inhibin
inhibits FSH
Luteinizing hormone (LH)
stimulates ovulation and the formation of the CL
Progesterone
maintains/ prepares uterus for pregnancy, suppresses estrus behavior
Prostaglandin 2 alpha (PGF2alpha)
lyses the corpus luteum (CL)
Ovarian activity during the estrous cycle:
-follicular wave begins
-follicular deviation
-preovulatory follicle
-ovulation
When does the follicular wave begin
day 8-12 post ovulation
When does follicular deviation occur
day 14-16
-dominance phase, largest follicle 20-25 mm
-growth of other follicles should stop (often doesn’t though)
When does the preovulatory phase occur
day 17-18
-largest follicle (preovulatory follicle) is about 30 mm; capable of responding to ovulatory stimuli
When does ovulation occur?
day 19-21 (actual day of ovulation is day 0 of the next cycle)
What is the typical size of the follicle at ovulation?
35 mm but could be up to 45-55 mm (in larger mares)
Day 0 =
ovulation
Day 2-6 =
small follicles
Day 8-12 =
follicular growth
Day 16-19 =
one follicle predominates and in 3-5 days ovulation occurs
The dominant follicle produces:
-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)
How long is the oocyte fertile for after ovulation?
about 18 hours
-might be shorter in older mares
If conception occurs, how long is the embryo in the oviduct?
about 6 days
After fertilization what decreases?
estradiol and inhibin
When will the mare go out of behavioral estrus?
24-48 hours after ovulation
After ovulation the follicle becomes the:
corpus hemorrhagicum
The corpus hemorrhagicum becomes the:
corpus luteum
The corpus luteum (CL) produces:
progesterone
Progesterone function:
-suppresses behavioral estrus
-tightens the cervix
-increases uterine tone and uterine secretions
The embryo is mobile in the uterus until when?
about day 14 post-ovulation/fertilization
-believed to be a signal for maternal recognition of pregnancy
When fertilization occurs, the corpus luteum is _____
retained, progesterone secretions continues
When fertilization does not occur what does the uterus release?
PGF2alpha about 14 days post ovulation
If fertilization does not occur what happens to the CL?
it is lysed
If fertilization does not occur what happens to progesterone?
it decreases
In diestrus, what hormones are increased?
progesterone and FSH
In diestrus what hormones are decreased?
estradiol and LH
In estrus what hormones are increased?
Estradiol, LH, and FSH towards the end
In estrus what hormones are decreased?
progesterone
Hormone regulation:
-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
Through day 100-120 of pregnancy what occurs with progesterone?
additional follicles form secondary CL which is signaled by the chorionic gonadotropin released by the endometrium
Beginning at day 40 of pregnancy what happens with progesterone production?
uteroplacental tissue begins to produce progestins
By day 120 of pregnancy what is the primary producer of progestins that maintain pregnancy?
the uteroplacental tissue
