To understand the different parts of the estrous cycle'

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Learning Objectives
To understand the different parts of the
estrous cycle. To understand the hormonal
changes during the estrous cycle. To
understand how the estrous cycle coordinates the
events of female reproduction so it can be
successful.
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Anestrus
Female is not cycling (No expression of heat over
time)
Cow has a 21 Day Estrous Cycle Day 0 first Day
of Standing Heat
Proestrus Tertiary follicle(s) and
oocytes undergo final maturation Estrogen
levels Female starts to become receptive
- Estrogen prepares uterus and oviducts for
sperm transport and fertilization -
Estrogen initiates uterine changes for later
embryo development
Day 17-20 (Follicular Phase)
Prior to estrus, CL is undergoing regression,
progesterone levels fall below 1 ng/mL which
allows final follicular development
One dominant follicle - Graafian Stage Stimulated
to final maturation by FSH and LH
Estrogen
Smooth muscle contractions and cilia movement
Uterine glands and oviduct secretion
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ESTRUS
Picture provided by Dr. Robert P. Wettemann
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- Day of Standing heat! Day 0 of estrous cycle
Lasts 12 to 20 hours in cow
Estrus Female in heat High estrogens
cause LH surge LH surge causes ovulation
LH surge initiates corpus luteum
formation
Estrogen from the Graafian follicle stimulate
increase in GnRH which stimulates increase in LH
GnRH increases to cause a large increase in LH
(surge release) Ovulation occurs during estrus in
ewe, sow and mare but metestrus in cow
Following ovulation - LH stimulates development
of luteal cells from the granulosa and thecal
cells of the ovulated follicle wall. Theca and
granulosa cells luteinize by LH stimulation to
differentiate in luteal cells
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Day 2-4 of Estrous Cycle
Metestrus Estrogen levels have decreased
Corpus luteum is forming Progesterone
levels start to Progesterone begins
preparing the uterus for the embryo Embryo
partially develops in the oviduct and moves into
the uterus
In cow, ovulation occurs after the end of estrus
Graafian follicle has ovulated
Developing from Corpus Hemorrhagicum
Second increase in FSH occurs to stimulate
another wave of follicular development
Moves into uterus on Day 4 - 5 depending on
species
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Diestrus Maximum corpus luteum size
High progesterone levels inhibit final follicular
development, ovulation and estrus
Embryo continues to develop in the uterus
Embryo signals the uterus it is present - no CL
regression If embryo is not present -
uterus releases PGF2a to cause CL
regression If CL regresses, progesterone in
blood decreases and Graafian follicle(s)
begin final development that occurs in proestrus
for ovulation at estrus.
Day 5 - 17 of Estrous Cycle
Mature at Day 12 of estrous cycle
Inhibits final maturation of follicle and
estrus Negative feedback on GnRH
Estrous Cycle starts over!!!!
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Hormonal Profiles During the Estrous Cycle
Follicle will become atretic and regress as a
new follicle grows to ovulate with CL regression
Second Follicular Wave
ng nanogram 10-9 grams LH, FSH,
Progesterone pg picogram 10-12 grams
Estrogen, PGF2a
First Follicular Wave
When progesterone is less than 1 ng/ml it
usually means the cow has regressed the CL and
is coming into heat during the estrous cycle
Increases for CL regression
Second increase of FSH for follicle development.
Inhibin is low as is progesterone
LH surge for ovulation
Estrus
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Mare
Estrus
Estrus
Adapted from Ginther, O.J. 1992. 2nd
Edition Reproductive Biology of the Mare. p288
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Phases of the Estrous Cycle Follicular
Luteal
Phase of the female estrous cycle when she is
under estrogen stimulation Proestrus and
Estrus
Phase of the female estrous cycle when she is
under progesterone stimulation Metestrus
and Diestrus
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Species Variation in Estrous Cycle Characteristics