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M.J.F COLLEGE OF VETERINARY & ANIMAL SCIENCE,CHOMU, JAIPUR (RAJ.)
DEPARTMENT OF VETERINARY GYNAECOLOGY & OBSTETRICS
ESTROUSCYCLE
Presented by: Dr. ROHIT JUNEJA
(MVSc)
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DEFINITIONS:
ESTROUS CYCLE:• Derived from Latin word oestrous (frenzy) and originally
from Greek (gadfly)
Estrous cycle comprises the recurring physiologic changes
that are induced by reproductive hormones in
most mammalian females.
Period from one estrus to the next.
Two phases:
Follicular Phase (proestrus and estrus)
Luteal phase(metestrus, diestrus )
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DEFINITIONS :
ESTRUS: Period of sexual receptivity.
• Commonly referred to as “Heat”
ANESTRUS: Period when female does not
showed estrous cycles
• Occurs during pregnancy etc.
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• Cycle is categorized by frequency occurrencethroughout the year:
– Polyestrus: exhibit regular estrous cycles throughout
the year
• Example: Cattle, Swine, Rodents
TYPES OF ESTROUS CYCLE
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• Seasonally polyestrus:
– Cycles occur only during certain times of the year/ exhibit estrous
cycle during a particular season
• Long-day breeders:
– Cycle when day length increases
Example: Mare
• Short-day breeders:
– Begin to cycle as day length decreases
»Example: “ Sheep, Goats “
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• Monoestrus:
– One cycle per year
• Periods of estrus last for several days
– Example: Dogs, Wolves, Foxes, Bears,
wild animal, Elephant, Tiger.
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PHASES OF ESTROUS CYCLE
• FOLLICULAR PHASE:
– Short phase - only 20% of cycle
– Period from regression of corpus luteum to
ovulation
– Preovulatory follicle
– Dominant hormone is estradiol
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PHASES OF ESTROUS CYCLE
• LUTEAL PHASE:
– Long phase - 80% of cycle
– Period from ovulation to corpus luteum regression
– Corpora lutea
– Dominant hormone is progesterone
– Follicle continue to grow and regress during this
phase
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STAGES OF ESTROUS CYCLE
• Four stages:
– Proestrus
– Estrus
– Metestrus
– Diestrus
• Follicular phase = Proestrus + Estrus
• Luteal phase = Metestrus + Diestrus
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PROESTRUS
• Begins when progesterone
declines(luteolysis) and ends at onset of estrus
• Lasts 2 to 5 days
• Period of major endocrine transition
– Progesterone dominance to estrogen dominance
– FSH and LH responsible
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“Building Up”
– Ovarian follicle, with enclosed ovum, increase in size
– Estrogens absorbed from the follicles into
blood stream stimulate increased vascularity
and cell growth of tubular genitalia, in
preparation for estrus and pregnancy
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• Period of sexual receptivity
• Large increase in estrogen
– stimulates release of LHRH
• FSH decreases due to estrogen and inhibin
– During or shortly after estrus, ovulation
occurs due to major surge in LH
– LH levels increase due to LHRH
– Estrus stops once ovulation occurs.
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• Corpus Luteum predominant
• ↑Increase in progesterone, ↆ decrease in estrogen
• Endometrial lining thickens and uterine
muscles show increased development.
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• Relatively short period of time between
estrous cycles during the breeding season
of polyestrous animals
– No reproductive activity
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• CL is fully functional*
• High levels of progesterone
• End with luteolysis
• 10 to 14 days (Depending on the species of animal)
*corpora lutea
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• Proestrus= Formation of ovulatory follicle + E2 secretion
• Estrus = Sexual recepitivity + peak E2secretion
• Metestrus = CL formation + beginning of P4 secretion
• Diestrus = Sustained luteal secretion of P4
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• Long period of inactivity between sexual seasons
– No regular estrous cycles
– Ovaries relatively inactive
• No follicles or CL
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Average Reproductive Cycles
Species Length of
Estrous Cycle
Length of
Estrus
Ovulation Length of
Pregnancy
Cow 21 days 18 hr 11 hr after 282 dayspolyestrus end estrus
Ewe 17 days 29 hr near end 148 daysseasonal (fall) estrus
Sow 21 days 48-72 hr 35-45 hr 115 dayspolyestrus after start
estrus
Mare 21 days 4-8 days 3-6 day of 335 days seasonal (spring) estrus
polyestrus (1-2 days
before end of estrus)
The basic pattern of the estrous cycle is the same in all domestic animals, but
some specific differences are found in specific parts of the cycle. Some
specifics about relevant farm species are summarized in Table
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ChChararacteacteririsstiticscsofofCharacteristics of Estrous Cycles
Cow Ewe Sow Mare
Estrous cycle (days) 21 17 21 21
Proestrus (days) 3-4 2-3 3-4 3-4
Estrus 12-18 hr 24-36 hr 48-72 hr 4-8 days
Metestrus (days) 3-5 3-5 3-4 3-5
Diestrus (days) 10-14 7-10 9-13 6-10
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Variation in Cycle Types
Example Type of Cycle
Follicular Development
Ovulation & CL Formation
CLFunction
Cow, ewe, Long Spontaneous Spontaneous Spontaneous sow, mare
Rats, mice, Short Spontaneous Spontaneous Induced hamsters (4 days) (prolactin)
Rabbit, cat, Induced Spontaneous Induced Induced mink, ferret, (LH surge)otter, alpaca
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Methods of Estrus Detection
Causes of Anestrus
Tail-painting & use of chalk
Use of closed circuit
television female activity
changes Progesterone testsVaginal probes
Use of teaser
animals Chin-male
devices Heat-
mount detectors
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CL CL
Ovulation Atresia
ProgesteroneCA
EstradiolPGF2
FSH
LH
-7 - 6 - 5 - 4 - 3 - 2 -1 0 1 2 3 4 5 6 7 8Days Relative to the Gonadotropin Surge
Diestrus Proestrus Estrus Metestrus Diestrus
1
The estrous cycle
may be divided into
several phases based
on behaviour changes
or structural changes
in internal & external
genitalia.
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Atresia
CL
CA
Ovulation
CL
Days Relative to the Gonadotropin Surge0 1 2 3 4 5 6 7 8-7 - 6 - 5 - 4 - 3 - 2 -1
FSH
LH
PGF2
Estradiol
Progesterone
Metestrus DiestrusProestrusDiestrus Estrus
Follicular Phase
Proestrus
• Follicle enlarges
• Estrogen increases
• Vascularity of the female reproductive tract increases
• Endometrial glands begin to grow
• Estrogen levels peak
2
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Estrus
•
•
•
•
•
•
•
Allows male to mount
Estrogen decreases
LH surge occurs
Ovulation 24-48 h after surge of LH
Uterine motility high with contractions moving toward oviduct
Sperm transport is optimal
Cervical mucus volume increases
Follicular Phase3
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Atresia
CL
CA
Ovulation
CL
Days Relative to the Gonadotropin Surge4 5 6 7 8
LH
-7 - 6 - 5 - 4 - 3 - 2 -1 0 1 2 3
FSH
PGF2
Estradiol
Progesterone
Metestrus DiestrusProestrusDiestrus Estrus
Luteal PhaseLuteal Phase
Metestrus
• Estrogen low
• Ovulation in cow
• Corpus hemorrhagicum present
• Uterus
Contractions subside
Endometrial glands continue to grow and become coiled
In cattle bleeding occurs
• FSH increases
Triggering growth of follicles
4
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Atresia
CL
CA
Ovulation
CL
LH
-7 - 6 - 5 - 4 - 3 - 2 -1 0 1 2 3 4 5 6 7 8Days Relative to the Gonadotropin Surge
FSH
PGF2
Estradiol
Progesterone
Metestrus DiestrusProestrusDiestrus Estrus
Luteal PhaseLuteal Phase
Diestrus
• Progesterone high
• FSH
Increases at some point to cause growth of ovulatory follicle
• Uterus
Secrets fluid but volume gradually decreases
Contraction stop
CL regresses at the end of this period if female is not pregnant due to PGF release
5
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Before heat
(6-10 h)
Hours 0 6
Hours from the start of estrus
9 18 24 28
Egg released
Life of egg
(6-10 h)
Standing heat
(18 h)After heat
(10 h)
Estrus in cow and associated featured
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Approximate Values for Selected Reproductive Events in Female
Domesticated Mammals
SpeciesLength of
cycle (days)
Duration of estrus (hours) Approximate time of ovulation Normal breeding season
CowMean=20.5
Range 17 - 23Mean < 10
Range 1 - 2430 h after beginning of estrus All year
BuffaloMean=21
Range 18 - 22Mean < 15
Range 4 - 2432 h after beginning of estrus All year
Mare
Mean=21 Range 12 - 35
Mean=120 Range 24 - 240
Near end of estrus Spring & summer
Ewe
Mean=16 Range 12 - 19
Mean=30 Range 20 -48
26 h after beginning of estrus Fall (variable with breed)
DoeMean=20
Range 16 - 22Mean=40
Range 24 - 72On 2nd day of estrus Fall
Sow
Mean=20 Range 16 - 22
Mean=48 Range 24 - 90
36 h after beginning of estrus All year
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