Reproductive Cyclicity

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Reproductive Cyclicity

• Repeated Opportunities to Become Pregnant

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Definitions
Estrus - noun
Period of time when the female is receptive to
the male Usually lasts for a few hours up to a
few days
Also called heat or season
Estrous - adjective
Estrous Cycle Period of time from one estrus to
the next estrus Repeated opportunities for the
female to become pregnant during a breeding
season Usually several days or a few weeks in
length
Anestrus period of time when the female is not
cycling
Menstrual Cycle Period of time from the
beginning of one menses to the beginning of
the next menses - humans and some nonhuman
primates
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Types of Estrous Cycles
Polyestrus
Repeated estrous cycles at specific intervals
throughout the year if not pregnant
Seasonal Polyestrus
Repeated estrous cycles during specific seasons
of the year
Long day breeders Short day breeders
Monoestrus
One estrus per year
Domestic canids may actually show estrus 2 or 3
times
Induced Ovulators
Ovulate in response to vaginal stimulation Cat,
Rabbit
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Brain Hypothalamus - Pituitary Gland
PINEAL
Melatonin
HYPOTHALAMUS
GnRH (Gonadotropin Releasing Hormone)
ANTERIOR PITUITARY
LH (Luteinizing Hormone) FSH (Follicle
Stimulating Hormone) PROLACTIN TSH (Thyroid
Stimulating Hormone) ACTH (Adrenal Cortical
Tropic Hormone) STH or GH (SOMATOTROPIN)
POSTERIOR PITUITARY
OXYTOCIN ADH (Antidiuretic Hormone)
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Anestrus
Gestational Anestrus
GnRH is inhibited by progesterone
Seasonal Anestrus - increase dark increase
Melatonin
Short Day Breeders GnRH is stimulated by
Melatonin from the Pineal
Long Day Breeders GnRH is inhibited by
Melatonin from the Pineal
Lactational Anestrus
Does not occur in the mare and the alpaca
Delayed by greater than 2 suckling sessions per
day
also influenced by visual, auditory, and
olfactory stimulus by own calf
Effect of lactation may be reduced with extended
time post partum
Can be confounded by post partum uterine
involution
Anestrus due to negative energy balance
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Brain Hypothalamus - Pituitary Gland
PINEAL
Melatonin
HYPOTHALAMUS
GnRH (Gonadotropin Releasing Hormone)
ANTERIOR PITUITARY
LH (Luteinizing Hormone) FSH (Follicle
Stimulating Hormone) PROLACTIN TSH (Thyroid
Stimulating Hormone) ACTH (Adrenal Cortical
Tropic Hormone) STH or GH (SOMATOTROPIN)
POSTERIOR PITUITARY
OXYTOCIN ADH (Antidiuretic Hormone)
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