Reproductive Cyclicity
Estrus
Menstrual Cycle 
Begins at Estrus (heat) and ending at the subsequent estrus
Provide females with repeated opportunities to copulate and become pregnant
When pregnancy occurs the female enters a period of anestrus that ends after parturition, uterine involution (acquisition of normal uterine size and function), and lactation
Terminology for reproductive cyclicity
Estrus: a noun " the cow is displaying estrus" also called heat
Estrous: an adjective "the length of the estrous cycle in the pig is 21 days"
Season is another common term used to describe a reproductive pattern
-us is behavior, ex: the female is experiencing anestrus
-ous refers to the cycle
3 types of cyclicity
Seasonally polyestrus- go into estrus in different seasons, ex. sheep and goats are short-day breeders (begin to cycle when day length decreases like in fall), horses are long day breeders (when the day length increases in spring she cycles)
monoestrus- one cycle per year, dogs, wolves, foxes, bears
Polyestrus- uniform distribution of estrus cycles
Estrous cycle
2 phases of estrous cycle
Follicular phase
Luteal phase
regression of corpa lutea to ovulation
relatively short 20% of cycle
secrete primary reproductive hormone estradiol (from follicle)
large antral follicle = the primary ovarian structure
ovulation until corpus luteum regresses
80% of cycle
corpora lutea= the primary ovarian structure
progesterone (secreted by corpora lutea) = the primary hormone
4 stages of Estrous cycle
estrus = sexual receptivity + peak estrogen secretion
metestrus = CL formation + beginning of progesterone secretion
Proestrus = formation of ovarian follicles + estrogen secretion
diestrus = sustained luteal secretion of progesterone
Follicular phase= Proestrus + Estrus
luteal phase= Metestrus + diestrus
During early period will not accept male for mating as estrus progresses she become more willing/ standing estrus during this time she displays mating posture/ lordosis
ovulated follicle changes to CL in a process called leutinization
longest stage
Cycle of the bitch and queen is different
Bitch cycle has: anestrus, proestrus, estrus and diestrus, long anestrus so she displays 2 estrus cycles in three years
superfecundation can happen where multiple ovulations produce multiple oocytes than can be fertilized by spermotozoa of different males
queen cycle: proestrus, estrus, postestrus, diestrus and anestrus. They are induced to ovulate through copulation in a constant follicular phase until copulation happens then corpus luteum forms
Anestrus "without Estrus (heat)"
ovaries are inactive no CL is present
result of insufficient GnRH release
true anestrus- insufficient hormonal stimuli
apparent anestrus - failure to detect estrus or failure to recognize the female is pregnant
Anestrus can be caused by: pregnancy, lactation, presence of offspring, season, stress, pathology
Pregnancy/ gestational anestrus is a normal condition caused by inhibition of GnRH by progesterone
Seasonal anestrus- transition from seasonal anestrus to estrus is controlled b y photoperiod, during this time animals can ovulate a folicle with no estrus behavior known as silent ovulation
onset of seasonal cyclicity is similar to onset of puberty
lactational anestrus prevents a new pregnancy before young are weaned
mammary stimulation is not totally responsible for lactational anestrus
anestrus can result from negative energy balance
the menstrual cycle differs from the estrous cycle
no defined period of sexual receptivity
a period of endometrial sloughing called menses (menstruation)
the timeline for description of the cycle begins with menses not ovulation or estrus
the follicular phase = menses (5 days) + proliferative phase (9 days)
Luteal phase = secretory phase (12 days)
Amenorrhea is the human equivalent to anestrus. It can be caused by: menopause, low nutritional intake, lactation