Reproductive Cyclicity

Estrus

Menstrual Cycle Screen Shot 2022-11-15 at 9.43.09 PM

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 Screen Shot 2022-11-15 at 5.52.16 PM

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 Screen Shot 2022-11-15 at 6.07.12 PM

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 Screen Shot 2022-11-15 at 6.11.04 PM

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 Screen Shot 2022-11-15 at 6.19.08 PM

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 Screen Shot 2022-11-15 at 6.25.43 PM

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 Screen Shot 2022-11-15 at 6.32.05 PM

onset of seasonal cyclicity is similar to onset of puberty Screen Shot 2022-11-15 at 6.36.06 PM

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