Repro test 3 (estrous cycle packet)

The estrous cycle is

a series of predicable reproductive events beginning with estrus and ending at the next estrus

Estrus

a noun describing the period of sexual receptivity in the female same as “heat”

estrous

an adjective used to describe the female reproductive cycle

oestrus 

the English derivative of estrus and estrous 

oestrus season

refers to several estrous cycles that occur during a certain season of the year (example: a mare)

polyestrous

animals that have an estrous cycle throughout the year ex: swine and cattle

seasonal polyestrous

animals that display clusters of estrous cycles that occur only during certain times of the year

short day breeders 

animals that cycle only when the days begin to shorten in the fall ex: sheep, goats and deer

Cyclicity

short photoperiods (fall/winter)

cyclicality process

light goes down → firing of retinal nerves decreases → decrease in excitation from SCG → decrease in inhibition of pineal gland → increase in melatonin→ increase in GNrH → increase in FSH and LH → cyclicality

long day breeders

animals the cycle only once the days begin lengthen in the spring EX mares 

monstrous

animals that have only once estrous cycle per year. EX dogs, wolves, foxes and bears

cats are

induced ovulators meaning she will ovulate only if copulation occurs. if she is not bred there is not ovulation and hence no CL to produce progesterone so she will return to heat in a few days

phases of the estrous cycle 

follicular phase and luteal phase

follicular phase

the period from regression of the CL until the time of ovulation, relativley short period of time (20% of the cycle), during the follicular phase the dominant ovarian structure is the dominant (graffian) follicle, during the follicular phase the principal reproductive hormone is estrogen

luteal phase 

the period of time form ovulation until regression of the CL, longer period of time (80% of the cycle), during luteal phase the dominant ovarian structure is the CL however follicle are developing during this phase, during the luteal phase the principal reproductive hormone is progesterone 

four stages of the estrous cycle

proestrus, estrus, metestrus, diestrus

proestrus

begins with progesterone declining as the result of luteolysis (destruction of the CL) and ends with the onset of estrus, the period of transition from progesterone dominance to estrogen dominance with FSH and LH being responsible for changing the dominance, the period when the follicles are recruited (selection 1 follicle to become dominant)

estrus 

the period of the estrus cycle that is recognizable by sexual receptivity and mating, estrogen is the dominant hormone, begins the early sign of estrus such as riding but not being ridden, vocalization and the increase in movement (restlessness), early in estrus the animal will not stand to be ridden but as estrus progresses the animal stand to be ridden by both males and females (standing estrus) 

metestrus 

the period between ovulation and formation of the CL, the period of both low estrogen and low progesterone, estrogen falls rapidly after ovulation and progesterone is not produced until the CL is 2-5 day “old”

Diestrus

the period associated with the functional CL where progesterone is at its highest, begins with the functioning CL and ends with luteolysis destroys the CL

Anestrus 

periods of time where the female does not exhibit a regular estrous cycle, due to a low level of GnRH. The ovary has neither follicular development nor a functioning CL (except during pregnancy). True anestrus is caused by a hormone insufficiency

apparent anestrus

failure to detect estrus or failure to recognize pregnancy

causes of Anestrus

pregnancy, lactation, nutrition, seasonal, stress, pathology and post partirme

pregnancy

The progesterone produced by the CL or the placenta inhibit the production of GnRH

lactation

all most all mammals except the horse and alpaca have a period of anestrus associated with lactation. This is related to the suckling of the offspring and lasts for variable amounts of time, apparently the actual teat stimulation is not the cause but rather the presents of the calf, visual, olfactory or auditory stimuli.

The sow has a true lactational anestrus, she will ovulate 4-8 days after weaning.

dogs do not show lactational anestrus and some cats do some don’t and may even breed while lactating

nutritional

lack of adequate nutrition in the form of protein and or energy is one of the more common causes of anestrus. Characterized by low levels of GnRH, FSH and LH and small inactive ovaries. In beef cattle most commonly seen in primiparous animals the demand of lactation and growth exceeds the amount of energy provided by the ration. not as common in multiparous females because there is little demand for growth.

dairy cattle nutritional

nutritional anestestous is a very common and serious problem. The high level of milk production often means that the cow can not consume enough nutrients (usually energy) to overcome the demands of lactation. These cattle are said to be in a negative energy balance, with consumption lagging behind the production of milk.

Doc’s opinion- mother natures order of things

1- take care of mama

2- take care of baby

3- growth of mama if possible

4-breeding back comes last

These cows do not cycle until

Energy requirements of lactation are meet, until that time the cow is utilizing fat reserves to meet the energy requirements

Seasonal

An evolutionary adaptation to ensure the offspring are born at the season of the year which allows for the greatest chance of survival. Characterized by hypothalamic dormancy as seen above the photoperiod is the determining factor, sunlight affects the pineal gland which determines the release of melatonin. Melatonin allows for the release of GnRH from the hypothalamus.

Stress

While often related to nutrition can be a source of anestrus, particularly extreme heat

Pathology

Conditions such as cystic ovaries (luteal cysts), pyometria, mucometria and others

Postpartum

A normal anestrus which allows for uterine involution this alone is usually a short period

Menstrual cycle

The events that occur between two menstrual period, average duration of cycle is 28 days (24-35 days), Menes (menstruation) of the endometrium of the uterus, commonly referred to as the menstrual period

The two major differences between the menstrual cycle and estrous cycle are

1- Menes (the sloughing if the endometrium) does not occur in animals

2-in the estrous cycle the recognizable sign in estrus (standing heat) in the menstrual cycle the recognizable sign is Menes. Thus in the estrous cycle ovulation occurs at day 1, however in the menstrual cycle ovulation occurs at day 14

The menstrual cycle is divided in 2 phases

Follicular phase and luteal phase

Follicular phase

Composed of 2-5 days of Menes followed by 9 days of proliferation of the endometrium in response to rising levels of estrogen. The follicular phase last 14 day or about ½ of the cycle begins with Menes and ends with ovulation. Following Menes there is a gradual increase in GnRH the increase in estrogen. At a point about 14 days following Menes LH, FSH, and estrogen rise dramatically causing ovulation. The follicular phase occurs at the came time as the proliferation phase.

Luteal Phase

Begins with ovulation and last until Menes. Following ovulation the CL produces progesterone and only in humans the CL also produces estrogen which causes the thickening of the endometrium to provide an optimal environment for implantation of the embryo. If pregnancy does not result the CL is destroyed by luteolysis and Menes begins. The luteal phase occurs at the same time as the secretory phase.

The proliferative and secretory phase

Refers the endometrium of the uterus

Menopause

A form of anestrous that exists in humans but is not recognized in animals. At puberty the average woman has about 300,000 oocytes with follicles in the ovaries. By the age of menopause (45-50) she has 0 oocytes left. Tons will become arctic (develop then die before ovulation) the little bit left will read maturity and be ovulated

In woman menopause is caused by

A depletion of follicle within the ovary. Without follicle there is no production of estrogen, also without follicle there is no CL to produce progesterone which is responsible for driving the menstrual cycle.

Signs of menopause are related to the deficiency of estrogen

Genital atrophy

Decreased secretions of repro tract

Modification of Lipid metabolism

Increase in bone loss (osteoporosis)

Vasomotor symptoms (hot flashes)

Amenorrhea-the absence of Menes in woman is caused by

Nutritional along with high levels of activity

Post partum

Lactational