Lecture 6 - Estrous Cycle

Question 1

Estrus

Answer 1

period of sexual receptivity in a female (aka Heat, Standing Heat)

Question 2

Estrous

Answer 2

describes a phenomena related to the reproductive cycle

Question 3

Anestrus

Answer 3

period when a female does not exhibit an estrous cycle

Question 4

Anestrous

Answer 4

describes a phenomena related to Anestrus

Question 5

Season

Answer 5

period of reproductive activity in seasonal breeding females

Question 6

Reproductive Cycle

Answer 6

provide the female with repeated opportunities to become pregnant
1. Estrous cycle
2. Menstrual cycle

Question 7

Polyestrus

Answer 7

uniform distribution of estrous cycles throughout the year (cattle, swine, rodents)

Question 8

Seasonal Polyestrus

Answer 8

estrous cycles occur only during a certain period (season) of the year
- short-day breeders (sheep, goat) = autumn breeding
- long-day breeders (mare) = spring breeding

*experience multiple estrous cycles within the season

Question 9

Seasonal monoestrus

Answer 9

one estrous cycle per year

Question 10

2 phases of estrous cycle

Answer 10

1. follicular
2. luteal

Question 11

Follicular phase

Answer 11

1. Proestrus = ovarian follicular development and E2 secretion
2. Estrus = mating behaviour, peak E2 secretion, LH surge and ovulation

Question 12

Luteal phase

Answer 12

1. Metestrus = CL formation and beginning of P4 secretion
2. Diestrus = sustained P4 secretion until CL regresses

Question 13

Anestrus

Answer 13

period when a female does not exhibit an estrous cycle

Question 14

Causes of anestrus

Answer 14

1. pregnancy = gestational anestrus
2. nursing = lactational anestrus
3. photoperiod = seasonal anestrus
4. nutritional status = nutritional anestrus
5. disease or infection = pathological anestrus

Question 15

Gestational anestrus

Answer 15

• lack of cyclicity is the 1st indication of pregnancy
• P4 from CL/placenta inhibits GnRH- FSH and LH release
• allows for embryonic/fetal development and uterine recovery post-partum

Question 16

Lactational Anestrus

Answer 16

• most mammalian females lack estrus while nursing
• metabolic necessity for energy conservation
• mammary, visual, olfactory, and auditory stimulation of lactation anestrus

Question 17

Factors that stimulate lactation anestrus

Answer 17

1. mammary stimulation - offspring suckling
2. visual stimulation - offspring in view
3. olfactory stimulation - offspring’s odour
4. auditory stimulation - offspring vocalization

Question 18

How many interactions/sucklings per day are needed to provide negative feedback on the hypothalamus to keep GnRH levels low?

Answer 18

threshold is 2

Question 19

Seasonal Anestrus

Answer 19

• evolutionary artifact to enhance embryonic and neonatal survival
  = early gestation during moderate temperatures
  = parturition when nutrients available to lactating mother
• controlled by photoperiod
  = hypothalamus exhibits GnRH “dormancy” during off-season

Question 20

Pineal gland

Answer 20

• located above the hypothalamus btw the hemispheres of the brain
• sensitive to environmental light and senses changes in photoperiod
• releases melatonin in response to dark
• melatonin alters many physiological processes including reproductive fxn
• pineal gland via melatonin regulates breeding activity in seasonal breeders

Question 21

How does the pineal gland regulate breeding activity in seasonal breeders?

Answer 21

• via melatonin which alters reproductive fxn

Question 22

Nutritional Anestrus

Answer 22

• evolutionary artifact to enhance maternal, embryonic and neonatal survival
  = poor nutritional status (decreased body fat) causes a lack of GnRH production by hypothalamus
• common in primiparous females (1st lactation)

Question 23

Pathological Anestrus

Answer 23

• causes can be numerous an multifactorial
  ex. uterine infection, persistent CL, cystic ovaries, mummified fetus