Estrous cycle

Question 1

What is estrous cycle?

Answer 1

The physiologic changes that are induced by reproductive hormones in most mammalian placental females.

Question 2

Meaning of estrous?

Answer 2

Period of reproductive cyclicity and period of sexual receptivity
- Females are only sexually active during the estrus phase of their cycle
- Referred as being in heat

Question 3

Estrous cycles are interrupted by what phase?

Answer 3

Anestous phases or pregnancies

Question 4

Polyestrous meaning?

Answer 4

Have more than one period of estrus in a year.
Eg - cattle and pigs

Question 5

Definition and examples of short-day breeders

Answer 5

Animals that are sexually active in fall or winter.
eg: sheep, goats and deer

Question 6

Definition and examples of long-day breeders

Answer 6

Animals that are sexually active in spring and summer
eg- horses, harmsters and ferrets

Question 7

Monoestrus

Answer 7

Experience estrus once each year or breeding season
Typically in spring to allow growth of offspring during the warm season to survive the next winter
EG- bears, wolves(mostly carnivores)

Question 8

Estrous cycle

Answer 8

• Period of acceptance of male
• Increased mucus secretion, stringy and clear
• Ovulation occurs where there are ferning pattern of mucus and relaxed cervix
• In cat, rabbit and camel, ovulation is induced by coitus,
• Other animals’ ovulation are spontaneous. Called as follicular phase.
• Estrous controls physiological changes of proestrus and estrus

Question 9

Proestrus

Answer 9

• One/several follicles from ovary starts to grow
• Estrogen increases and level peaks
• Under estrogen influence, the lining in the uterus starts to develop
• Not yet sexually receptive

Question 10

Estrous

Answer 10

• Phase when female is sexually receptive
• Under regulation by gonad hormones, ovarian follicles are maturing and estrogen secretions exert their biggest influence
• Exhibits a sexually receptive behaviour, a situation that may be signaled by visible physiological changes
• Lordosis reflex, in which the animal spontaneously elevates her hindquarters
• Cervical mucus volume increases
• Sperm transport is optimal
• In some species, the vulvae are reddened

Question 11

Estrogen from graafian follicle stimulate

Answer 11

increases in LH

Question 12

If there is no copulation in an induced ovulator, what happens?

Answer 12

Estrus may continue for many days, followed by ‘inter-etrus’, and the etrus phase starts again until copulation and ovulation occur

Question 13

Metestrus

Answer 13

• estrogen stimulation subside and corpus luteum starts to develop
• Uterine lining begins to secrete small amounts of progesterone
• Endometrial glands continue to grow and become coiled, preparing the uterus for the embryo

Question 14

Diestrus

Answer 14

• Characterized by the activity of the corpus luteum that produces high amount of progesterone
• Absence of pregnancy ; the diestrus phase terminates with the regression of the corpus luteum
• Uterus releases PGF2a
• If CL regresses, progesterone in blood decreases and grafian follicle begin final development that occurs in proestrous for ovulation at estrus.
• Estrous cycle starts over.

Question 15

Time of ovulation

Answer 15

Ewe: 30-36 hours from beginning of estrus
Doe: 12-24 hours after onset of estrus
Sow: 35-45 hours from beginning of estrus
Cow: 10-11 hours after end of estrus
Mare: 1-2 days before end of estrus

Question 16

Anestrous

Answer 16

• Not cycling
• Causes: pregnancy, presence of offspring, seasonal, stress, pathological condition (COD or Folicular Cysts, Pyometra - uterine infection)

Question 17

Anestrous -Gestational
(normal)

Answer 17

CL present during pregnancy
- Progesterone has -ve feedback on GnRh
- LH and FSH don’t surge
- Estrogen remains low to moderate

CL regresses before parturition but hypothalamus still does not increase GnRH pulse frequency and amplitude for a while
- due to long inhibition of hypothalamus during gestation
- allow for uterine involution prior to the first post partum estrous cycle

Question 18

What is summer heat stress

Answer 18

when the temperature humidity index combined effects of heat and humidity produce a high apparent temperature
#associated with progesterone level

Question 19

Anestrous - lactational

Answer 19

Suckling can trigger the anestrous
- sow can completely supresses estrus
- cow can be suppressed for up to 60 days
- suckling frequency (2x/day)
- Prolactin’s role to inhibit GnRH release

Question 20

Anestrous - Nutritional

Answer 20

Negative energy balance
- Similar to puberty in that inhibit GnRH pulse frequency because insuffient energy available

Problem in primiparous females with combined requirements of lactation and growth

Question 21

Estrus synchronization

Answer 21

Group female for parturition
- decrease labour, standardize calving period
- more uniform weaning weights
Reduce time required for estrus detection
Eliminate estrus detection with timed insemination
Use of progesterone for estrus synchronization

Principle
- maintain the cow under the influence of progesterone until corpus luteum regresses, remove progesterone, animal respond to progesterone removal with estrus 2-5 days later
Estradiol valerate and norgestomet (estrogen/progesterone formulation)
- implant norgestomet (progestagen)
Injection allows for rapid increase in progestin in blood, while the implant initiates its release over several hours