What is estrous cycle?
The physiologic changes that are induced by reproductive hormones in most mammalian placental females.
Meaning of estrous?
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
Estrous cycles are interrupted by what phase?
Anestous phases or pregnancies
Polyestrous meaning?
Have more than one period of estrus in a year.
Eg - cattle and pigs
Definition and examples of short-day breeders
Animals that are sexually active in fall or winter.
eg: sheep, goats and deer
Definition and examples of long-day breeders
Animals that are sexually active in spring and summer
eg- horses, harmsters and ferrets
Monoestrus
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)
Estrous cycle
- 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
Proestrus
- 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
Estrous
- 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
Estrogen from graafian follicle stimulate
increases in LH
If there is no copulation in an induced ovulator, what happens?
Estrus may continue for many days, followed by ‘inter-etrus’, and the etrus phase starts again until copulation and ovulation occur
Metestrus
- 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
Diestrus
- 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.
Time of ovulation
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
Anestrous
- Not cycling
- Causes: pregnancy, presence of offspring, seasonal, stress, pathological condition (COD or Folicular Cysts, Pyometra - uterine infection)
Anestrous -Gestational
(normal)
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
What is summer heat stress
when the temperature humidity index combined effects of heat and humidity produce a high apparent temperature
#associated with progesterone level
Anestrous - lactational
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
Anestrous - Nutritional
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
Estrus synchronization
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
