Untitled Quiz

Study Notes

Estrus refers to the period of sexual receptivity in female mammals.
Estrous refers to the cyclical development of follicles in female mammals, which differs from the menstrual cycle found in primates.
Anestrus occurs when a female is not experiencing repeated estrous cycles.

Polyestrus: More than one estrous cycle per year. Examples include cows, sows, and queens (induced ovulatory).
Seasonal Polyestrus: Cycles occur more than once in specific periods of the year.
- Short Day Breeders (SDB): Sheep, goats, and deer.
- Long Day Breeders (LDB): Horses and hamsters.

Cow:
- Cycle length: 21 days
- Estrus length: 18 hours
- Ovulation: 11 hours after estrus
- Pregnancy length: 282 days
Ewe:
- Cycle length: 17 days
- Estrus length: 29 hours
- Ovulation: Near the end of estrus
- Pregnancy length: 148 days
Sow:
- Cycle length: 21 days
- Estrus length: 48-72 hours
- Ovulation: 35-45 hours after the start of estrus
- Pregnancy length: 114 days
Mare:
- Cycle length: 21 days
- Estrus length: 4-8 days
- Ovulation: 3rd to 6th day of estrus
- Pregnancy length: 335 days
Bitch:
- Cycle length: 6 months
- Estrus length: 9 days
- Ovulation: 4-24 days after the start of estrus
- Pregnancy length: 63 days
Queen:
- Cycle length: 17 days (induced ovulator)
- Estrus length: 9 days
- Ovulation: Induced
- Pregnancy length: 63 days

Species	Type of Cycle	Follicular Development	Ovulation and CL Formation	CL Function
Cow, Ewe, Sow, Mare	Long	Spontaneous	Spontaneous	Spontaneous
Rats, Mice, Hamsters	Short (4 days average)	Spontaneous	Spontaneous (prolactin induced)	Induced
Rabbit, Cat, Mink, Ferret, Otter, Alpaca	Induced	Spontaneous	Induced (LH surge)	Spontaneous

The female estrous cycle is a repetitive sequence of physiological changes in the reproductive tract driven by hormonal interaction. It starts at sexual maturity and is interrupted by anestrus phases or pregnancy.
Key hormones and factors:
- Progesterone
- Prostaglandin F2α (PGF2α)
- Estradiol/Estrogen
- Follicle stimulating hormone (FSH)
- Luteinizing hormone (LH)

Proestrus:
- Progesterone levels decrease due to the regression of the old corpus luteum (CL) into the corpus albicans (CA) via the action of PGF2α (luteolysis).
- Maturation of one or two follicles occurs due to positive feedback from LH and estrogen.
Estrus:
- Ovulation typically occurs during estrus.
- A surge in LH levels triggers the mature follicle to rupture, releasing the ovum.
- The ruptured follicle develops into a new CL.
- Estrogen levels start to decline during this phase.
Metestrus:
- Start of the luteal phase, a period of sexual inactivity.
- The corpus luteum begins to develop.
- Progesterone levels increase as the CL matures, preparing the uterus for implantation.
Diestrus:
- Period of optimal CL activity with increased progesterone levels.
- If implantation of a fertilized ovum occurs, progesterone continues to be produced to support gestation.
- If no implantation occurs, the uterus secretes PGF2α to stop progesterone secretion and initiate another estrus cycle.

Induced ovulators like cats, rabbits, ferrets, and camels require a stimulus (typically physical copulation) to signal the anterior pituitary gland to release an LH surge, triggering ovulation.
In bitches, multiple matings create a greater and longer LH surge than single mating, increasing the chance of conception.

Factors contributing to Anestrus: Pregnancy, lactation, pathology, stress, nutrition, and season.
Gestational Anestrus: Progesterone during pregnancy has a negative feedback effect on GnRH, allowing time for uterine involution.
Seasonal Anestrus: Different photoperiods impact the activity of the pineal gland.
Lactational Anestrus: Suckling lowers LH levels, inhibiting ovulation. Prolactin inhibits GnRH release.
Nutritional, Pathological, and Stress-induced Anestrus: These factors can disrupt hormonal balance and affect reproductive cycles.