BOVINE OVULATIONPRESENTED BY: ASAD ULLAH BABER 08-ARID-256

OVULATIONy Ovulation is the process in a female's estrous cycle

by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg). y The time immediately surrounding ovulation is referred to as the ovulatory phase or the periovulatory period.

Estrous Cycle Length of the estrous cycle Average 21 days (range 18 to 24 days) Estrus (standing heat) 12 to 18 hours (range 8 to 30 hours) Ovulation Approximately 30 hours after the beginning of standing heat (or 12 to 18 hours after the end of standing heat)

Estrous Cycle

Major structures on the ovary are

Follicle a blister-like structure containing the egg (referred to as oocyte); produces hormone estrogen

High amount of estrogen causes standing heat and ovulation

Corpus luteum (referred to as CL) looks like a hard yellow structure and produces hormone progesterone that is responsible for maintenance of pregnancy

Follicle DevelopmentFollicular WaveDomina nce Grow th Selectio n Recruitme nt Next Recruitmen t Regressi on

Follicle development occurs as a wave-like pattern consisting of Recruitment, Selection, Growth, Dominance, and Regression phases Usually 2 to 4 follicular waves occur during the estrous cycle in cattle

Follicle DevelopmentFollicle Stimulating Hormone (FSH)Regressi on Next Recruitmen tFSH FSH

Recruitme nt

FSH precedes recruitment of follicles (causes follicles to start growing) FSH is the same hormone used for superovulation and embryo transfer in cattle

Follicle DevelopmentLuteinizing Hormone (LH)Dominan ce Growt h Selection Regressio n

LH pulses

LH promotes further follicle growth and maturation of egg

Endocrinology During the Estrous CycleFollicle Stimulating Hormone (FSH)Ovulatio n Ovulatio n

Estrus

FSH

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Day of the Estrous Cycle

Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Estrus

Endocrinology During the Estrous CycleLuteinizing Hormone (LH)Ovulatio n LH Surge LH Surge Ovulatio n

Estrus

LH pulses 0 2 4 6

LH pulses 18 20 0

8 10 12 14 16 Day of the Estrous Cycle

Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Estrus

Endocrinology During the Estrous CycleEstrogenOvulatio n Ovulatio n

Estrus

Estrogen

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Day of the Estrous Cycle

Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Estrus

Physiology and Endocrinology of the Estrous Cycle

Estrus

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8 10 12 14 16 Day of the Estrous Cycle

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Relationships among structural and hormonal changes during the 21-day estrous cycle (example shown for cattle having 3 follicular waves)

Estrus

y The beginning of each wave is characterized by a

y y y y

small rise in FSH followed by rapid growth of numerous follicles. From this wave of follicles, one follicle is selected to grow to a much larger size than the others. This dominant follicle has the ability to regulate or restrict growth of all other follicles on the ovary. Dominant follicles only remain dominant for a short period of time, 3 to 6 days. This is followed by either cell death and regression or ovulation and release of the egg.

Ovulation Processesy Symptoms associated with acute inflammation y Thecal layer becomes edematous y Acute hyperemia y Granulosa cells of follicles dissociate y Oocyte freed from the cumulus pedicle and

underlying mural granulosa y The thecal C.T network is degraded

Conty On apical surface of the follicle a stigma forms y Extrusion of fluid y A decline in the tensile strength of the follicular wall y Bleeding at ovulation from disrupted vesselss

Detail of processy Manifestations of the ovulatory process are similar to

those symptoms associated with acute inflammation. y During the preovulatory period the thecal layer becomes edematous and the antrum accrues additional fluid y As a result of acute hyperemia (vasodilation, increased capillary/venule permeability). Granulosa cells of preovulatory follicles dissociate and the oocyte (with adhering corona radiata) is freed from the cumulus pedicle and underlying mural granulosa. y The thecal connective tissue network is degraded during the immediate preovulatory period; breakdown is associated with vascular damage, adhesion of platelets to endothelium.

y Along the apical surface of the follicle an avascular stigma y y y y y y

forms marking the time of impending rupture. Extrusion of fluid through the stigma occurs in a passive manner. There is no substantial increase in intrafollicular pressure as rupture approaches A decline in the tensile strength of the follicular wall allows disruption to occur at a constant (ie., capillary) pressure. There is some bleeding at ovulation from disrupted vessels adjacent to the stigma. The timing of follicular rupture following the onset of the surge of LH. Larger-framed species farm animals ovulate approximately 24 to 36 hours following the preovulatory rise in LH.