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Questions and Answers
What is the initial state of primordial follicles in the ovary?
What triggers the ovulation process in spontaneous ovulators?
Which phase follows oocyte maturation?
In which species does ovulation occur solely through the ovulation fossa?
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What is the time of ovulation in cows relative to the duration of estrus?
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How many waves of 7 days each are observed in follicular dynamics for cows?
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In which species does ovulation occur in response to mechanical stimulation of the cervix?
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What is luteolysis initiated by in the female reproductive system?
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What happens to the dominant follicle in the presence of progesterone?
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Which hormone facilitates the structural regression of the corpus luteum during luteolysis?
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What does the term 'folliculogenesis' refer to?
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What happens during the functional luteolysis phase?
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Which species has the shortest duration of estrus?
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Which hormone is crucial for stimulating nuclear maturation of oocytes?
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What is the role of PGF2α in the luteal tissue during luteolysis?
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How is uterine PGF2α transferred to the ovary in cows?
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What behavior indicates a mare is in estrus?
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Which of the following is NOT a sign of heat in a she-camel?
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What is a characteristic behavior of a doe or she-goat in heat?
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What is indicated by the presence of cervical mucus in ewes during heat?
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What phenomenon occurs during the she-camel's heat cycle?
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What characterizes the estrus phase in terms of hormonal changes?
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During which phase does the cow exhibit standing estrus, indicating readiness to be mounted?
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What is the typical duration of the diestrus phase?
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What structural change is associated with the metestrus phase?
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What physiological phenomenon may occur in cows 48 hours after estrus?
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Which sign of heat indicates that a cow is in early estrus?
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What is the nature of the mucus during heat, particularly characterized by arborization?
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The duration of estrus in cows is approximately how long?
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What is the process known as that involves the removal of seminal plasma protein during sperm maturation?
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During fertilization, which event occurs after the acrosomal reaction?
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What does the conceptus do to maintain P4 production after fertilization?
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What phase of the estrous cycle is characterized by the preparation of the female tract for mating?
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Which is the correct critical time for maternal recognition of pregnancy in bovine and ovine species?
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Which phase of the estrous cycle accounts for 80% of the cycle duration?
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What happens during the cortical reaction after sperm-oocyte fusion?
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What is the correct order of events for fertilization starting from the initial sperm activity?
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Study Notes
Female Reproductive Physiology
- Folliculogensis is the development of follicles within the ovary.
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Follicular growth: thousands of primordial follicles are dormant in the ovary. Some are recruited through unknown mechanisms, responding to increased Follicle Stimulating Hormone (FSH). A few follicles are selected, with one or more continuing to grow until dominance.
- The dominant follicle can either ovulate in response to a surge in Luteinizing Hormone (LH) (in the absence of progesterone (P4))
- Or undergo atresia (degeneration) in the presence of P4 dominance and low LH.
Follicular Dynamics
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Follicular dynamics: refer to the wave pattern of follicular growth and regression of a group of ovarian follicles.
- This ends with ovulation of preovulatory dominant follicle(s).
- These dynamics continue throughout the cycle, not only during estrus.
- Cows experience mainly 3 waves of 7 days each.
- Mares have 2 waves of 10-12 days.
Oocyte Maturation
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Oocyte maturation:
- Consists of periods of growth and nuclear and cytoplasmic maturation.
- The oocyte starts to grow after primordial follicle selection.
- After oogenesis, the nucleus remains in a resting state until the preovulatory LH surge (oocyte maturation inhibitor; OMI effect).
- Preovulatory LH stimulates nuclear maturation (meiosis) and cytoplasmic maturation.
Ovulation
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Ovulation: the rupture of the mature Graafian follicle(s) in response to the preovulatory LH surge stimulated by threshold levels of estrogen.
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Spontaneous (hormonal) ovulation:
- Occurs in cows, buffalo-cows, ewes, does and mares.
- Triggered by hormonal changes including estrogen peak and preovulatory surge LH.
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Induced (reflex or neural) ovulation:
- Occurs in queens, she-camels, and rabbit does.
- Occurs in response to stimulation of the cervix/vagina.
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Spontaneous (hormonal) ovulation:
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Site of ovulation:
- In mammals (cows, buffalo-cows, ewes, does, and she-camels): ovulation occurs in any site on the ovarian surface except the hilus
- In mares: ovulation only occurs through the ovulation fossa.
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Factors involved in ovulation:
- Prostaglandin E2 (PGE2): increases blood flow to the ovary and dominant follicle, promoting PGF2α secretion, which leads to increased blood flow to the follicle;
- Luteinizing Hormone (LH) surge: shifts dominant follicle secretion from estrogen (E2) to progesterone (P4).
- Prostaglandin F2α (PGF2α): increases contraction of smooth muscles in the follicle, causing release of lysosomal enzymes and collagenase. This leads to follicle wall weakening and follicular pressure.
Time of Ovulation
- Species | Estrous cycle Length (Days) | Estrous cycle Duration (Hours) | Time of ovulation
- Cow | 21-23 | 10-19 | 10-12 hours after the end of estrus
- Buffalo-cow | 18-22 | 17-24 | 30-36 hours from the onset of estrus, or 10-12 hours after the end of estrus.
- Ewe | 16-17 | 24-36 | 18-24 hours after the onset of estrus
- Goat | 21 | 20-25 | 18-24 hours after the onset of estrus
- Mare | 19-25 | 4-8 days | 1-2 days before the end of estrus
- She-camel | 24 | 5 days | 30-40 hours after coitus, or 35-45 hours after the onset of estrus
- Sow | 21 | 48-72 | 35-45 hours after the onset of estrus, or 1-2 days before the end of estrus
Luteolysis
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Luteolysis is the destruction or decomposition of the corpus luteum (CL) leading to a decrease in circulating P4.
- It begins with functional luteolysis: a decrease in P4, followed by structural regression: connective tissue scar deposition, forming the corpus albicans.
- Initiated by uterine PGF2α, followed by ovarian oxytocin and ovarian PGF2α which vasoconstricts luteal tissue.
- Uterine PGF2α is transferred through the utero-ovarian vein and artery, primarily from the ipsilateral uterine horn in cows (countercurrent passive diffusion).
Conception and Fertilization
- Conception starts with various maturational changes in the sperm-egg complex.
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Fertilization: requires synchrony between ovulation and insemination due to the short lifespan of ova and sperm.
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Sperm capacitation is essential for fertilization. It includes:
- Decreased intracellular pH
- Influx of extracellular Ca++ ions
- Removal of seminal plasma protein
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Sperm capacitation is essential for fertilization. It includes:
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Steps of Fertilization:
- Hyperactive sperm motility: allows the sperm to reach the egg with increased rapid movement.
- Binding to Zona pellucida (ZP): a species-specific interaction through receptor-ligand binding.
- Acrosomal reaction: the fusion of the inner and outer membranes of the sperm acrosome, releasing enzymes that create tunnels in the ZP.
- Sperm-oocyte membrane fusion: fusion of the oocyte plasma membrane with the sperm head membrane.
- Cortical reaction: prevents any additional sperm from entering the egg.
- Formation of pronuclei: following fusion of the male and female pronuclei (syngamy), the zygote begins development.
Maternal Recognition of Pregnancy
- Following successful fertilization, the conceptus maintains P4 production by signaling its presence to the maternal system.
- Bovine and Ovine: the conceptus secretes steroid hormones and proteins, including interferon tau between day 12 and day 21 of pregnancy. This protein inhibits the production of uterine PGF2α. The critical time for recognition is from day 15 to day 16.
- Mare: the conceptus migrates within both uterine horns 10-12 times per day between day 10 and day 16 of pregnancy. The critical time for recognition is from day 12 to day 14.
Estrous Cycle
- Estrous cycle: the period between two successive heats (periods of sexual receptivity). It is defined as the repeated opportunity for the female to be pregnant.
Phases of Estrous Cycle
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Follicular phase (20% of the cycle):
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Proestrus: prepares the female tract for sexual receptivity and mating.
- Starts with the destruction of the CL and ends with the start of estrus.
- Duration: 2-4 days.
- Hormonal: shifts from P4 dominance to E2 dominance.
- Structure: Growing follicles, absence of CL.
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Estrus/Heat: period of sexual receptivity.
- Duration: About one day.
- Hormonal: characterized by high threshold levels of E2 which stimulates more FSH and LH, increasing inhibin. This leads to selective inhibition of FSH, and ultimately results in a surge in LH and ovulation
- Structure: Dominant mature Graafian follicles (MGF) with absence of CL.
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Proestrus: prepares the female tract for sexual receptivity and mating.
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Luteal phase (80% of the cycle):
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Metestrus: begins with ovulation and ends with the formation of a full functional CL.
- Duration: 2-5 days.
- Hormonal: shifts from E2 dominance to P4 dominance.
- Structure: Corpus hemorrhagicum (softer than CL/mushy) due to luteinization (conversion of follicular cells into luteal cells) of the follicular cells after ovulation.
- Metrorrhagia: (metestral bleeding 48 h after estrus) - a physiological phenomenon in cows (80% of heifers).
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Diestrus: the period of maximum luteal function.
- Starts with the formation of a full functional CL and ends with luteolysis.
- Duration: 10-14 days.
- Hormonal: P4 dominance.
- Structure: Full functional mature CL with the presence of follicles of different sizes (small, medium, large).
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Metestrus: begins with ovulation and ends with the formation of a full functional CL.
Signs of Heat (Estrus)
- Early Estrus: the cow mounts other animals, but refuses to be mounted.
- Standing Estrus: the cow accepts to be mounted by other animals and exhibits lordosis.
- Increased vocalization (bellowing)
- Decreased appetite
- Rosy red vaginal mucous membrane
- Decreased milk yield
- Increased movement and restlessness
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Estral mucous: a transparent, viscous mucous discharge from the vulva.
- May soil/contaminate the tail and hindquarters
- Characterized by "arborization" in a dry film. (fern-like pattern)
Arborization
- Arborization is observed when a thin layer of estrous mucus on a glass slide is allowed to dry. The fern-like pattern is due to the crystallization of electrolytes, especially sodium chloride, on the mucus fibers. This is caused by high E2 levels from the preovulatory follicle.
Signs of Heat in a Mare
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Introduction of teaser animal:
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Mare in estrus:
- Stands back to face the stallion (calm and not kicking).
- Winking: rhythmic opening of vulval lips with exposure and rhythmic contraction of the clitoris (associated with drippling).
- Drippling: frequent urination and tail raising.
- Squatting: abduction and opening of hind limbs.
- Swinging the rear quarter toward the teaser.
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Mare NOT in estrus:
- Stands face to face with the teaser.
- May exhibit aggressive behavior and kick the teaser.
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Mare in estrus:
Signs of Heat in a She-camel
- Restlessness: seeks the camel-bull and stays close to him, tail wagging.
- Frequent squatting and straddling of the hind limbs.
- Secretes characteristic pheromones from the pole gland behind the ear.
- Rutting phenomenon "Dulla/Gulla/Kolla/Pulla" (protrusion of soft palate) in the camel-bull.
- Slight vulval swelling with a small amount of mucus.
- The cycle consists of recruitment (4d), growth (6-10d), mature (7-9d), and regression (7-12d).
Signs of Heat in a Ewe
- Male seeking behavior
- Restlessness
- Cervical mucous hidden under the fatty tail
Signs of Heat in a Doe/She-goat:
- Male seeking behavior
- Restlessness
- Tail wagging
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Description
Test your knowledge on female reproductive physiology, focusing on folliculogenesis and the dynamics of ovarian follicles. This quiz covers key concepts such as follicular growth, ovulation, and the hormonal roles during the reproductive cycle. Perfect for students studying animal reproduction.
