Animal Reproduction and Estrous Cycle Review

Practice flashcards covering reproductive anatomy, estrous cycles, pregnancy, parturition, modern reproductive technologies, and hormonal control across livestock species.

What is the key difference between estrus and estrous?

Estrus is the specific period in which a female animal will stand to be bred, whereas estrous refers to the entire period from one heat cycle to the next.

How are livestock species categorized according to their estrous cycle patterns?

They are categorized as polyestrus (displaying cycles uniformly throughout the entire year), seasonally polyestrus (displaying multiple cycles during a specific season), or monoestrus (displaying only one period of sexual receptivity per year).

What are the two main phases of the estrous cycle and their approximate proportions of the total cycle?

The follicular phase accounts for approximately $20\%$ of the cycle (dominant follicle growth and increased estradiol), while the luteal phase accounts for approximately $80\%$ of the cycle (corpus luteum formation and increased progesterone).

What four stages comprise the full estrous cycle?

Proestrus and estrus (comprising the follicular phase), and metestrus and diestrus (comprising the luteal phase).

What characterizes the diestrus stage of the estrous cycle?

Diestrus is the longest stage of the estrous cycle, characterized by the sustained release of progesterone by the corpus luteum.

What is anestrous, and what factors can cause it?

Anestrous is a condition in which the female does not cycle due to insufficient hormonal stimuli; causes include pregnancy, lactation, presence of offspring, season, stress, and pathology.

What are the average estrous cycle length, estrus duration, and timing of ovulation for a cow?

The average estrous cycle length is $21\,\text{days}$, estrus duration is $18\,\text{hours}$, and ovulation occurs $12\,\text{hours}$ after the end of estrus.

What are the average estrous cycle length, estrus duration, and timing of ovulation for a mare?

The average estrous cycle length is $22\,\text{days}$, estrus duration is $7\,\text{days}$, and ovulation occurs $24\,\text{hours}$ before the end of estrus.

What are the recommended male-to-female breeding ratios for beef cattle, dairy cattle, and hogs in natural service?

Beef cattle ratio is 1: 25-35, dairy cattle ratio is 1: 20-25, and hogs ratio is 1: 15-18.

What components are evaluated during a Breeding Soundness Evaluation (BSE)?

Physical condition, normal structure of reproductive organs, and semen quality (including volume, sperm concentration, motility, and percentage of normal sperm cells).

What sperm cell structural abnormalities are illustrated in this diagram?

The diagram illustrates a proximal droplet, a bent tail, and a detached tail.

What are the primary functions of the ovaries?

Production of oocytes (ova or eggs) inside developing follicles and production of the hormones estrogen and progesterone.

What are the three main anatomical divisions of the oviduct?

The infundibulum, ampulla, and isthmus.

What defines a duplex uterus, and which species exhibit this anatomy?

A duplex uterus features two distinct cervices; it is present in marsupials (such as opossums, which have 2 vaginas) and rabbits and mice (which have 1 vagina).

How do bicornuate and simplex uterine structures differ?

A bicornuate uterus has two uterine horns and one cervix (found in cows, mares, ewes, sows, bitches, and queens), whereas a simplex uterus has a single large uterine body with no uterine horns, one cervix, and one vagina (found in primates and women).

What are the primary functions of the cervix?

Serving as a passageway and storage reservoir for sperm cells, acting as a barrier between external and internal environments, providing lubrication, and acting as a passageway for the fetus at parturition.

What are the three parts of the broad ligament and their respective suspension functions?

The mesometrium supports the uterus, the mesosalpinx surrounds and supports the oviduct, and the mesovarium attaches the ovary to the mesometrium.

What anatomical and reproductive differences distinguish female poultry from mammals?

Poultry lay eggs outside the body, do not suckle young, lack well-defined estrous cycles or pregnancy, and only the left ovary and oviduct develop.

What are the five parts of the poultry oviduct and their roles in egg formation?

Infundibulum (picks up yolk, fertilization site; $15\,\text{min}$), Magnum ($40\text{--}50\%$ thick albumen laid down; $3\,\text{hours}$), Isthmus ($10\%$ albumen and shell membranes; $1.25\,\text{hours}$), Uterus/shell gland ($40\%$ albumen, shell, and pigment formed; $20.75\,\text{hours}$), and Vagina/Cloaca (passage as egg is laid).

What are the three parts of the epididymis and its primary functions?

The head (caput epididymidis), body (corpus epididymidis), and tail (cauda epididymidis); its functions are concentration, storage, maturation, and transport of spermatozoa.

How do fibroelastic and vascular penis types differ in structure, mechanism, and species occurrence?

Fibroelastic penises (bull, ram, boar) contain an S-shaped sigmoid flexure, retractor penis muscle, and limited erectile tissue; vascular penises (stallion, dog, cat, human) lack a sigmoid flexure and enlarge through blood engorgement of erectile tissue.

What is the function of the amnion as an extraembryonic membrane?

The amnion surrounds and encloses the fetus in a fluid-filled cavity, protecting the embryo against mechanical damage and preventing tissue adhesions.

How are placental types classified by chorionic villi distribution, and which species belong to each type?

Diffuse (sow and mare), Cotyledonary (ruminants), Zonary (dog and cat), and Discoid (primates and rodents).

What are the maternal and fetal components of a ruminant placentome?

The caruncle is the maternal side, and the cotyledon is the fetal side.

At what stage of gestation does the placenta take over dominant progesterone production in ewes versus mares?

In ewes, the placenta assumes the dominant role at $50\,\text{days}$; in mares, it assumes the dominant role at $70\,\text{days}$.

What are the average gestation lengths in days for cows, mares, and sows?

Cow: $283\,\text{days}$, Mare: 336-340$\,\text{days}$, and Sow: $114\,\text{days}$.

What hormonal cascade initiates parturition?

Fetal stress or uterine crowding triggers cortisol release from the fetal adrenal cortex, leading to decreased progesterone and increased estrogen, Prostaglandin $F_{2\alpha}$, and oxytocin.

What is dystocia?

Dystocia is abnormal or difficult parturition requiring assistance to prevent death of the newborn and dam.

What milestone occurred in $1780$ regarding reproductive technology development?

The first successful artificial insemination was achieved in a dog model.

What percentage of matings are conducted via Artificial Insemination (AI) in dairy cattle, swine, and turkeys?

Dairy cattle: 80-90$\%$, Swine: 80-85$\%$, and Turkeys: $100\%$.

What three methods are used for semen collection in males?

Artificial vagina, electroejaculator (rectal probe supplying mild electrical waves), and manual stimulation.

What four parameters are evaluated during semen processing?

Motility (movement), Morphology (structure/shape), Concentration (density per milliliter), and Viability (percentage of live cells).

What four procedure types are used for female artificial insemination?

Vaginal (sheep and goats), Cervical (swine), Trans-cervical (cattle and horses), and Laparoscopic.

How does Prostaglandin $F_{2\alpha}$ injection synchronize estrus in cattle?

It induces regression of the corpus luteum (luteolysis), removing the source of progesterone and bringing cows with a functional CL (days 5-18) into heat in about $3\,\text{days}$.

What is a CIDR, and how is it used in estrous synchronization?

A CIDR (Controlled Internal Drug Release) is a T-shaped nylon/silicone intravaginal device containing progesterone that blocks LH and FSH to suppress estrus; upon removal, females enter heat.

What is superovulation in embryo transfer (ET) programs?

The administration of fertility drug injections to a donor female to induce the production and release of a greater-than-normal number of eggs.

Which brain structure produces Gonadotropin-releasing hormone (GnRH), and what is its target?

GnRH is produced by neurons in the hypothalamus and targets the anterior pituitary to trigger the release of LH and FSH.

What are the source, target organs, and primary functions of Luteinizing Hormone (LH)?

Source: Anterior pituitary. Target organs: Ovary (luteal cells) and Testis (interstitial Leydig cells). Functions: Stimulates ovulation, CL formation, progesterone production, and testosterone production.

What are the source, target organs, and primary functions of Follicle-Stimulating Hormone (FSH)?

Source: Anterior pituitary. Target organs: Ovary (granulosa cells) and Testis (Sertoli cells). Functions: Stimulates follicle development, estrogen synthesis, and sperm production (spermatogenesis).

What are the three stages of follicular development before a follicle ovulates or undergoes atresia?

Recruitment (entry into gonadotropin-sensitive pool), Selection (ovulatory follicles emerge), and Dominance (final growth of ovulatory follicle and inhibition of others).

What are the three post-ovulatory ovarian structures and their features?

Corpus hemorrhagicum (blood clot formed after follicle rupture), Corpus luteum (yellow/orange transient gland secreting progesterone and oxytocin), and Corpus albicans (white fibrous scar from advanced CL regression).

How do testicular hormones regulate GnRH, LH, and FSH release in males?

Testosterone produced by Leydig cells and inhibin produced by Sertoli cells exert negative feedback on the hypothalamus to inhibit GnRH secretion and on the anterior pituitary to inhibit LH and FSH release.