Animal Science Lecture Final Review

Gestation

Process of carrying or being carried in the womb between conception and birth (pregnancy)

Parturition

The action of giving birth to young

Estrus

(Heat) Recurring period of sexual receptivity and fertility in many female mammals

Dam

Female parent

Sire

Male parent

Body Condition Score

A practical method of assessing an animal’s body fat by eye and touch

What is the critical score for BCS?

Between 4 and 5

(4 and under is bad, 5 and above is good)

During which trimester of pregnancy is the most weight gain

Third

Conception rate for a BCS 4 or under

19%

Conception rate for a BCS 5 and above

75%

Polygamy

One sire to many females

85 degrees F

Stress temperature for cattle

How does heat affect estrus?

Estrus can become shorter and less obvious

Monozygotic Twins

• Genetically and physically identical

• One fertilized egg splits into two identical halves during early embryonic stages

Dizygotic Twins

• Fraternal

• Formed from two completley different ova at the same time

Freemartin

Condition that can cause infertility in a female twin that also has a male twin

Broad Ligament

• Suspends the female reproductive organs

• Contains arteries, veins, and nerves

Ovaries

• Primary female reproductive organ

• Analogous to the testicles

• Produce the female gamete ovum (egg)

• Produces female sex hormones (estrogen and progesterone)

Monotocous

One egg is released and fertilized (e.g. cattle)

Polytocous

Multiple follicles ruptured and fertilized (e.g. pigs)

Medulla

Receives the blood

Cortex

Contains the ova, where Graafian follicles develop, estrogen is produced, Cl develops, and produces progesterone

Primary Follicle

Surrounded by a single layer of follicular cells

Secondary follicle

Primary layer has multiplied into two layers

Tertiary “growing” follicle

Begins to form the antrum

Graafian follicle

Mature follicle appears as a blister, if ovulation does not occur the follicle will be broken down

Antrum

Cavity containing follicular fluid

Corpus Hemorrhagicum

• Forms subsequent to ovulation to the follicle

• Blood clot fills the cavity

• Similar to a bruise

• Collapsed follicle contains blood, lymph, granulosa, and theca cells

Corpus Luteum

• Solid tissue which is composed of luteal cells that originate from granulosa and theca cells of the Graafian Follicle

• Produces progesterone

Corpus Albicans

• Connective tissue replaces the luteal cells (white)

• Continues to get smaller with each day until they are not visible and process repeats

What do luteal cells produce?

Progesterone

What are the stages of follicle growth?

1. Primary Follicle

2. Secondary Follicle

3. Tertiary Follicle

4. Graaphian Follicle

5. Coprus Hemorrhagicum

6. Corpus Luteum

7. Corpus Albians

Oviduct

• Paired, coiled tubes (fallopian tubes)

• Spans from near the ovary to the tip of the uterine horn

• Transports the gamete and is the location of fertilization

Is the oviduct tissue designed to support pregnancy?

No

What are the segments of the oviduct?

• Infundibulum - funnel shaped opening near the ovary that picks up the egg at ovulation (“catcher’s mitt”)

• Ampulla “neck” - ampullary isthmic junction is the specific site of fertilization

• Isthmus - joins the uterus at the tubo-uterine junction

Uterus

• Houses the fetus

• Two horns with one common body

• Extends from the tubo-uterine junction to the cervix

Carnucles

Button-like projections in the uterus that allow for nutrient flow to the fetus

Where do we want implantation to occur?

The uterus

Placentome

The specialized area of attachment between the fetal placental cotyledon and the maternal uterine caruncle

Which uterine classification is this?

• Simplex

• Primates & Humans

Which uterine classification is this?

• Bicornuate (sow)

• Horses, Sheep, and Swine

Which uterine classification is this?

• Bicornuate (cow)

• Cattle, Horses, Sheep

Which uterine classification is this?

• Duplex

• Rodents and Rabbits

Which uterine classification is this?

• Bipartite

• Deer, Moose, Elk, and Cats

Cervix

• Prevents contamination of the uterus and protects the fetus (cervical plug)

• Thick walled tube (inelastic)

• Posterior protrudes into the vagina

Fornix or “blind pouch”

• Fold created by protrusion of the cervix into the vagina

• Issue for A.I.

Which classification of cervix is this?

• Annular Rings

• Ewe and cow

Which classification of cervix is this?

• Longitudinal Folds

• Horses

Which classification of cervix is this?

• Corkscrew

• Swine

• Matches boar’s spiral shaped penis

Vagina

• Serves as the organ of copulation and the birth canal

• Thin-walled tube (elastic)

• Anterior vagina - location of semen disposition by the bull and ram

Vulva

External entrance to the reproductive organs

Clitoris

• Analogous to the penis

• Stimulates hormone release

Is the oviduct where fertilization or implantation takes place?

Fertilization

Testes

• Primary organs of male reproduction

• Analogous to the ovary

• Produces the male gametes (sperm)

• Produces the male sex hormone (testosterone)

Seminiferous Tubules

Produces the sperm cells in the testes

Sertoli cells

Line the seminiferous tubules and under the influence of FSH, nurture the developing sperm cells (testes)

Leydig cells

In the testes, sit across the blood-testes barrier from the Sertoli cells and produce testosterone, under the influence of LH, to aid in development of sperm cells

What temperature should be maintained to control testes?

5 degrees C below the body temp

Cryptorchid

One or both testes retained in the body cavity

Mechanisms for temperature regulation in the testes

• Scrotal skin will wrinkle when the dartos muscle contracts

• Cremaster muscle can pull the testes closer to the body

• Pampiniform plexus is a network of blood vessels that will cool the blood going to the testicles

• Thermoregulation by muscles

Rete Testes

Tubules that transport the spermatids from the seminiferous tubules to the epididymal duct

Epididymis

• Aids in the maturation of the sperm and serves as storage until needed

• 3 segments

  • Head (caput) - maturation and concentration

  • Body (corpus) - maturation and concentration

  • Tail (cauda) - storage area for mature sperm

• Located on the long axis of each testes

Deferent Duct (Vas Deferens)

Transports sperm from the epididymis to the pelvic urethra in preparation for ejaculation

Where we see vasectomies

Spermatic Cord

Composed of the deferent duct, blood vessels, and nerves (that support the testes) and the Cremaster muscle

Accessory Glands

• Adds fluid portion of the semen (seminal plasma)

  • Vesicular

  • Prostate

  • Bulbourethral

Vesicular Glands (Seminal Vesicles)

Provide nutrients and buffering capacity to the semen

Prostate Gland

Produces thin, watery fluid to cleanse the urethra prior to ejaculation (urine is very detrimental to sperm)

Bulbourethral Glands (Cowper’s Glands)

Produce the gel portion of the semen and help force the semen from the urethra at ejaculation

Pelvic Urethra

Passageway for semen and urine

Penis

Organ of copulation

Glans Penis

Terminating end of the penis

Vascular type penis

Erectile tissue which engorges with blood to achieve erection

Fibroeleastic type penis

The retractor penis muscle relaxes to allow the rigid penis to extend from the prepuce, then contracts to pull the penis to the prepuce

Sheath

Outer skin containing hair and wool follicles

Bull Penis

Very rapid copulation with low volume and high concentration

Ram Penis

Has a filiform appendage (hair like projection) at the end of the glans penis, which sprays semen around the cervical opening. Rapid copulation, very low volume, and high concentration

Boar Penis

Has corkscrew shaped glans penis, long copulation, high volume, and low concentration

Stallion Penis

Moderate copulation time with high volume and relatively low concentration

Copulation

Gonadotropin-Released Hormone (GnRH)

• Peptide hormone produced and released by the hypothalamus

• Controls the release of FSH and LH from the anterior pituitary

Follicle Stimulating Hormone (FSH)

• Peptide hormone produced and released by the anterior pituitary in response to GnRH

• Female: Acts on the ovary to stimulate growth and development of follicles

• Male: Acts on the Sertoli cells to stimulate sperm cell production

• Works toward gamete production in each sex

Luteinizing Hormone (LH)

• Peptide hormone produced and released by the anterior pituitary in response to GnRH

• Female: Acts on the follicle to cause ovulation and subsequent formation of luteal cells that form the CL. Induces continued production of progesterone from CL

• Male: Acts on the Leydig cells to induce production of testosterone

Progesterone

• Steroid hormone produced by the corpus luteum

• Prepares uterus to receive the embryo and maintains pregnancy

• Responsible for the quiescence of the system during diestrus

• Only found in females

Estrogen / Estradiol

• Female: Steroid hormone produced by the developing and mature follicle

  • Responsible for the development of secondary sex characteristics during puberty

  • Relaxes the cervix during estrus

  • Responsible for behavioral signs of estrus

• Male: Function not well understood, especially high in the stallion. Produced in testes.

Prostaglandin (PGF 2a)

• Lipid hormone produced by the uterus in females

• Causes regression of the corpus luteum if no pregnancy occurs

• Causes uterine contractions at parturition or for cleansing of the uterus

Proestrus

• Days17-21

• Follicular growth, corpus luteum regression

Estrus

• 6-30 hours

• Sexual receptivity

• Growth and maturity of graaphian follicle (ovulation)

Metestrus

• Days 1-3

• Corpus luteum commences development

Diestrus

• Days 4-16

• Luteal development (progesterone)

Testosterone

• Steroid hormone produced by the Leydig cells in the testes

• Responsible for secondary sex characteristics in males

• Males’ sexual behavior or libido

• Maturation of sperm

Oxytocin

• Produced by the hypothalamus and stored in the posterior pituitary

• Released in response to stimulation of the mammary system to induce milk letdown

• Released during parturition to cause uterine contractions to aid in fetal and placental expulsion

• May also be released by the luteal cells in some species

Artificial Insemination

Semen is deposited in the female reproductive tract by artificial techniques rather than natural mating

Seminiferous Tubule

Tube #1

Rete Teste

Tube #2

Epididymis

Tube #3

80-90%

% AI in Dairy Cattle

Less than 5%

% AI in Sheep

95%

% AI in Turkeys

• Genetic improvement through increased use of superior sires

• Disease control (especially STD)

• May be more economical

• Improved record keeping

• Eliminates need to keep bulls on farm

Major Advantages of AI

• Time required for estrus detection

• % of cows in estrus during breeding season

• Trained personnel required

• Can accentuate poor sires

Major Disadvantages of AI