REPRODUCTION

A. What is reproduction?

1. A Goal-directed Process

2. How important is reproduction to animal agriculture?

a. Right now, most producers will tell you that the problems associated with reproduction are their biggest problem:

b. Heritability estimates for reproduction traits are low (5-15%)

B. Status of Reproduction

1. Current - technology

2. Future - technology

C. Reproductive physiology is a very complicated but fascinating biological process.

1. Necessary Components

a. Female must be willing and able to accept services of the male (copulation) near a time when the egg (ovum) is released from the ovary (ovulation).

b. Male must be willing and able to service the female. He must deliver spermatozoa to the proper site in the female reproductive tract at a proper time for conception to occur. (Conception = mating or union of the male and female gametes.)

2. There are distinct anatomical and functional difference between the male and female reproductive systems:

a. Male - Development of the gamete is a continuous process resulting in an infinite number of sperm.

b. Female - Finite number of gametes. It is a cyclic process.

D. Anatomy of the MALE Reproductive System

1. Brief description and comparison of farm animals

Testis (Gonad) - primary sex organ

Scrotum -contains the testes

2. Parts of the male reproductive system and their functions

a. Testis – Fx already discussed

b. Epididymis -- duct located on the outside of the testes.

Composed of three parts - head, body & tail.

Functions are:

(1) concentrate sperm

(2) store sperm

(3) transport sperm

(4) site of sperm maturation [The entire process from the start of spermatogenesis to maturity takes ~40-60 days....depending on the farm animal species.]

c. Vas deferens -- duct which connects epididymis to urethra of

the penis. Transports sperm at the time of ejaculation.

Cut to sterilize male.

d. Common urogenital system

e. Accessory sex glands -- Secretions from these organs

constitute 50-90% of the volume of the ejaculate.

(1) Seminal vesicles - supply nutrients for the sperm

following ejaculation and deposition into the female reproductive tract. Includes carbohydrates (energy), ions (buffers) and enzymes that activate the sperm.

(2) Prostate gland - clean and lubricate the urethra ahead

of the sperm. Urine that remains has high salt content and will cause sperm to rupture and die.

(3) Bulbourethral or Cowper's gland - clean and lubricate the

urethra. Secretion is thick, viscous, and very slippery. In the boar, it produces a gelatinous material that forms a plug in the cervix of females.

f. Semen production (mature males)

	Ejaculate volume (ml)	Concentration rank
Ram	.5-2.0	1
Bull	3-10	2
Stallion	40-100	3
Boar	150-250	4
Man	2-6	5

g. Penis proper

-Organ of copulation

-Provides passageway for semen and urine

-Muscular organ characterized especially by its spongy,

erectile tissue that fills with blood under considerable pressure during periods of sexual arousal.

(1) Urethra - duct through penis that carries sperm & urine

(2) Sigmoid flexure - allows extension of penis in species

with fibro-elastic penis.

(3) Retractor penis muscle - attached to the sacral vertebra.

Relaxes during sexual excitement.

(4) Glans penis - terminal portion of penis.

Species variation of glans penis:

Bull --

Ram --

Boar --

Stallion --

[Boars and stallions deposit semen directly into the cervix; bulls and rams deposit semen into the vagina.]

3. Sperm production (spermatogenesis)

a. Seminiferous tubules -- sperm producing units of the testes.

Make up approx. 90% of the testes mass. Spermatogenesis occurs within the lumen of these long, highly-coiled structures.

b. Sertoli cells -- provide nourishment for the developing sperm.

Located within the seminiferous tubules.

c. Leydig or interstitial cells -- produce testosterone.

Located between the seminiferous tubules.

4. Sperm cell

Head - contains genetic material (chromatin) and enzymes (in the acrosome) necessary for fertilization.

Neck - attaches the head to the midpiece

Midpiece - produces energy for the sperm

Tail - propels sperm cell

Species variation

Horse - more cylindrical than bull, boar, or ram

Man - head looks like an inverted egg on neckpiece

Rat - bent or turned

Cock - very straight, long and slender

E. Reproductive Physiology of the Male

1. Brief introduction to endocrinology

a. The proper function of the cells and organs of the body is dependent on the action of hormones.

b. Hypothalamus - located within the brain.

- Integrator of most of the brain's activities.

- Produces releasing hormones (RH) which travel a short distance to the pituitary gland and cause the release of several hormones.

c. Pituitary gland (specifically, anterior pituitary)

d. General principles of feedback mechanisms

2. Hormonal interrelationships in the male

Hypothalamus - located within the brain.

* Integrator of most of the brain's activities.

* Produces a peptide called gonadotropic releasing hormone (GnRH) which controls the release of two hormones from the anterior pituitary gland called gonadotropic hormones (FSH and LH).

ˆ Stimulation by GnRH from the hypothalamus causes FSH and LH to be released from the ant. pituitary into the blood, which then go to the gonads where they stimulate specific functions.

3. Functions of reproductive hormones in the male

a. LH stimulates the Leydig cells to produce testosterone

Testosterone functions...

1) stimulates growth, development and secretory activity of accessory glands.

2) stimulates growth of the reproductive tract (at puberty)

3) initiates spermatogenesis

4) is necessary for sperm survival

5) responsible for secondary sex characteristics

-male voice

-muscle development

-crest over the neck

-libido

-whiskers in man

b. FSH - stimulates the sertoli cells to produce nutrients for the sperm.

F. What should you know about selection of herd sires?

1. Visual evaluation

2. Scrotal circumference - indicator of sperm production

3. Scrotal palpation - prominance of epididymis indicates presence of sperm.

4. Penis and prepuce observation - infection, split, rupture

5. Rectal palpation - examine accessory glands

6. Libido test

7. Semen evaluation - microscopic

G. Anatomy of the FEMALE Reproductive System

1. Parts of common urinary and genital female systems and their functions

a. External genitalia

b. Vagina -- between external genitalia and cervix

c. Cervix -- lies between vagina and uterus

d. Uterus

e. Oviduct -- long convoluted tube connecting uterine horns to infundibulum.

f. Ovaries -- paired; shape varies with species

2. Follicular growth and development

a. General information

1) Oogonia - primitive gamete of the female.

2) Hormone stimulus initiates growth and development of a new follicle. Result is the acquisition of layers of cells.

b. Primary follicle - surrounded by a single layer of cells.

c. Secondary follicle - surrounded by a double layer of cells.

d. Tertiary follicle - cells begin migration to one side leaving a cavity. Cavity is called an antrum. (Estrogen is produced by cells lining the antrum....will discuss this later.)

e. Mature or Graafian follicle - ready to ovulate. Follicle wall becoming thin. Ovum still attached to follicle wall (by cumulus oophorus...don't learn.)

f. Ovulation - follicle ruptures and ovum released. Ovum caught by infundibulum. Ovum "oozes" out; not a "bursting" action.

3. Development of the corpus luteum

a. After the ovum escapes from the mature follicle, cells of the follicle are structurally and biochemically transformed into a "yellow body" called a corpus luteum.

b. Produces hormone that maintains pregnancy (progesterone).

c. If animal does not get pregnant, CL regresses and new follicle begins to develop (following hormone stimulation).

d. In the absence of pregnancy, the corpus luteum is destroyed by a process of luteolysis. Resulting structure is a Corpus albicans - remnant of a previous CL.

H. Female Reproductive Physiology

1. Identical to the male system, ie. GnRH, LH and FSH.

GnRH = gonadotropic releasing hormone

FSH = follicle stimulating hormone

LH = luteinizing hormone

FSH + LH = gonadotropic hormones

2. FSH and LH stimulate follicular growth. Both are necessary.

3. Antrum of the growing follicle develops--->produces estrogen.

As antrum gets larger, the concentration of estrogen in the blood increases.

4. Functions of estrogen

a. Excitatory hormone in female (induces heat)

b. Stimulates growth of cells of uterus and oviduct in preparation for conception and pregnancy.

c. Coordinates events associated with sperm and egg transport.

d. Initiates duct growth and development in the mammary tissue. Lactation follows reproduction. We will think of the mammary system as having two types of tissue:

(1)

(2)

e. Secondary sex characteristics of female (feminine traits characteristic of species, site of fat deposition).

5. When the follicle is mature, a surge of LH is released...

6. Functions of progesterone

7. Compare estrous cycle to menstrual cycle.

I. Estrous cycle - series of events occurring from one heat period to the next, beginning at puberty.

Estrous = adjective

Estrus = noun; refers to "heat" or the period of time when the

female is receptive to the male.

1. Types of estrous cycles

Monestrous -

b. Polyestrous -

c. Seasonally polyestrous -

2. Behavioral signs of estrus

** a. Standing to be mounted

b. Mounting other animals

c. Social behavior - restless, gregarious activity, vocalizing

d. Frequent urination

e. Mucous discharge

3. Species comparison

Species	Estrous (days)	Estrus	Ovulation	Gestation (days)
Cow	19-23	(21) 16-20 hr	30 hr after estrus begins	283
Sow	19-23	(21) 1-3 days	30-38 hr after estrus begins	114
Mare	10-37	(21) 4-6 days	24 hr before end of estrus	336
Ewe	14-19	(17) 1-2 days	26 hr after estrus begins	147

J. Fertilization and attachment

1. Fertilization - union of male and female gametes

2. Stages of development

2-cell--> 4-cell--> 8-cell-->--> Morula--> Blastocyst--> embryo--> fetus

Developing "embryo" reaches the uterus in 3-5 days, and continues to develop.

3. Attachment of placenta to endometrium

a. Chorionic, amniotic and allantoic membranes develop around the new embryo, and the chorion attaches to the uterus.

b. Attachment begins at:

22 days in cows

15 days in ewes

13 days in sows

37 days in mares

c. Diffuse -- sow and mare

Cotyledonary -- cow & ewe

Caruncles on uterus; cotyledons on chorion

4. Parturition - termination of gestation

a. Controlled by hormones produced by both fetus & dam - initiated by fetus

- cervix dilates; pelvic ligaments relax

- uterine muscles contract, generate pressure

b. Normal presentation

- Fetuses of the cow, mare, and ewe assume positions in which the front feet are extended with the head between them.

- Fetal piglets do not orient themselves in any one direction.

c. Dystocia - abnormal or difficult labor

Factors associated with distocia:

(1) Heavy birthweight of calf is major cause in cattle. Weight of calf in relation to pelvic size is very important.

Avg. Hereford or Angus is 70 lb. Charolais, Simmental about 80-85 lb.

(2) Age of cow (heifer vs mature) plays a role due to difference in size of pelvic opening. Heifers have greater incidence of calving problems.

(3) Presentation - rump first; head or leg folded back.

K. Role of nutrition in reproductive function

1. Factors affecting reproductive performance.

a. Nutrition

b. Environment - embryonic mortality

c. Anatomical defects in reproductive tract

d. Endocrine system imbalance

e. Diseases -- (brucellosis, metritis, vibriosis, leptospirosis, trichomoniasis, IBR)

1. Over-condition (fat) - rarely observed

2. "Flushing" - Increase the level of nutrition ~2 weeks before breeding. Increases rate of ovulation in herd.

Effective for ewes and sometimes for gilts.

3. Under-condition (thin)

Biological goals of animals including man:

1. Survival

2. Reproduction

Management problem: Producers want a cow to calve every 12 mos.

365 days/yr

-283 days gestation

82 days for uterus involution & rebreeding

Most cows probably won't show estrus until after day 45 postpartum. Therefore, have only 2 estrous cycles to get them bred.

4. Recommended feeding program -

5. First-calf heifers -- Nutrition program is especially important for heifers calving for the first time.

a. Have 3 critical needs for extra nutrients:

(1) Will be lactating for the first time.

(2) Still growing.

(3) Uterine involution - preparation for another pregnancy.

b. Keep them separated from the main cow herd.

6. Replacement heifers

7. Energy is the dietary component that is usually limiting. Protein is next.

L. Strategies for optimizing reproductive efficiency

1. Artificial Insemination

History -- A.I. is not new.

b. Use of A.I. in U.S. cattle herds

c. Future of A.I.

d. Advantages of A.I.

e. Disadvantages of A.I.

1) Increased labor, management and facilities.

2) Accentuate poor genetics by using inferior sire (if unproven).

f. When to inseminate

For maximum conception, the sperm and ova must be at the site of fertilization at the peak of their fertility.

Fertile life of ovum

6-12 hr (at least 6 hr.)

Ovum is fertile 30-36 hr after onset of estrus

Fertile life of sperm

(1) Sperm survival approx. 24 hr in female tract

(2) 12 hr required for capacitation

(3) Fertility therefore limited to the last 12 hr

(4) Time for transport is approx. 5 min

g. Site of semen deposition

(1) Most anterior portion of cervix = optimum site

(2) Deposition in uterine horn has lower conception due to uterine trauma and possible infection.

(3) Second service must be mid-cervix to avoid possible abortion of an early pregnancy.

Species	Length of estrus	Ovulation	When inseminate
Ewe	1-2 days	~26 hr after onset of estrus	12-18 hr after onset of estrus
Sow	1-3 days	30-38 hr after onset of estrus	24 & 36 hr after onset of estrus
Mare	4-6 days	24-48 hr before end of estrus	? - Must palpate or use repeated breedings
Cow	16-20 hr	~30 hr after onset of estrus	12 hr after onset of estrus

2. SUPEROVULATION and EMBRYO TRANSFER

a. Hormone treatment of the female to induce multiple ovulations.

b. Multiple births.

c. Embryo transfer.

1) Advantages:

2) Disadvantages

d. Injection programs

1) Porcine FSH is most commonly used to induce superovulations in cattle.

Gonadotropins (FSH/LH comb.) have been used since 1940:

PMSG-This product contains mostly FSH activity, but has some LH.

HCG -This product contains mostly LH activity with some FSH. Used in combination with FSH or PMSG.

2) Prostaglandins are used to synchronize the estrous cycles of the donor cow and recipient cows.

(-) What are prostaglandins? They are a large group of chemically-related fatty acids. They resemble hormones in their actions, but are quite different chemically. They are produced by many tissues in the body and are ubiquitous. They cause many physiological effects, including lowering of blood pressure, stimulating contraction of smooth muscle, preventing agglutination of blood platelets, important in normal lung function, etc. There are two series: PGE and PGF. For reproduction, we will be concerned with just one - PGF_2a.

(-) Action of PGF₂a

-destroys the CL

-constricts blood flow to the ovary

e. Procedure

1) Selection -

2) Synchronization -

3) Superovulation -

4) Insemination -

5) Embryo collections & transfer -

-Flushing normally occurs 6-8 days after insemination.

-Implantation has not occurred.

-The "embryo" is in the morula stage of development.

-Embryos can be maintained in vitro for 24 hr.

-Get ~10 fertilized and unfertilized "ova". (Avg.)

f. Future - There are several concepts being researched that will greatly expand the use of ET in the future:

1) Freezing embryos -

2) Cloning and micromanipulation of embryos -

3) Sexing embryos -

COWS SHOWING HEAT AS RELATED TO BODY CONDITION AT CALVING

Condition at Calving	Days postpartum
	40	50	60	70	80	90
	---------------% showing estrus---------------
Thin	19	34	46	55	62	66
Moderate	21	45	61	79	88	92
Good	31	42	91	96	98	100

WEIGHT AT WHICH 14-15 MONTH OLD HEIFERS SHOW FIRST HEAT WEIGHT NEEDED BY

PROPORTION IN HEATANGUS	HEREFORD	CHAROLAIS	A x H	B x E
50%	550	600	700	500	650
65-70%	600	650	725	600	700
85-90%	650	700	750	650	750

B x E = British breed x Exotic breed cross