ANSC 107 Reproduction

Dr Ramsey TAMU

Genotype

Animal’s blueprint

Chromosome

Large molecule containing DNA; made of genes.

Gene

Segment of chromosome composed of DNA.

DNA

Two strands of sugar phosphate backbone with bridges of nitrogen bases.

Nucleotide

Sugar, phosphate, and one of the 4 nitrogen bases.

Expression of genes =

Money

Inheritance

Passing traits from parent to offspring.

Alleles

Alternate forms of a gene that affect the same trait.

Homozygous

AA/aa

Heterozygous

Aa

Gametes

Reproductive cells, carry for half of the parent’s genetic code.

Codominance

Both alleles expressed.

Incomplete dominance

Heterozygotes appear as intermediate, no dominance.

Sex-influenced

Phenotype expressed differently between sexes.

In males, horns are…

Dominant

In males, polled is…

Recessive

In females, horns are…

Recessive

In females, polled is…

Dominant

Sex-limited

Traits unique to one sex

• both carry but only one is capable of expressing.

Milk production is…

Carried by both, only expressed by females.

Sex-linked

Genes found only on X or Y chromosome.

Males are…

XY

Females are…

XX

Majority of sex-linked traits are…

X linked

Recessive X linked conditions are more commonly expressed in…

Males because they only have one X chromosome.

Y linked traits only occur in…

Males

Selection

Determining which individuals reproduce.

• Artificial and natural

• We use artificial more.

Natural Selection

Based on suitability and opportunity..

Natural Selection - Suitability

Injured or weak animals are less likely to reproduce.

Natural Selection - Opportunity

Exposure to more potential males (geography or aggression)

• Increases likelihood for reproduction.

Artificial Selection - Management

Decisions to regulate opportunity.

• Culling, castrating, specified mating.

Qualitative Traits

• Classified into groups

• Visible

• Controlled by few genes

Quantitative

• Numerically measured

• Requires instrument

• Controlled by many genes

• Additive in nature

Heritability (h²)

Impact of additive genes

• Variation in phenotype from parent to offspring (proportion or percentage; 0-1), 1 happens to pass.

• Greater the value, more likely traits to be passed.

• Differs with each group of animals/operation.

• Indicates potential genetic progress with each generation.

Factors in Calculating Heritability - Selection Differential

• Mean advantage of parents over mean value of population.

• **Litter size of 11 when mean is 7 = differential of 4.

Factors in Calculating Heritability - Highly heritable traits

• (0.4-0.6)

• Ex: carcass merit traits

Factors in Calculating Heritability - Moderately heritable traits

• (0.2-0.4)

• Ex: growth traits

Factors in Calculating Heritability - Lowly heritable trait

• (0-0.2)

• Ex: reproductive traits

• **Litter size is 0.1=10% of the 4 pig selection differential would be inherited so 0.4 pigs more = litter size increases from 7 to 7.4 pigs per litter.

Inbreeding

Mating closely related individuals.

• Increases homozygous gene pairs

• Decreases variation

• Decreases vigor and production

• Increases expression of potentially detrimental recessive genes.

Spider Lamb

An autosomal recessive condition, causes skeletal and cartilage deformities.

• Seen in black-faced breeds like the Suffolk and Hampshire.

• Both parents must carry.

Curly Calf Syndrome

A lethal genetic defect that causes a bent or twisted spine.

• Autosomal recessive.

• Both parents must carry.

• Seen in Angus.

Porcine Stress Syndrome

An inherited genetic defect in pigs where normal stressors cause their muscles to lock up, leading to a sudden, fatal spike in body temperature.

• Autosomal recessive neuromuscular disorder.

• Seen in Pietrain.

Hyperkalemic Periodic Paralysis

Genetic disorder that causes muscle weakness, stiffness, or temporary paralysis.

• Autosomal dominant.

Dwarf Gene

Smaller and thicker, two carriers and offspring express.

Linebreeding

Form of inbreeding, using repeated crossings to ancestors.

• Maintain influence of outstanding ancestor(s).

• Ancestor(s) typically appears multiple times on both sides of pedigree.

Outbreeding

Mating less closely related animals than the general population.

• Can include crossing with a breed or between breeds.

• Increases heterosis.

• Increases hybrid vigor and performance.

Crossbreeding

To use complementarity of traits.

• The mating of two individuals from different breeds.

• Goal: Offspring to outperform.

• All crossbred are outbred, not all outbred are crossbred.

Muscling and marbling are…

Highly heritable

EPDs ______ be compared across breeds,

cannot

Breeding Value

Estimated value of an individual as a parent.

• Based on performance of individual and close relatives.

EPD

Expected Progeny Difference

• Half of breeding value allows us to compare.

• Useful for comparison within breed or group.

EPDs -Traits

• Birth: weight, type, gestation length. (Birth weight is critical)

• Growth: weight at and/or time to benchmarks, frame size.

• Maternal: milk production.

• Terminal: carcass merit.

• Reproduction: scrotal circumference (puberty), litter size.

• Behavior: maternal instinct, docility, speed, agility.

EPD : High accuracy

>0.7

EPD : Low Accuracy

<0.4

Accuracy increases with…

More information

Testes

Primary male gonad, produces sperm and testosterone.

Epididymis

Tightly coiled tube attached to the testis.

• Sperm matures here and is stored until ejaculation.

Caput Epididymis

Head of the epididymis

• Maturation of spermatozoa

• Fluid absorption

• Not capable of fertilization or motility

Corpus Epididymis

Body of the epididymis

• Maturation of spermatozoa

• Sperm gains a little bit of motility.

Cauda Epididymis

Tail of the epididymis

• Final maturation

• Long storage until ejaculation

• Sperm is fertile and mobile

Vas Deferens

Carries mature sperm upward out of the scrotum and into the pelvic cavity.

• During ejaculation

• Long, muscular tube

Tunica Albuginea

Connective tissue that holds testes together.

• White and tough

Seminiferous Tubule

Spermatogenesis

• True germinal epithelium

• Locates in testes

Rete Testis

Transport sperm cells out of the seminiferous tubules.

• Collecting point.

• ~100 tubules

Efferent Ducts

6-12 tubules absorb fluid.

The middle of the testis

The mediastinum.

• Transports spermatozoa out.

Stallions have what type of penis?

Vascular

• Erection from blood flow

Fibroelastic Penis

Does not expand, it expands.

• Expands through sigmoid flexure and retractor muscle

• All animals except horses

Vascular Penis

Increases in diameter because of blood flow.

• Horses and humans.

• Changes shape of glans. It looks like a bell and aligns with the cervix. (flares at bottom)

Glans

Tip of penis. (differs depending on species)

Why don’t castrated males have a good reproductive system?

Because of decreased testosterone.

4 Accessory Glands

• Seminal Vesicles

• Prostate Gland

• Cowper’s Glands

• Filiform Appendage

Filiform Appendage

Thin extension at glans of penis.

• Sprays semen evenly across cervix during ejaculation.

• Found in small ruminants.

Prostate Gland

Secretes fluid into the pelvic urethra to cleanse/neutralize urine residue.

• Optimizes condition for sperm survival.

Seminal Vesicles

Produces majority of seminal fluid volume, provides energy (fructose), and buffering agents for sperm.

Cowper’s Glands

• Produces pre-ejaculatory fluid.

• Lubricates the urethra prior to arrival of semen.

Spermatogenesis

Production and supply of sperm.

• Takes 60 days.

• If animal is sick, it interrupts and makes them restart.

Overall functions of males

• Spermatogenesis

• Detect females in estrus using visual cues.

• Inseminate females and fertilize the female gamete.

Spermatic Cord

• Vas Deferens

• External Cremaster Muscle

• Tunica Albuginea

External Cremaster Muscle

Contracts of relaxes to raise or lower the testes.

• Maintains proper temperature.

#1 Purpose of the male reproduction system

Spermatogenesis

Where does spermatogenesis start?

In the seminiferous tubules.

• All the tubules stack around core.

Scrotum

Exterior skin, protection, regulates temperature.

• Spermatozoa needs to be in a temperature regulated environment in order to be produced.

• 4^o-6^o cooler than body temperature.

• Temperature needs to be regulated by sweating → evaporative cooling.

In scrotal skin there are…

Thermo sensitive neurons.

• Reacts to ambient temperature, sends signals to nervous system to alter behavior.

  • Pants, release excess heat.

  • Shivers, increases body temperature.

  • Can constrict scrotum, push testes closer to body.

In between scrotal skin and tunica albuginea, there’s…

Fat (white coating) that helps with temperature regulation.

The testes produces…

Sperm and testosterone

Leydig cells

Produces testosterone, in the lobules of the testis.

The Basement Membranes

Surrounds the seminiferous tubules, separates them.

• Protects the tubules from blood vessels on outside.

• Want testosterone in blood stream, not spermatozoa, that’s why separated

Sertoli Cells

Located within seminiferous tubules

• Supports spermatogenesis.

• Spermatozoa are produced within the seminiferous tubules.

• Germinal cells (outer edge) → spermatocytes → spermatids (flagella)

  • Meet at middle of seminiferous tubules (mitosis and meiosis).

  • Takes 16 days

In order to become a spermatocyte, what must occur?

Spermatogonia must undergo mitsosis.

In order to become a spermatid, what must occur?

Spermatocytes must go through Meiosis 1 and 2.

Differentiation

No more cell divisions, spermatids are spermeated into the lumen.

Once past bladder…

The vas deferens becomes the urethra.

Sigmoid Flexure

S shaped part of fibroelastic penis.

• Held together by retractor muscles.

• Stimulation → relax → straighten out.

Flehmen Response

• Exposure of nasopalatine duct to absorb pheromones.

• Upper lip curls, scenting to detect estrus.

Cues in Stimulation

• Visual

• Auditory

• Tactile

BSE

Breeding Soundness Evaluation

• Palpate testes, make sure that the epididymis is healthy

Epididymitis

Inflammation of the epididymis.

Which specie has the smallest ejaculate volume?

Sheep

• Little flap makes it harder for sperm to get through.

Which specie has the largest ejaculate volume?

Swine

• Takes longer to fertilize