Animal Science Exam 4

Breeding & Genetics & Reproduction

DNA sequence on the chromosome biological important molecule

Gene

alternative forms of a gene (Bb, bb, BB)

Alleles

all the genetic information or hereditary material possessed by an organism

-genes are ordered sequences

Genome

alleles present at a loci (BB, Bb, bb)

Genotype

the expresses characteristics

-P=G+E (environment)

-color, horned vs. polled, birth wights

Phenotype

▪Primarily determined by genotype

▪Little or no influence on environmental influence

▪Determined/controlled by a # of genes

▪Often detected by the visual observation

▪Examples:  hair color, horns

Simply Inhereited Traits

Most traits of economic importance

Affected by many genetics

environment affects gene expression

▪Can measure phenotype, but cannot determine the specific genotype at all genes/ loci affecting phenotype

▪Examples:

•Weights

•Milk production

•Fertility

Performance-ADG, Efficiency, Speed

Polygenetic Traits

Known: effects which have a average effect on all individuals within a specific category

ex age, age of cow and gender

ex weaning weight

calves born earlier in the calving season are older at weaning and will be heavier at weaning

▪Unknown:  random in nature

Eviromental Effects on Traits

adjust records to remove environmental affect

Ex:) weaning weight of calves (adj: age of calf, sex) (adj to a common age 205d)

Environmental Adjustment on traits

Mean=the average

Standard Deviation - represents a measure of variation

Normal Distribution

•+ 1 SD = 68% of the population

•+ 2 SD = 95% of the population

•+ 3 SD = 99% of the population

Standard Deviation of populations

Important tool for genetic improvement

Selection

•prevent some from reproducing

•use others to become parents of many offspring▪

Change gene frequency in the population

•increase frequency of desirable genes (alleles)

•decrease frequency of undesirable genes

Selection (part 2)

Differential Reproduction

proper selection of phenotype will change genotype of population over time

Selection is based on..

% of the phenotypic variation that is genetic and transmitted from parents to progeny

Ranges 0-100%
Is a estimate

Heritability

Heritability

selection Differential

Exprected progress from Selection-Factors affecting progress

Differences between the trait mean of the selected animals and the average value for the group which they were selected

Selection Differential

“Phenotype * h²”

ex litter size in pigs: 2(Phenotype # of pigs more than average) × 0.09(heritability of the litter size)=0.18

Breeding value can be estimated by

average age of parents (when offspring born are born)

Generation Interval

1-1.5 years

Generation Interval Average Values-Chickens:

1.5-2 Years

Generation Interval Average Values-Swine:

3-5 years

Generation Interval Average Values-Sheep:

4-6 years

Generation Interval Average Values-Dairy Cattle:

also 4-6 years

Generation Interval Average Values-Beef Cattle:

8-12 years

Generation Interval Average Values-Horses:

Heritability

selection Differential

Generation Interval

Genetic Variation

Affects of Genetic Change Per Year

½ of parents genes are transmitted = ½ breeding value

▪the amount by which the …. Average progeny of the animal is expected to different from the average of the herd or population. the average of the herd or population.

Expected Progeny Difference

good tool for genetic selection

used to compare genetic potential-cattle sheep and swine

base = 0

EPDS

Multiple Trait selection slows change, more desirable

risks-too much progress in one trat may lower productivity in other traits

also traits may be theoretically correlated

some of same genes affect more than one trait

Genetic Change & Selection Methods

Set minimum levels for each trait of importance

relatively common

work with small number of importance traits

Disadvantages-may cull a relatively superior animals for poor performance in a single trait

Methods of Selection—Independent Culling Levels

Recognizes value of multiple traits

economically weights value of different traits

Provides overall ranking from best to worst

Most Effective

Most difficult to develop

Selection Index

Depends on breed association ex: feedlot value, grid value, Beef value.

Selection Index-Cattle Examples

heritable traits

ease of measurements

associated with economic vale

accurate genetic estimates

available genetic variation

Requirements of Effective Selection

Yes, combination-of genetic selection and improved environment

Turkeys: wild- 10lbs in 6 M

Modern- 30lbs in 5M

Does Selection Work?

Genetic Abnormalities

Dwarfism

Tibial Hemimilia

Ectodermal dysplasia

Carcass quantity and yield

DNA Testing-Potential Benefits

Traits without routine performance data (disease resistance, fertility)

Traits that are more evident late in life (cows stays in herd)

Post-selection traits (carcass quantity and palpability) (and yield)

DNA Testing-Benefits

Marbling

environmental factors: time of feed, age, stress, implant system.

Limiting factors for DNA testing

Genomically enhanced EPDs used in most seedstock industries

EPD data

Costs (polygenetic test 20-50 per test)(parent matching 15-25)

DNA Testing- Disadvantages

Breed complementation- match strengths & weaknesses of different breeds

Heterosis (hybrid)-increase in productivity of the crossbred progeny that is greater than expected based on the average of the parents performance.

Why crossbreed?

1.)Terminal-

all progeny are marketed(sold) to produce meat

buy replacement breeding stock

use a performance/ carcass oriented sire breeds

2.)Rotational Crossbreeding(2 or 3 breeds)

crossbred females use to produce new generation

Reproductive heterosis= high (maternal)

Heteroses increases as the # of breeds in cross increase

Crossbreeding Programs

Two breed rotation

females sired by breed A are mated to breed B sires and vice-versa.

Rotational Programs

Science that pertains to the function of organs and organ systems

Physiology and Reproduction

study of the function of the reproductive systems

Reproductive Physiology

Trait of greatist economic importance

Cattle: cost of a open cow

cost of lost calf:1450

maintain:$260-$350

Swine:100-175 a pig

Lost market value for the litter:$400-$700

Horses: Have stud fees from the “champion”

Fertility & Reproductive Rate

They produce quantities of semen

-Sperm cells and Seminal fluids

Find the receptive female

-must have the desire

Mount and serve

-must have to mare and & deliver semen

Reproduction: Males Role

Testicles(2)

-produce sperm cells to fertilize the ovaries

-produce the hormone Testosterone

-masculine appearance & behavior

-stimulates sperm production

-growth

Male Reproductive Organs and Function

Epididymis

-concentration of spermatozoa

-storage of maturation site

Male Reproductive Organs and Function (2)

Scrotum

-Provides support for testicles

-Temp regulation for sperm livability (5-10 below body temp)

Male Reproductive Organs and Function (3)

Section tool used for reproductive management

-used primary in cattle but applicable to all

Good indicator of: age @ puberty/ overall fertility

easy to measure and retable, highly heritable

“the larger the better”

12-14m of age want >32cm

Scrotal Circumference

transportation tube that carries sperm from the epididymis to the urethra

Vas Deferens

larger canal from urinary bladder extending the full length of the penis

Urethra

produce fluids: add volume and nutrients

accessory sex glands

organ of copulation

Penis

engorgement with blood

aids copulation

shuts off bladder flow

erections

develop and release the egg

permit mating(estrus/standing heat)

conception

develop the embryo

nourish the fetus

parturition-birth

Lactation-milk production

Rebreeding

Reproduction: Female's Role

produce the ova(sex cells or eggs)

Female Reproductive Organs and Function-Ovaries

Site of fertilization

transport of eggs to the uterus

Female Reproductive Organs and Function-Oviducts

Site of pregnancy

responsible for expulsion of the fetus (birth)

through muscular contractions

shape of the uterus is species specific

Female Reproductive Organs and Function-Uterus