Download Animal Breeding/Genetics For

Animal
Breeding/Genetics
For:
ADVS 1110
Introduction to Animal Science
Genetics
Only partially responsible animal
performance.
Animal Performance/Production
• Genetics
• Environment
– Nutrition
– Housing
– Disease events
– Management practices
Components of
Animal Husbandry
Content Topics:
• Basics of Genetics
• Selection
• Applied Animal Breeding
Basics of Genetics
Basics of Genetics
• Genetics – science of heredity
• Heredity – the hereditary transmission of
genetic or physical traits of parents to
offspring.
Basics of Genetics
• Gregor Johann Mendel,
1822-1884
– An Austrian Monk and
Botanist, “founder of
modern genetics”.
– Mendel conducted basic
breeding experiments with
garden peas between 1857
and 1865, during the time
of the U.S. Civil War.
Basics of Genetics
• Mendel in his monastery at Brunn
(now Brno, in Czechoslovakia),
applied a powerful curiosity and a
clear mind to reveal some of the
basic principles of hereditary
transmission.
• In 1866, he published in the
proceedings of a local scientific
society a report covering eight
years of his studies, but for 34
years his findings went unheralded
and ignored.
Basics of Genetics
• Finally, in 1900, sixteen (16) years after
Mendel’s death, three (3) European biologists
independently duplicated his findings, and this
led to the dusting off of the original paper
published by the Monk thirty-four (34) years
earlier.
Basics of Genetics
• “Mendelian” inherited according to Mendel’s
laws.
• “Mendelism” – the theory of heredity as
formulated by Gregor Mendel.
Basics of Genetics
Basics of Genetics
• Mendel’s basic phenotypes with his pea
studies:
Basics of Genetics
Basics of Genetics
Basics of Genetics
Mendel’s Laws – The four (4) principles of
hereditary phenomena discovered and
formulated by Gregor Mendel:
Basics of Genetics
1. The Law of Independent Unit
Characters
2. The Law of Segregation
3. The Law of Dominance
4. The Law of Independent Assortment
Basics of Genetics
1. THE LAW OF INDEPENDENT UNIT
CHARACTERS: characteristics such as
height, color, etc., are inherited
separately as units.
Basics of Genetics
2. THE LAW OF SEGREGATION: body
cells and primordial germ cells contain
pairs of unit characters, and when
gametes are produced, each gamete
receives only one member of each pair.
Basics of Genetics
3. THE LAW OF DOMINANCE: in every
individual there is a pair of determining
factors (genes) for each unit character,
one from each parent, if these factors are
different (heterozygous), one character
(the dominant) appears in the organism,
the other (recessive) being latent; the
recessive character can appear in the
organism only when the dominant is
absent.
Basics of Genetics
4. THE LAW OF INDEPENDENT
ASSORTMENT: any one pair of
characters is inherited independently,
notwithstanding the simultaneous
transmission of other traits. (This
principle has been modified by the
discovery of linkage and pleiotrophy.)
Basics of Genetics
• Robert Bakewell of Dishley,
Leicestershire, England, 1726-1795, found
and “Father of Animal Breeding”.
Basics of Genetics
• Bakewell was an English farmer of
remarkable sagacity and hard, common
sense.
• He was the fist great improver of cattle in
England.
Basics of Genetics
• Bakewell’s objective was to breed cattle
that would yield the greatest quantity of
good beef rather than to obtain great size.
Basics of Genetics
• Bakewell’s efforts with cattle were directed
toward the perfection of the English
Longhorn, a class of cattle common to
the Tees River area.
Basics of Genetics
• Bakewell also contributed significantly to
the improvement of the Leiceister breed
of sheep, and the Shire horse.
Basics of Genetics
• Bakewell established the Dishley Society
to ensure the purity of livestock breeds.
• The Dishley Society was organized in the
Leicester Secular Hall.
Basics of Genetics
Careful analysis of Bakewell’s methods
reveals that three (3) factors were
paramount to sound animal breeding:
1. Establish A Definite Goal
2. Breeding the Best to the Best
3. Use Proven Sires
Basics of Genetics
• Genes:
– Genes normally occur in pairs in each body
(non-germ) cell of individual organisms, such
as our farm animals.
– Genes are located on or in distinct ‘rod’
shaped bodies called Chromosomes.
Basics of Genetics
• Chromosomes:
– Chromosomes are carried in the center or
nucleus of each cell.
– Chromosomes occur in sets of two.
– Each set is usually identical.
– The number of chromosomes in each body
cell of all members of a specie is normally the
same.
– All of our farm animals are normally Diploid
(sets of 2), aka 2n.
Basics of Genetics
• Germ Cells, Sex Cells or Gametes:
• Gametes:
– Female = Ova or ovum
– Male = Spermatozoa or sperm cell
– Contain only 1 member of the hereditary
factors, and referred to as Haploid, aka 1n.
– Haploid refers to one half of the Diploid
number of Chromosomes for a given specie,
as found in the germ cells or gametes.
Basics of Genetics
• Alleles:
– Genes are paired in each animal, and each
kind of gene has a particular chromosome
location (loci or locus) and is called an
Allele.
– Alleles are two (2) genes that occupy the
same (locus) on Homologous
Chromosomes and affect the same trait.
Basics of Genetics
• Alleles (continued):
– Homozygotes are Homozygous(same
alleles) – TT or tt
– Heterozygotes are Heterozygous(different
alleles) – Tt
– TT, Tt, and tt are genetic allelic pairs that
express the “tall” (T) or “short” (t) traits in pea
plants; also called Genotypes found in cells.
– Tall or Short are Phenotypes or outward
appearances of pea plant traits.
Basics of Genetics
• Gametogenesis and/or Gamete Formation:
– Meiosis, aka Reduction Division - Takes place
in the Gametogenic process.
– Zygote – New individual genetic organism.
– Chance – When more than one kind of Gamete is
produced by reproducing parents, ‘Chance’
determines according to the “Laws of
Probability”, which Gametes will unite to produce
the new individual organism(s) (Zygotes).
Basics of Genetics
• Mitosis:
– The process of division of body cells.
– This regular process keeps the number of
Chromosomes constant in body cells
throughout the organism.
– When body cells divide this is the process by
which tissue growth and renewal is
accomplished.
– Each Chromosome is normally duplicated
exactly along it’s entire length.
Basics of Genetics
• Meiosis:
– Meiosis means to make smaller.
– Meiosis is a form of cell division that reduces
Chromosome numbers from Diploid (2n) to
Haploid (1n).
– Meiosis occurs in the formation of Sex Cells
(Gametes) or Spermatozoa or Ova (Ovum).
Basics of Genetics
• Sex Determination:
– Mammals
– Avian Species
Basics of Genetics
• Sex of an Ova (egg) and Sperm united
are referred to as a Zygote, and is
determined by the kind of Sperm it unites
with at Fertilization.
Basics of Genetics
• Sex Determination:
• Sex Chromosomes – Mammals:
– Female Mammals = XX
– Male Mammals = XY
– The Sex Chromosomes are carried by the
Gametes (Sex Cells; sperm & ova).
Basics of Genetics
• Sex Determination:
• Sex Chromosomes – Mammals:
– Female Mammals produce only one kind of
egg, those containing an “X” Chromosome.
– Male Mammals produce two (2) kinds of
Sperm, those containing an “X”
Chromosome and those containing a “Y”
Chromosome.
Basics of Genetics
• Sex Determination:
• Sex Chromosomes – Mammals:
• In Mammals then:
– Females are Homogametic.
– Males are Heterogametic.
Basics of Genetics
• Sex Determination:
• Sex Chromosomes – Avian Species
(birds):
– Female Avians = ZW
– Male Avians = ZZ
– The Sex Chromosomes are carried by the
Gametes (Sex Cells; sperm & ova).
Basics of Genetics
• Sex Determination:
• Sex Chromosomes – Avian Species
(birds):
– To avoid confusion, the Sex
Chromosomes in birds are usually referred
to as “Z” and “W” Chromosomes.
– In Avians then:
• Females are Heterogametic.
• Males are Homogametic.
Basics of Genetics
Genetic Composition of Various Animal Species:
Diploid (2n)
Haploid (1n)
Cattle
60
30
Swine
38
19
Sheep
54
27
Goat
60
30
Horse
64
32
Animal Specie
Basics of Genetics
Genetic Composition of Various Animal Species:
Diploid (2n)
Haploid (1n)
Mouse
40
20
Rat
42
21
Human
46
23
Cat
38
19
Dog
78
39
Animal Specie
Basics of Genetics
Genetic Composition of Various Animal Species:
Diploid (2n)
Haploid (1n)
Duck
80
40
Turkey
80
40
Chicken
78
39
Rabbit
44
22
Donkey
62
31
Bison
60
30
Animal Specie
Basics of Genetics
• Modes of Inheritance:
– Dominant
– Recessive
– Incomplete Dominance, aka “Blending”
– Sex-Linked
– Epistasis, aka “Overdominance”
– Semi-lethal Factors
– Lethal Factors
Basics of Genetics
Examples of Dominant and Recessive Traits in Farm
Animals
Specie
Dominant Trait
Recessive Trait
Cattle
Black Hair Coat
Red Hair Coat
Cloven Hooves
Mulefoot
Normal Muscling Double Muscling
Normal Size
Dwarfism
Polled
Horns
Basics of Genetics
Examples of Dominant and Recessive Traits in Farm
Animals
Specie
Dominant Trait
Recessive Trait
Horses
Bay
Non-Bay (Black)
Black Hair Coat
Chestnut or
Sorrel
Curley Hair
Normal Hair
Poultry
Barred Plumage
Broodiness
Non-Barred
Plumage
Non-Broodiness
Basics of Genetics
Examples of Dominant and Recessive Traits in Farm
Animals
Specie
Dominant Trait
Recessive Trait
Poultry
Sheep
Feathered
Shanks
White Skin
Clean Shanks
Wooly Fleece
Hairy Fleece
White Wool
(except for
Karakul and
Black Welsh)
Black Wool
Yellow Skin
Basics of Genetics
Examples of Dominant and Recessive Traits in Farm
Animals
Specie
Dominant Trait
Recessive Trait
Swine
Black Hair
(Hampshire)
Cloven Hoof
Red Hair
Mulefoot
Erect Ears
Droopy Ears
Basics of Genetics
Single Gene Effects: Horned vs Polled
•
•
P = Dominant Polled
p or h = Recessive Horned
Basic Genetics
Single Gene Effects: Angus Coat Color
• B = Dominant Black Angus
• b or r = Recessive Red Angus
Basic Genetics
Single Gene Effects: Poultry Skin Color
• W = Dominant White
• w or y = Recessive Yellow
Basics of Genetics
Single Gene Effects: Dwarfism in Cattle,
“Snorter Calves” or “Snorter Dwarfs”
• N = Dominant Normal
• n or d = Recessive Dwarf
Normal (N)
dwarf (n)
Basics of Genetics
Single Gene Effects: Partial Dominance;
Lack of Complete Dominance or CoDominance
• RR = Red Coat, Shorthorn Cattle
• rr or ww = White Coat, Shorthorn Cattle
• Rr = Roan or Spotted Coat, Shorthorn Cattle
Basics of Genetics
• Biochemical Basis of Heredity:
– A living organism is a complex chemical
factory.
– Many chemical reactions are going on all the
time in living organisms.
– Scientists, James D. Watson and Francis
Crick discovered DNA in 1953.
Basics of Genetics
• Biochemical Basis of Heredity:
– DNA = Deoxyribonucleic Acid
– DNA is the basic material of heredity.
– A protein-like nucleic acid making up plant
and animal genes and chromosomes that
controls inheritance.
– Each DNA molecule consists of two strands
in the shape of a “Double Helix.”
Basics of Genetics
Basic Genetics
• Biochemical Basis of Heredity:
– Most inheritance characteristics can be
predicted but some cannot, because some
genes “jump” (are promiscuous).
– Such genes can result in resistance to
pesticides, drugs, etc.
– DNA can reproduce itself, molecule by
molecule, by joining various chemical building
blocks.
Basics of Genetics
• Biochemical Basis of Heredity:
– DNA is the material of which genes are made.
– The DNA molecule has been described by a
few in the scientific community as the
“backbone of the chromosome”, analogous to
the vertebral column, which is the backbone
of the vertebrate animal body.
Basic Genetics
• Biochemical Basis of Heredity:
– DNA molecule resembles a long, twisted
ladder in which two strands (sides) are joined
together by runs.
– Each strand is called a Polymer (poly =
meaning many) and (mer = meaning parts),
because it is composed of many repeating
units of nucleotides.
Basics of Genetics
• Biochemical Basis of
Heredity:
– Nucleotides are composed
of a nitrogenous base
(either a purine or a
pyrimidine) linked to a
sugar, which is in turn linked
to a phosphoric acid
molecule.
Basics of Genetics
The Make Up of an Individual Animal
Heredity
Sire – Sperm
Dam - Ovum
Zygote
Environment
Ration
Disease
Climate
Housing
Water
Manager
Injury
Conception
Birth
Weaning
Sexual Maturity
Death
Selection
Selection
• Natural Selection:
– Refers to the influence of the environment on
the probability that a particular phenotype
survives and reproduces.
– Not all phenotypes are equally Fit to compete
in a particular environment.
– Fitness is the capability of a phenotype and
the corresponding genotype to survive and
reproduce in a given environment.
Selection
• Artificial Selection:
– Refers to a set of rules designed by humans
to govern the probability that an individual
survives and reproduces.
– Individuals capable of surviving may not be
allowed to survive under an Artificial
Selection program because their appearance
or performance does not meet some
standard.
Selection
• Population Genetics:
– Animal breeders are interested in
characteristics of whole groups or large
Populations.
– Animal breeders are concerned with
individuals and particular matings only
because they make a Population what it is.
Selection
• Population Genetics:
– Basic to Population Genetics is the concept
of “Gene Frequency (q).”
– Gene Frequency is a value characteristic of a
particular gene in a particular Population.
Selection
• Population Genetics:
– Gene Frequency is a fraction of the number
of genes of that kind in the total number of
genes in that Allelic Series within that
Population.
– Gene Frequency will have a numerical
value between 0.0 & 1.0. Usually
expressed as a percentage (0 to 100%).
– Permanent genetic changes in Populations
are produced by changes in Gene
Frequencies.
Selection
Factors Which Change Gene Frequencies:
1. Mixture of Populations
2. Mutations
3. Selection (Artificial Selection)
4. Genetic Drift
Selection
Factors Which Change Gene Frequencies:
1. Mixture of Populations:
Example:
•
Assume a herd of 20 ‘white’ registered Shorthorn cows
(rr).
•
The Gene Frequency of “white gene” (r) in this group of
Shorthorn cows = 1.0 or 100%
•
The Gene Frequency of “red gene” in this group of
Shorthorn cows = 0.0
•
If a “red” bull (RR) was mated to these “white” cows (rr)
and produce 20 calves, all of these calves would be “roan”
(Rr), and the Gene Frequency of the “white” gene (r) in the
calves would be 0.5 or 50% as compared to 1.0 in their
dams.
Gene Frequency
• In a herd of 60 shorthorn cows there are
10 red, 20 roan and 30 white. What is the
gene frequency of the red gene? White
gene?
• Red= 10+10+20/120=33%
• White= 20+30+30/120=67%
Selection
Factors Which Change Gene Frequencies:
2. Mutations:
– A change in a gene which causes a sudden
change in the phenotypic expression of that
gene.
– Genes and alleles mutate at different rates.
– Basically most, if not all mutations are due to
a change in the code sent to ribosomes by
the gene by means of RNAm to form a
particular protein.
Selection
Factors Which Change Gene Frequencies:
2. Mutations: (continued)
–
–
–
–
If the wrong code is sent, different proteins are
formed.
The missing protein or the new protein may cause a
defect or a new genetic trait to appear.
Differences we can see or measure between
individuals are due to an accumulation of different
mutations (old or new) within populations.
These mutations are responsible for differences in
coat color, size, shape, behavior, and other traits in
various animal species.
Selection
Factors Which Change Gene Frequencies:
3. Selection (Artificial Selection):
– Can be a potent force in changing the
frequency of a gene or genes in a population.
– Main genetic effect of artificial selection, if
selection is effective, is to change Gene
Frequencies.
– Artificial Selection is the most valuable
tool for an animal breeder.
Selection
Factors Which Change Gene Frequencies:
4. Genetic Drift:
•
•
Frequency of a gene may be quite different than in a
larger population from which the smaller population
was derived.
Example:
If, in a large population, the frequency of gene (A) is
0.5, and if a small group of individuals leave this larger
population (migrate) and settle in another area where
they become isolated, they interbreed.
Selection
Factors Which Change Gene Frequencies:
4. Genetic Drift: (Example continued)
•
The frequency of the Alleles (A) and (a) in this small
group could be between 0.7 and 0.3, or any frequency
depending upon the change.
•
Thus, the frequency of genes (A) and (a) in the new
isolated population could be quite different than in the
original population from which they came.
•
Another way the Gene Frequency could be altered in
the other direction for this small isolated group would be
if a male from another population becomes introduced to
the group, thus a form of “Genetic Drift.”
Selection
Selection
Selection Response:
• Five (5) factors that determine a herd and/or
an animal’s response to Artificial Selection:
1. Heritability
2. Accuracy
3. Selection Differential
4. Generation Interval
5. Number of Traits Selected
Selection
Heritability:
• Heritability is the portion of Total Phenotypic
Variation that is due to Hereditary differences
between individuals.
• Heritability is also a technical term used by
animal breeders to describe what fraction
(portion) of differences in a Trait are due to
differences in Genetic Variation rather than
Environmental Variation.
Selection
Heritability: (continued)
• Heredity Variation is due to additive gene
action.
• Phenotypic expression of genes is that which
can be measured by our senses.
• Phenotype is what can be seen visually as a
Trait or outward appearance of the animal in
question.
• Heritability Estimate = h2.
Selection
Heritability: (continued)
• Heritability Estimate = h2.
• h2 = Genetic Variation
• h2 = Additive Genetic Variation ÷ Total
Variation*
*(Total Variation = Genetic Variation + Environmental Variation)
Selection
Heritability: (continued)
• Genetic Improvement of farm animals depends
upon the existence of Genetic Variation!
• To improve a productive characteristic of an
animal, requires animals within the population
(i.e. herd, flock, breed, etc.) must differ in the
genes they possess that govern the ability to
manifest a specific productive trait.
Selection
Heritability: (continued)
Two (2) kinds of Genetic Variation:
1. Additive
2. Non-additive
Selection
Heritability: (continued)
• Additive Genetic Variation:
– Refers to differences from animal to animal in
those genes in which the changes in genetic
ability due to replacement of one gene with
another which are additive;
– That is, there is a linear change in breeding
value with the addition of successive allelic
substitutions.
Selection
Heritability: (continued)
• Non-additive Genetic Variation:
1. Dominance Type
2. Epistatic Type
Selection
Heritability: (continued)
• Dominance Variation arises when the change
in genetic ability is nonlinear after the
substitution of one allele for another at the same
genetic locus.
• Epistatic Variation arises when nonlinear
changes in genetic ability occur at a locus due to
a gene substitution at a different locus.
Selection
Heritability: (continued)
• Heritability Estimates (h2):
– Heritability Estimates reflect the degree to
which additive gene effects exist in controlling
variation in performance.
– Heritability Estimates fall between 0.0 and
1.0; apart from errors of estimation.
– A Heritability Estimate value near 1.0
suggests that environmental variation plays
little part in variation in performance from
animal to animal.
Selection
Heritability: (continued)
• Patterns are expected in heritability estimates for
various aspects of animal performance.
• Traits associated with reproduction are
expected to have very low heritabilities.
• Traits associated with rate of gain, growth,
carcass traits, body dimensions, and wool
traits will have higher heritabilities.
Selection
Heritability: (continued)
• Heritability Estimates reflect the degree to
which additive gene effects exist in controlling
variation in performance.
• When substantial Additive Variation exists,
selection on phenotypic differences among
animals will change the genetic ability of the
animal population (herd, flock, etc.).
• When Non-additive Variation is substantial,
breeding methods such as crossbreeding or
crossing of different genetic lines will be effective
in improving performance.
Selection
General Trait Values for Heritabilty Estimates
(h2) of Livestock:
Trait(s)
(h2)
Level of Heritability
Range
Reproductive 0.00-0.15
Low
Growth & Milk 0.15-0.25
Medium
Carcass
0.25-0.45
High
Wool/Fleece
0.45-0.65
Very High
Selection
Types of Traits:
1. Qualitative Traits
2. Quantitative Traits
Selection
Qualitative Traits:
• Traits associated with ‘quality’ of the animal;
• Non-measurable;
• Great value to purebred breeders;
• Little value to commercial breeders;
• Examples, i.e. coat color, horns vs polled,
ear carriage, conformation, etc.
Selection
Quantitative Traits:
• Traits associated with ‘quantity’ of product(s)
produced by the animal;
• Measurable via scales, ruler, number count, etc.
• Great value to commercial breeders;
• Less value to many purebred breeders;
• Examples, i.e. weaning weight, average daily
gain, fleece weight, number of piglets
weaned, eggs laid, feed efficiency, milk
production, yield grade, etc.
Selection
Statistics:
• Statistics is the quantitative study of
Populations.
• Population Statistics includes all of the
individuals of that Population (that is identified).
• Sample is a smaller part of the larger defined
Population.
• The “Bell Curve”, the basic statistical
“Binomial Distribution” or “Normal
Distribution” is shown on the next page.
Selection
Statistics:
Selection
Arithmetic Mean, aka Average:
– Mean provides no information about
variability.
Selection
Variance:
– Variance is the best measure of dispersion.
– Standard Deviation is a measure of
dispersion off of the Mean.
– Properties of Standard Deviation:
•
•
•
•
Easy to calculate
Use of all values
Uses Mean as a base
Same units as original
observation.
Selection
Genetic Correlations:
– Genetic Correlations may be determined
statistically, or they may be determined by selection
for only one trait.
– If one is successful in improving one (1) trait, changes
may also happen in another unobserved and
unselected trait.
– A Genetic Correlation means that two (2) or more
traits are affected by the same Genes.
– Genetic Correlations between two (2) traits may
influence the amount of progress (+) or retrogression
(-) made in selection for one of them.
Selection
Genetic Correlations:
• Positive Genetic Correlation (example):
Positive +
Weaning
Weight
Milk
Production
Selection
Genetic Correlations:
• Negative Genetic Correlation (example):
Negative Grade of
Wool
Clean Wool
Yield
Selection
Selection Differential (SD):
• The Selection Differential is the
difference between the Mean of the
“selected parent(s)”, and the average of
the population for their Generation.
Selection
• Selection Differential (SD):
• or
• The average superiority of those selected for
parents over the average of the population
from which they were selected.
SD = ½ X ( SD + SD)
Selection
Selection Differential (SD):
• The magnitude (size) of the Selection
Differential is dependent upon the
number of individuals that can be Culled.
(Culling is the opposite of Keeping)
Selection
Selection Differential (SD):
• The more traits selected for, the smaller
the Selection Differential.
• This ‘fact’ is because it is more difficult to
find an individual that excels in two (2) or
more traits; than it is to find an individual
that is excellent for only one (1) trait.
Selection
Generation Interval (GI):
• The Generation Interval (GI) is the
average age of the parents when the
offspring are born.
• Early breeding of both males and females
in a herd or flock can reduce Generation
Interval.
Selection
Generation Interval (GI):
• Typical Generation Intervals for some
species:
– Swine
– Cattle
– Sheep
– Horses
– Humans
2 to 3 years
4 to 6 years
3 to 4 years
9 to 13 years
30 to 35 years
Selection
Artificial Selection
• Response:
Annual
Genetic =
Progress
SD
h2
GI
SD x h2
GI
Average
+ for
Trait Selected
= Selection Differential
= Heritability Estimate value for a specific trait
= Generation Interval
Selection
Genetic Progress for one (1) Year:
Annual
Genetic =
Progress
SD x h2
GI
Average
+ for
Trait Selected
Example:
• A herd of cattle had an average weaning weight, with calves
adjusted to a standard.
• The average adjusted 205 day weight for the herd was 400 lbs.
• The bull calves selected for breeding weighed an average of 500
lbs.
• The heifer calves selected for breeding weighed an average of 450
lbs.
Selection
Genetic Progress for one (1) Year:
• Thus:
– SD for bull calves = 500 – 400 = 100 lbs.
– SD for heifer calves = 450 – 400 = 50 lbs.
– SD for both selected parents = 100 + 50 ÷ 2 = 75
lbs.
– If h2 for adjusted 205 day weaning weight of beef
cattle is 0.25 (25%)
– Then the expected improvement in weaning
weight is 0.25 x 75 lbs=18.75 lbs.
Selection
Genetic Progress for one (1) Year:
• Thus: (continued)
– If the average age of the cows at the time of calving
was 4 years, and the average age of the bulls used to
produce these calves at the calving of these calves
was 3 years, then calculate the Annual Genetic
Progress expected from these potential selected
breeding parents.
– GI = 4 + 3 = 7 ÷ 2 = 3.5 Years Generation Interval
– The expected AGP; 18.75 ÷ 3.5 = 5.36 lbs.
increase/year in adjusted 205 day weaning
weights.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding
2. Linebreeding
3. Outbreeding
4. Crossbreeding
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding:
•
•
•
The production of progeny by parents that are more
closely related than the average of the population
from which they came.
Common ancestors within the last 3 or 4
generations.
Major genetic effect of INBREEDING is to increase
the number of pairs of genes that are
HOMOZYGOUS in an INBRED POPULATION.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding:
• INBREEDING does not create RECESSIVE
GENES, it makes them noticed more.
• Increased HOMOZYGOSITY due to
INBREEDING increases “BREED PURITY”.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding:
• Increased HOMOZYGOSITY due to
INBREEDING also tends to fix RECESSIVE
GENES in a small INBRED POPULATION.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding:
• Increased HOMOZYGOSITY due to
INBREEDING when combined with
SELECTION, can be used to eliminate
detrimental RECESSIVE GENES from an
INBRED POPULATION.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
1. Inbreeding:
• The main reason for INBREEDING is to
produce INBRED LINES that may be used in
crossing purposes to take advantage of
“HYBRID VIGOR”.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
2. Linebreeding:
• This is a form of INBREEDING in which an
attempt is made to concentrate the
inheritance of one (1) or more outstanding
ANCESTORS IN A PEDIGREE.
• HOMOZYGOSITY does not usually increase
as rapidly as it does in INBREEDING.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
3 Outbreeding:
• This is the mating of UNRELATED
FAMILIES WITHIN THE SAME BREED.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
4. Crossbreeding:
• This is the mating of individuals from
DIFFERENT BREEDS.
• A CROSSBRED is more intense in its
GENOTYPIC and PHENOTYPIC effects
than in OUTBREEDNIG, but the effects are
similar.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
4. Crossbreeding:
•
•
Main genetic effect of CROSSBREEDING is the
INCREASED HETEROZYGOSITY or DECREASED
HOMOZYGOSITY within the population that it is
practiced.
Main PHEONOTYPIC effects of
CROSSBREEDING is an increase in PHYSICAL
FITNESS or traits related to PHYSICAL FITNESS.
Applied Animal Breeding
Mating Systems for Livestock Improvement:
4. Crossbreeding:
•
•
•
Crossbreeding = Hybrid Vigor = Heterosis
HYBRID VIGOR is the superiority of the
CROSSBRED offspring over the average of the
PUREBREDS used to make the cross.
HYBRID VIGOR includes more than just
HARDINESS……it tends to produce greater
VARIABILITY, and may include faster growth rate,
more production, and better fertility.
Systems of Selection
1. Tandem Selection
2. Independent Culling Level
3. Selection Index
Systems of Selection
1. Tandem Selection:
•
•
•
One trait is selected for at a time until
maximum progress has been achieved for
the trait being selected.
Then another trait becomes the focal target
for improvement.
This system of selection is slow.
Systems of Selection
2. Independent Culling Level:
•
•
Minimum standards are identified or set for
several traits within the herd or flock.
The failure by any animal to meet any one
trait, results in it leaving the breeding herd.
Systems of Selection
3. Selection Index:
•
•
•
A SELECTION INDEX is a mathematical
scoring system, giving weighted values for
any number of ECONOMICALLY
IMPORTANT TRAITS.
Animals then are ranked based on an
INDEX COMPUTED.
The SELECTION INDEX system is widely
accepted in the United States.
Systems of Selection
3. Selection Index:
•
•
Below average animals are CULLED.
The SELECTION INDEX system can be
tailored to fit a scoring and weighted system
to one’s farm and/or ranch needs.
Systems of Selection
3. Selection Index:
•
•
Computers and even programmable
calculators can be utilized.
Some livestock breed associations have
CUSTOMIZED SELECTION INDEX
selection systems for use by their
breeders.
Total Performance Index
(Dairy Cattle)
Wean Wt. Index (Beef)
Speed Index(AQHA)
• Speed Index points
OFFICIAL DISTANCE
MINIMUM STANDARD TIME (for 100
Speed Index Rating)
220 yards - straightaway
11.95
250 yards - straightaway
13.35
300 yards - straightaway
15.55
330 yards - straightaway
16.95
350 yards - straightaway
17.85
400 yards - straightaway
20.15
440 yards - straightaway
22.05
550 yards - straightaway
27.70
660 yards - straightaway
33.50
660 yards - around one turn
34.60
770 yards - around one turn
40.36
870 yards - around one turn
45.60
•
•
•
•
•
•
•
•
•
•
•
.087 equals one speed index point at 870 yards.
.077 equals one speed index point at 770 yards.
.066 equals one speed index point at 660 yards.
.055 equals one speed index point at 550 yards.
.044 equals one speed index point at 440 yards.
.04 equals one speed index point at 400 yards.
.035 equals one speed index point at 350 yards.
.033 equals one speed index point at 330 yards.
.03 equals one speed index point at 300 yards.
.025 equals one speed index point at 250 yards.
.022 equals one speed index point at 220 yards.
Speed Indexes
• To calculate a specific speed index for a specific horse in a specific race,
the time run by the horse is compared to the speed index time associated
with “100” for the distance in question at that particular track. Points are
added or subtracted based on whether the time was faster or slower than
“100” speed index time. The only exception to the point interval chart
above relates to a horse achieving a speed index of “101”. In order to
achieve a speed index of 101, a horse need only be .01 faster than the speed
index time associated with 100. Thereafter, speed indexes greater than 101
are calculated using the speed index point intervals above. By way of
example, if a 100 speed index associated with a 350 yard race is 17.75, then
a horse that runs a 17.74 shall earn a speed index of 101. Using the same
example, if the horse runs a 17.705 (.035 faster than 17.74), then such
horse shall earn a speed index of 102.
QUESTIONS?
More Math Anyone?