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Evolution of Livestock Breeds
How do breeds adapt and change?
What is their history?
Why does it matter?
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I. What is a breed?
A. Animals that, through selection and breeding, have come to
resemble one another and pass those traits uniformly to their
offspring.
1. Unfortunately this definition leaves some unanswered
questions. For example, when is a crossbred animal
considered a composite breed and when do we stop thinking
about them as composites? The Genetics of Populations by
Jay L. Lush helps explain why a good definition of "breed" is
elusive.
a.
2.
A breed is a group of domestic animals, termed such by common
consent of the breeders, ... a term which arose among breeders of
livestock, created one might say, for their own use, and no one is
warranted in assigning to this word a scientific definition and in
calling the breeders wrong when they deviate from the formulated
definition. It is their word and the breeders common usage is what
we must accept as the correct definition.
Dr. Lush's definition helps us understand that it is at least in
part the perception of the breeders and the livestock industry
which decides when a group of individuals constitutes a
"breed".
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I. What is a breed?
B. Breeds are primarily
distinguished by visual
characteristics: color,
pattern, polled or horned
condition, or extreme
differences in form and
shape.
1. Composite or synthetic
breeds: new breeds being
developed that combine the
desirable characteristics of
several existing breeds.
2. Purebred: purity of ancestry;
only animals in that particular
breed have been mated to
produce the animal in
question.
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II. Breed Development
A. The development or evolution of breeds can
take different routes.
1. Sometimes, change that can occur as the result
of selection for a small number of traits
a. Holstein cattle have been selected primarily for milk
production and are the highest milk producing cattle in
the world.
b. The Bedouins of the desert developed Arabian horses
with strength, courage and stamina required for
survival, and for the speed and responsiveness needed
to win the tribal skirmishes.
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II. Breed Development
2. Other breeds have traits that result from natural selection
pressure based upon the environment in which they were
developed.
a. N’dama cattle from West Africa have, through the centuries,
developed a resistance to trypanosomiasis or sleeping sickness
spread by the tse-tse fly, which is fatal to most other breeds of
cattle.
b. The Chincoteague Pony descended from the feral horses on a
barrier island off the coast of Maryland and Virginia. 80% of their
diet is coarse saltmarsh cordgrass and American beachgrass; their
diet also includes poison ivy. The high concentration of salt in their
diets causes the horses to drink twice as much fresh water as
domestic horses and have a "bloated" appearance.
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II. Breed Development
B. Adaptations of an animal determine its niche in
the environment.
1. Adaptation: evolution of structural, internal, or
behavioral features that help an organism better
survive in an environment.
a. The large eyes of nocturnal animals.
2. Niche: the role of a particular species in a
community regarding food, space, reproduction, etc.
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II. Breed Development
3. Structure and Behavior Determine Environment
a. Structure
1. Sharks have characteristics that enable them to survive in
water, a streamlined body design and teeth that re-grow to
replace broken ones.
2. The artic fox’s coat changes color for camouflage.
b. Behavior
1. Bears survive a long, cold winter by hibernating.
2. Pigs are difficult to herd and move long distances, so they are
used mostly in farming communities.
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II. Breed Development
C. Livestock have evolved over time through
genetic changes that are both natural and
selected by man.
1. Mutation: random error or change in the DNA
sequence that may effect whole chromosome or one
gene.
a. This usually results in a negative result.
2. Natural Selection: a mechanism that explains how
populations evolve; organisms with favorable
variations survive.
a. The Romney breed of sheep respond to it’s geographic and
climatic conditions with hooves that are resistant to foot rot
and fleeces that remain healthy in harsh weather.
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II. Breed Development
3. Reproductive Isolation: occurs when organisms
that formerly interbred are prevented from
producing offspring.
a. By developing different mating times.
b. By geographic factors
c. This is often induced by man.
D. All these factors can lead to a new breed or
even a new species
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III. Why is biodiversity important?
A. Why are we concerned about preserving
information about minor, or relatively unknown,
breeds of livestock?
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III. Why is biodiversity important?
1. Holstein cow example
a. Holstein has advantage over other breeds in the
production of whole milk, this advantage is based on
feeding high levels of cereal grains and pricing that
favors low milk-solids content.
b. The Dutch Belted breed displayed excellent milking
ability in a grass-based dairy situation in trials in the
early 1900s and would be more preferable if cereal
grains weren’t available.
c. In Australia, composite breeds, such as the Australian
Friesian Sahiwal, have been developed which have
higher milk production levels than Holsteins in the
tropical regions of that country.
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III. Why is biodiversity important?
2. Natural resistance to diseases or parasites
example
a. Some breeds of sheep have a natural resistance
to internal parasites. Should vaccines become
restricted or uneconomical, then a breed such as
the critically endangered Gulf Coast Native, with
the parasite resistance it has developed through
natural selection, could be of critical importance
in the sheep industry.
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III. Why is biodiversity important?
B. Genetic diversity
should be maintained
to help meet the
potential challenge
resulting from
changes in production
resources and market
requirements.
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Now, it’s your turn to research!
• As is states on your worksheet, you should visit
this website:
http://www.ansi.okstate.edu/breeds/
• Click on the species assigned to you by your
instructor: cattle, goats, horses, sheep, swine,
or other
• Click on a breed you have never heard of before
and answer the questions on your worksheet as
they relate to that breed.
– If you pick a breed that does not answer most of the
questions, switch to a different breed.
• Be prepared to tell the class about the
information you find.
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