Artificial insemination
Artificial insemination: very simply means taking sperm from the best male
animal and putting into the best female animal. It is used extensively in
modern farming to produce diary and beef cattle and also in the breeding of
race horses.
Semen is collected from a prize bull. It is then diluted, frozen and stored. It
can then be either inserted directly into a fertile cow or super-ovulation +
embryo transfer can be used. This technique involves a prize cow being
given hormones to increase ovulation. Eggs are then collected and fertilised
in vitro by sperm from the prize bull. An embryo is then implanted into a
surrogate cow, which gives birth to the calf.
Advantages of artificial insemination
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Use of proven stock quality
Frozen semen can be transported globally and stored for many years
Cost effective a straw of semen is £15 while the cost of a Holstein bull
is around £10,000. A bull is expensive to rear, relatively unproductive,
vulnerable to disease or accident and may be infertile.
Flexibility: high yield dairy cows can be crossed with dairy bull semen to
create higher yield cows.
Safety: bulls are aggressive
Main disadvantage of artificial insemination
Is that the same alleles keep appearing in the population so there is a loss of
diversity in the gene pool (many genes are lost). So a disease could wipe out
an entire population if resistant alleles have been lost.
TASKS:
1.
Produce a set of annotated diagrams explaining how semen is
collected, stored and finally inserted into a cow during artificial
insemination.
2.
List the advantages of artificial selection over natural breeding.
Use the information provided above as a starting point and then
supplement from your own research. Use MSN Messenger to discuss
your list with a partner in the class. Bring your list to the next lesson for
display.
3.
Complete the dating game below and then answer the questions.
Dating game
Use the following website: sire selector to mate an imaginary herd of ten milk
cows with the semen from a bull or bulls of your choice.
Produce a family tree of the crosses and provide information on projected
milk yield for the likely calves produced. You have only a limited budget of
£150 to spend and must produce the new herd with the highest projected milk
yield possible.
Remember: a cow will usually only produce 1 calf at a time and it can be
either male or female (1:1 ratio).
Lay out your family tree with projected milk yields on an Excel spreadsheet
for display next lesson.
Copy and answer these questions:
1.
What would you do as a farmer if a calf when fully grown into a cow
failed to give the projected milk yield?
2.
What would happen to the male calves produced during the crossings
(remember 1:1ratio of males to females would occur)?
3.
What advantages does artificial insemination have over a natural
breeding programme for the farmer?
4.
How could in-vitro fertilisation using super-ovulation + embryo transfer
further improve the selection of your milk herd?
5.
Do you think it is right that we tamper with natural selection by these
artificial means?