Lecture 4 - Animal Selection Methods and Breeding System

Question 1

What are the three selection methods?

Answer 1

• Tandem selection
• independent culling
• selection index

Question 2

What is tandem selection and what are the advantages and disadvantages?

Answer 2

a selection method to select for one trait until the trait is at a satisfactory achievement.
if the genetic correlation is positive the one trait may also improve another.
Disadvantages are it takes time and effort and it the least efficient method.

Question 3

What does zero correlation mean?

Answer 3

When two traits are inherited independently with no genetic correlation.

Question 4

What is independent culling selection?

Answer 4

Method of selecting two or more traits but they both need to meet a minimum standard. It is very strict if the animal didn’t meet one trait it would be rejected.

Question 5

What are some disadvantages of tandem?

Answer 5

• possible to cull some genetic superior individuals due to them falling a little below the cut off.
  This is used to select for body conformation in show cattle and breed coat colour.

Question 6

Is independent culling better or worse than tandem?

Answer 6

Independent culling is better than tandem since selection it selects for more than one trait at a time.

Question 7

What is selection index?

Answer 7

A method which requires separate determination of the value or economic weight with a total score of ALL traits. the animals with the highest scores are kept for breeding.

Question 8

Which of the three methods is most efficient?

Answer 8

The selection index is more efficient because even if the animal is deficient in one trait but exceeds in others it would still be selected in breeding.
There is also more genetic progress is improvement.

Question 9

What are the steps of selection index method?

Answer 9

• formulate breeding objectives (weight, length girth etc)
• determine population mean
• determine relative economic weights
• compute economic weight
• construct selection index for determining estimated breeding value.

Question 10

What do breeding systems depend on?

Answer 10

• operation
• herd size
• money
• goals

Question 11

What are the two breeding systems?

Answer 11

• straight breeding (same breeds)

- cross breeding (different breeds)

Question 12

What does straight breeding include?

Answer 12

• pure breeding
• in breeding
• out crossing
• grading up

Question 13

What does cross breeding include?

Answer 13

two breed, three breed and rotational crossing

Question 14

What is a pure bred?

Answer 14

An animal has the characteristics of the breed and both parents of purebred animals.

Question 15

What is inbreeding?

Answer 15

The mating of related animals.

line breeding and close breeding refer how closely the animals are related

Question 16

What is close breeding and how is it different to inbreeding?

Answer 16

• animals are very closely related and is traced back to more than one ancestor (sire and dam, brother and sister).
• line breeding is mating of more distantly related animals where there is one common ancestor (cousins and half brother and sisters).

Question 17

Inbreeding purpose?

Answer 17

• increases genetic purity of the stock and offspring becomes homozygous.

Question 18

What is outcrossing?

Answer 18

mating of animals of different families within the same breed they are NOT closely related.
This brings traits that are more desirable but not present in original animals.

Question 19

What is line crossing?

Answer 19

This is the mating of animals from two different lines but within the SAME breed.

Question 20

What is grading up?

Answer 20

mating of purebred sires to grade females.
this improves the quality of animals.
This selects the highest quality sire with an improvment from first cross = 50% and second generation 75% etc.

Question 21

What is cross breeding?

Answer 21

mating of two unrelated animals of DIFFERENT breeds to make a hybrid.
the offspring traits are improved.

Question 22

What are cross breeding considerations?

Answer 22

• good record keeping
• birthing difficulties
• maintenance costs
• AI
• different pastures to avoid unwanted breeding