Lecture 4 Flashcards
(25 cards)
What is selection
Choice based on record information, which animal should be saved or rejected for breeding purposes
What are the 3 animal selection methods
- Tandem selection methods
- Independent culling selection method
- The selection index
What is tandem selection
Selection is practised for only one trait at a time until satisfactory improvement is achieved
What are the disadvantages of tandem selection
- Time and effort expended by breeder are not simultaneously rewarded by the amount of genetic progress made, hence it is the least efficient
- Genetic correlation between the traits selected for determine the efficiency and genetic progress made using the selection method
How is efficiency improved in tandem selection
If there is positive correlation between the traits selected, an improvement in one results to an improvement in the other trait not selected for
How is there zero correlation with tandem selection
Of the two traits are inherited independently no genetic association exists between them and efficiency is reduced
What does a negative correlation association lead to with tandem selection
Association south nullify or neutralise the progress made in selecting for any one trait. This demoralises and discourages one given the long period of time that would have been wasted
What is the independent culling selection
The method involved selection for two or more traits at a time, but for each trait, a minimum standard is set that an animal must meet in order to be saved for breeding purposes
What is the major disadvantages of the independent culling selection
It is possible to cull some genetically superior individual that is excellent in one trait but falls below the average in another trait
What is the selection index method
Required the separate determination of the value or economic weight for each of the traits selected for, and the addition of these economic weights to give a total score for all traits
What animals are kept with the selection index method
Animals with the highest total scores are kept for breeding purposes
What is SI correlations and heritability
More genetic progress and improvement are achievable by this method as a result of increased efficiency for the time and effort expended by the animal breeder if the index is properly constructed
What are the 5 steps in the selection index method
- Formulate breeding objectives
- Determine population mean
- Determine relative economic weights
- Compute economic weight = RI
- Construct selection Index for determining estimated breeding value (EBV):
SI = (1.500)(BW)+(0.162)(BL)+(0.059)(CG)
What does the animal breeding system depend on (4)
- Type of livestock operation
- Size of the herd
- Available money
- Breeding goals of the farmer
What are the two system of breeding
- Straight breeding
2. Crossbreeding
What is pure breeding
A purebred animal has the characteristics of the breed and both parents of a purebred animal must have been purebred
What is inbreeding
Mating of related animals
What is close breeding
Most intensive form of inbreeding. Animals are very closely related and can be tracked back to more than one common ancestor
What is line breeding
Is the mating of more distantly related animals traced back to one common ancestor
What does inbreeding increase
Genetic purity of the stock and the offspring become homozygous
What is outcrossing
The mating of animals of different families within the same breed
What is line crossing
Mating of animals from two different lines of breeding within a breed
What is grading up
Mating of purebred sired to grade females
What does grading up improve
Quality of animals
