METHODS OF
SELECTION
INTRODUCTION
INTRODUCTION
• Pedigree method
• In this method, selection is done on the basis of the
individual's record of inheritance.
• A pedigree to be of value should include the performance
record of the immediate parents of the individual being
considered for selection.
• Unless the immediate ancestors including the grandparents of
the individual are outstanding producers and superior
individuals, pedigree selection is meaningless and it can even
ruin the whole herd.
INTRODUCTION
• Pedigree method
• The boar should always be purebred, which means that he is
of known ancestry.
• This alone is not enough, for he should also be a good
representative of the breed selected; and his pedigree should
contain an impressive list of noted animals.
• Likewise, it is important that the sows be of good ancestry,
regardless of whether they are purebreds, grades or
crossbreds.
• Such ancestry and breeding give more assurance of the
production of high quality pigs that are uniform and true to
type.
INTRODUCTION
• Independent culling level method
• This method establishes minimum standards for each character, and
selecting simultaneously but independently for each character.
• The performance in one trait is considered entirely independent
of the performance in other traits, or the performance in one
trait does not affect the performance in another.
• The culling level to be established for each trait is determined
on the basis of the heritability of that trait, its economic
importance and the percentage of the animals which are to be
culled.
INTRODUCTION
• Independent culling level method
• This system, in which several of the most important characters are
selected for simultaneously, is without doubt the most common
system of selection.
• It involves establishing minimum standards for each character and
culling animals which fall below these standards.
INTRODUCTION
• Independent culling level method
• For example, it might be decided to cull all pigs in litters of less than
seven pigs, or weighing less than 18 kg. at weaning, or gaining less than
0.9 kg. per day from weaning to 100 kg. Of course, the minimum
standards may have to vary from year to year if environmental
factors change markedly (for example, if pigs average light at weaning
time due to a disease).
INTRODUCTION
• Independent culling level method
• The chief weakness of this system is that an individual may
be culled because of being faulty in one character only, even
though he is well nigh ideal otherwise.
• This system is most effective when you are considering only
a few traits at a time and when you find it necessary to cull
many animals and keep a few impressive ones.
• Its effectiveness goes down as the number of traits
included in the selection program increases and when the
culling pressure decreases.
INTRODUCTION
• Tandem method
• This refers to that system in which there is selection for only one
trait at a time until the desired improvement in that particular trait
is reached, following which selection is made for another trait, etc.
• This system makes it possible to make rapid improvement in the trait
for which selection is being practiced, but it has two major
disadvantages:
• Usually it is not possible to select for one trait only,
• Generally income is dependent on several traits.
• Tandem selection is recommended only in those rare herds
where one character only is primarily in need of improvement;
for example, where a certain herd of pigs needs improving in
litter size.
INTRODUCTION
• Selection index method
• This method combines all important traits into one overall
value or index.
• Theoretically, a selection index provides a more desirable
way in which to select for several traits than either tandem
method or independent culling method.
INTRODUCTION
• Selection index method
• Selection indices are designed to accomplish the following:
• To give emphasis to the different traits in keeping with their
relative importance;
• To balance the strong points against the weak points of each
animal;
• To obtain an over-all total score for each animal, following which
animals can be ranked from best to poorest;
• To assure a constant and objective degree of emphasis on each
trait being considered, without shifting of ideals from year to
year; and
• To provide a convenient way in which to correct for environmental
effects, such as feeding differences, etc.
INTRODUCTION
• Selection index method
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INTRODUCTION
• Selection index method
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