Selection is used as a tool for livestock improvement. A breeding stock is a group of males and females which act as parents of future generations.
Selection is the process of allowing certain animals to be parents of future generations while culling others.
Culling is the removal of animals which do not perform to the desired level, from the herd. The animals retained have certain desirable characteristics which make them produce more.

Selected animals make up the breeding stock.
The breeding stock should pass the good qualities to their offsprings for better performance, to improve the livestock.
Selection process repeated for many generations increases chances of formation of desirable qualities in an animal.
Genetically termed as gene frequency(occurrence of the genes that carry desirable characteristics.) Selection increases occurrence of desirable genes and decreases occurance of undesirable genes.
During selection, the characteristics to be selected for are first studied closely to ascertain that it is not influenced by the environment, but mainly by the genetic make-up.
Selection helps improve characteristics which are highly heritable.
Heritability means the likelihood of a particular trait to be transmitted to the offspring and they are strongly inherited.
A character like milk yield is lowly heritable, i.e. it is weakly inherited and a bigger percentage of the character is affected by the environment.

The degree to which selection affects a character depends on the following factors;
The heritability of the character, The intensity with which the selection is done and the interval between generations and kind of selection being practiced.

Factors To Consider When Selecting A Breeding Stock.

• Age
• Level of performance
• Physical Fitness

• Health
• Body Conformation
• Temperament or Behaviour
• Quality of products
• Mothering Ability
• Adaptability
• Prolificacy

Age

• Young animals,
• Those that have not parturated for more than 3-times, should be selected.
• They have a longer productive life.
• Old animals are poor breeders and low producers.
• Production and breeding efficiency decline with age.

Level of performance

• Animals with highest production level selected.
• Performance best indicated by records.

Good performance of animal indicated by;

• High milk, wool and egg production,
• Good mothering ability
• High prepotency which is the ability of a parent to pass good qualities to their offsprings.
• The animals with poor performance should be culled.
• Good records kept and used by the farmer for this purpose.

Physical Fitness
Animals selected should be free from any physical defect e.g.

• mono-eyed,
• limping,
• irregular number of teats,
• scrotal hernia,
• defective and weak backline

Health

• Sick animals do not breed well and are expensive to keep.
• Animals that are resistant to diseases pass these characteristics to their offsprings

Body Conformation

• Animals for breeding to be selected according to proper body conformation.
• A dairy cow should be wedge-shaped with a large udder, thin legs, long neck.

Temperament or Behaviour

• Animals with bad behaviors should be culled. e.g Cannibalism, egg eating, aggressiveness, kicking

Quality of products

• Select animals that give products of high quality such as meat, wool, eggs, milk.

Mothering Ability

• Animals selected should have a good mothering ability,
• That is animals with good natural instinct towards their young ones.
• This will enable them to rear the young ones up to weaning.

Adaptability
Animals selected should be well adapted to the prevailing climatic condition in the area e.g Ardi and semi arid areas.

Prolificacy

• Animals selected should be highly prolific.
• That is, animals with the ability to give birth to many offsprings at a time(larger litter).
• This is a quality that should be considered when selecting pigs and rabbits.
• The ancestry records assist to choose the prolific breedsfor mating

SELECTION OF CATTLE AND SHEEP
Selection in cattle

Consider the following;

Level Of Performance Which Include;

• Milk Yield Buter Content.

• Length Of Lactation Period.

• Calving Intervals.

Age of the Animal, Fertility, physical Fitness, Health Of The Animal, Body Conformation and suitability of the enterprise-milk or beef

Selection in sheep

Consider the following;

Level of performance which includes;

• Mothering ability

• Growth rate

• Wool quality

• Carcass quality

• Twining rate Age

Suitability to the enterprise-wool or mutton
Flocking instinct Health of the animal
Physical fitness
Inheritable defects
Fertility
Inheritable defects.
Fertility.

Selection in Goats
Consider the following:
Fertility.
Mothering ability.
Growth rate.
Twining rate
Carcass quality/dressing percentage
Growth rate.
Suitability to the enterprise - milk or mutton.
Health of the animal.
Age.

Selection in Pigs

Consider the following:
Carcass quality/dressing percentage
Suitability to the enterprise (bacon or pork)
Growth rate.
Health of the animal.
Mothering ability.
Prolificacy.
Number of teats
Temperament.
Body formation.
Age.
Heredity defects

Selection in Camels
Health of the animal.
Age.
Temperament.
Foraging ability.
Fertility.
Level of performance-milk, meat, fur and transport.

METHODS OF SELECTION

These include:

Mass selection - Animals with superior characteristics (highly heritable breeds) are selected from a herd and then allowed to mate among each other at random. The offsprings will show higher performance than their parents. This is because mass selection increases the occurrence of the desirable genes in a population.

Progeny testing - is a offspring resulting from selected parents ( Family selection).In this method a group of progenies (offrprings) are used as an aid to increase accuracy in the selection ofa breeding stock. This is method is used when the character to be selected is of low heritability and expressedby one sex only.
This methodtakes upto nine years for the results to be seen

Contemporary comparison
Contemporaries refers to other heifers in the herd sired by the same bull.
This is a progey tasting method which involves comparison of average production of daughters (Heifers) of each bull with that of the other heifer refered to as contemporaries.
In this methods it is assumed that thedifference between the herds of the same breed are non-genetic in origin.

advantages

• It is possible to compare heifers of different ages in different locations worldwide.
• It eliminates difference brought about by the environment.
• it is possible to make direct comparison of stut bulls at different artificial insemiation centres.
• It is accurate since we are using a large herd of animals.