Since domestication man has tried to apply artificial selection to change the animal population for making genetic improvement in performance. The different breeds of domestic animals that exist today are the result of natural and artificial selection. However in India artificial selection in our indigenous breeds does not applied so far and more genetic improvement is needed for production of milk and meat from goats.
The selection is a process of giving preference to certain individuals in a population to reproduce than other individuals which are denied the opportunity to produce next generation. Therefore, selection is a choice of individual to produce next generation.
Selection is keeping some animals and culling others in an effort to improve traits in proportion to their heritability and economic importance. In establishing new flocks or improving older ones, goat breeders striving in improvement in their animals have basis of selection, (1) Individual merit, (2) Selection based on pedigree, (3) Selection based on family member performance and (4) Selection based on Progeny performance.
Since the amount of selection for any particular trait is limited, it is important to emphasize in selection those traits for which the greatest progress can be made and those which are more valuable.
Heritability estimates for goats
|Age at first kidding||55|
|Weight at 7 months||63|
|Mature body weight||50|
|Milk yield per lactation||39|
|Percent fat content of milk||40|
|Rate of gain||30|
This table lists economically important traits of goats and their approximate heritability. That goats shows variations in these characteristics is generally recognized. The problem is to measure these differences from the standpoint of discovering the most desirable genes and then increasing their concentration, and at the same time, culling the animals of less desirable traits.
Kids marketed per Doe
At present 45% of the total goat population replaced every year (40% slaughter + 5% mortality) and annual growth rate is nearly 5%. It seems that goat population is roughly increasing at the rate of 50% per year. Remaining population has 50-50 male and female. Average prolificacy of Indian goats is average at 2 kids per goat. This would be increase by proper selection.
Economically, experiments indicate that Does having twins wean an average of 8-10kg more kid per Doe-year that does of the same age with singles. Thus even though multiple births have low heritability (transmitting ability from one generation to next) any gain no matter how small, is worthwhile. Because multiple births at first kidding are less frequent, young mothers having multiple births are more likely to transmit this trait.
There is need to know the approximate amount or percentage of change in each economically important character which is due to heredity and the amount which is due to environment. Actually, heritability estimates for any one trait vary due to differences in breed, accuracy of measurement, importance of environmental effects which cannot be adjusted, and genetic differences in the particular strains or flock involved. Using Flock Records in Selection
We can make your recording easy and worth to use in improvement of your existing flock. On-the-farm records are the first step towards successful production testing and selection. All too often a breeder remember s the good individuals produced by a given and forgets those which are less producing or culls.
Prerequisite for any production data is that each animal be positively identified – by means of proper identification like ear notches, ear tags or tattoos. Recording of weights and grades does require additional time and labor – an expenditure which is highly worthwhile, however.
Information on the productivity of close relatives can supplement that on the animal itself and thus be a distinct aid in selection. This is especially important when traits such as milk production, kidding rate, and semen production, cannot be measured in both sexes.
Estimating rate of progress For the purpose of illustrating how the heritability may be used in practical breeding operations, let’s see the following example;
In certain flocks of goats, the kids in a given year average 2kg at birth. There are available sufficient of the heavier kids (averaging 2.5kg) from which to select replacement breeding stock. What amount of this heavier birth weight (0.5kg above the average)is likely to be transmitted to the offspring of these heavier kids?
- 2.5kg – 2.0kg = 0.5kg, the birth weight by which the selected lambs exceeds the average from which they arose.
- You can see in above table that birth weight of kid 30% heritable this means that 30% of the 0.5kg can be expected to be due to the superior heredity of the stock saved as breeders and that 70% is due to environment (feed, care management etc)
- 0.5 x 30% = 0.15kg, which means that for birth weight the stock saved for the breeding flock is 0.15kg superior genetically to the stock from which it was selected.
- 2.0 + 0.15kg birth weight, which is the expected performance of the next generation.
The 2.15kg birth weight is merely the expected performance.The actual outcome may be altered by environment and by chance. Factors influencing rate of progress;
- The heritability of the character
- The number of traits for which selection is the same time
- The genotypic and phenotypic correlation between traits
- The amount of heritable variation measured in such specific units as pounds, inches, numbers etc.
- The accuracy of records and adherence to an ideal
- The number of available animals
- The age at which selection is made
- The generation interval
- The caliber of sires