Heritability Definition, and How To Calculate Its Value – The livestock businesses make various efforts in improving livestock productivity. However, often productivity increases are only done by modification of feed and environmental control efforts, and forgetting test factors. Whereas genetic factors are one of the factors that determine the productivity of livestock.
For example, previous studies have suggested that more than 40% of dairy milk production are genetically influenced. The question is, how do we increase the productivity of livestock by considering genetic factors, one of the ways by making a selection. Choosing livestock by having the productivity of the population, then breeding it. Well, there is one thing that can be said the most important thing in carrying out the selection is heritability.
There are two definitions of heritability, namely in the broad sense and in the narrow sense, but what is used in general is in a narrow sense. because it is able to show the rate of change that can be achieved by selection for a trait within the population
Heritability in a broad sense is the total or a summation between genetic, dominant and epistatic varieties divided by total or the summation between genetic, dominant, epistatic and environmental varieties.
While heritability in a narrow sense, namely: Genetic variety per total or summation between genetic variety, dominant, epistatic and environment.
The heritability value of a trait ranging from 0 to 1. Properties that have high heritability values (in a narrow sense) tend to be more controlled by additive genes compared to Non additive. Therefore heterosis tends to be less influenced by additive genes, the higher the heritability value of a trait will be the smaller the heterosis. In contrast, traits that have low heritability such as litter size in pigs, calving rate in cows and sheep generally show a fairly high heterosis.
The value of h2 is intermittently between 0-1. Heritability is categorized as lowly heritable and high highly heritable when it has 0-0.15: 0.015-0.30 and >0.30 respectively. A value of h2 approaching 1 indicates that a trait provides a better response to the reverse selection treatment, a low h2 value indicates that the selection response will be slow.
How to Calculate Heritability Value
Heritability value can be calculated by comparing or measuring the relationship or similarity between the production of individuals that have kinship relationships.
Heritability value can be calculated using several estimation methods, including through the equation of phenotypes of livestock that have a family relationship, namely between siblings (full sib), half sib, between parents and children (parent and offspring). In addition, it can also determine the real heritability (realized heritability) based on the progress of the selection.
The estimated value of heritability can also be obtained by calculating the value of ripitability, i.e. The appearance of the same trait at different times of the same individual throughout its life. Ripitability can be used to suspect individual traits in the future.
The estimated heritability of some important economic properties in sheep was expressed by Lasley (1978) which included: the heritability value of the number of children born was 0.10 – 1.15; birth weight 0.30 – 0.35; weaning weight 0.30 – 0.35; one year’s life weight 0.40 – 0.45; weight gain after weaning 0.40 – 0.45; body type 0.20 – 0.25 and condition score 0.10 – 0.15.
Another way of estimating the value of heritability is to use identical twin animals from one egg. Identical twins have the same genotype so the difference in producing properties among twins is caused by non-genetic factors.
Important economic properties in hens include: hen mortality, laying hen mortality, egg production, ration conversion, and body weight. Important economic properties in broiler chickens include: egg fertility, hatchability, egg production and egg size.
The low value of heritability is not only due to low genetic variation, but is more determined by the high environmental variation. Heritability is one of the most important considerations in conducting animal evaluation, selection methods and mating systems. More specifically heritability is part of the total diversity of traits caused by genetic differences among the observed livestock. Heritability is a comparison between genetic variety to phenotypic variety.
Heritability is a term used to denote parts of the total diversity (as measured by variety) of a trait resulting from p) is the sum of the genetic variety of genetic influences. Variety of phenotypic (E).
In addition to the above description heritability can be interpreted in a broad and narrow sense. In a broad sense:
H2 = VG/VP
In addition to the broad sense of heritability can also be interpreted in a narrow sense as written in the formula:
h2 = VA/VP
The definition of heritability is divided into 2 senses, namely heritability in the broad sense is the total or summation between the genetic, dominant and epistatic varieties divided by the total or summation between the genetic, dominant, epistatic and environmental varieties. While heritability in a narrow sense, namely: Genetic variety per total or summation between genetic variety, dominant, epistatic and environment.
Heritability value can be calculated by comparing or measuring the relationship or similarity between the production of individuals who have kinship relationships.