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Hello everyone. I welcome you to another lecture from the Animal Breeding module.

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Today we will talk about breeding value.

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The breeding value represents an estimation of the genetic merit of an individual

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and represents one of the basic genetic parameters used in livestock breeding.

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As was already said in previous lectures,

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the breeding of farm animals is based on the estimation of the genetic merit of the individual,

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which we obtain using the breeding value.

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The aim of breeding process is the breeder's profit,

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which is obtained through the animal's performance.

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The performance is affected by many factors,

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both environmental - which includes, for example, the external and internal environment,

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nutrition, and the breeder, but mainly by the individual's genetic,

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which, depending on the monitored trait, affects the given performance from 5 - 10%.

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The individual factors contribute to the overall performance in the following proportion:

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The influence of the breeder represents approximately 60% of the total variance of performance,

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random environmental influences from 30% and the genetic merit of the individual on average about 10%.

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Although the genetic merit represents a relatively small part of the total variance,

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it results in significant genetic progress and, consequently, better economics for the breeder.

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Breeding value has several definitions.

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The breeding value is always presented as an individual's deviation from the population mean.

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The definitions are based on the time concept of the possibility of determining the genetic merit of an individual.

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The first definition is based on testing of heredity,

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when the genetic value of an individual, mainly a sire,

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was determined based on the progeny performance.

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Another concept is based on understanding breeding value as the average effect

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of all genes that the progeny received from the sire or dam.

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The last definition is already based on a modern view of breeding value,

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when thanks to advanced computational and molecular genetic procedures,

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we can determine an individual's genetic merit based on its own performance.

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As mentioned in the previous slide, the Breeding Value always represents the additive genetic value

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of an individual expressed as a deviation from the population mean.


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Now, we will imagine the essence of breeding value.

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Here we will start from classical genetic theory,

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where we consider that the phenotypic value can be expressed as a function of genotype and environment.

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Further, genetic and environmental effects are expressed as a deviation from the population mean.

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The total genetic value can be divided into the additive genetic effect,

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the effect of dominance and effect of interaction, or epistasis.

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And since minor effects of dominance and epistasis are expected in purebred breeding,

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it is possible to express the genetic value of an individual only by the additive effect of genes.

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Breeding values, which represent an estimate of an individual's genetic merit,

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are therefore based on an estimation of the average additive effect of genes.

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We will explain why the breeding value is twice the deviation of the progeny performance

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from the population mean during random mating.

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Let's have a sire with the homozygous dominant genotype.

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This sire will be mated to a group of randomly selected dams

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in which we expect all genotypes to be represented.

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As we know, this sire can produce only one type of gametes,

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and that only with a dominant allele; on the contrary,

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a group of dams produces all kinds of gametes, in this case, gametes with a dominant and a recessive allele.

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If the gametes fuse, all genotypes will be represent in the offspring population.

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Because the mothers were selected randomly, we expect the effect of the mother on offspring performance to be zero.

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The effect of offspring deviation from the population mean is attributed to the sire.

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But as it is clear from the picture, the sire contributes only half of its genotype to the offspring - only one allele.

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To get the whole genetic effect of the sire, we must multiply the deviation by two.

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Hence, double the progeny performance deviation from the population mean during random mating.

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As mentioned, breeding value is defined as the average of genetic effect of an individual's genes.

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Since the breeding value includes only the additive effect of genes, it is possible to use

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it to estimate the genetic merit of the offspring of selected parents and vice versa.

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it is because the average genetic value of the parents corresponds to the average genetic value of their offspring.

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Conversely, we can also estimate the parent's average genetic value from the offspring's average genetic value:

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each offspring receives 50% of its genes from each parent.

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The conclusions from the previous slide can also be used to estimation the average progeny performance,

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with adding the average breeding values of the sire and dam to the population mean.

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But this formula is only valid for a large group of offspring, not for a single offspring.

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And this is because, in the case of one offspring, it is also necessary to put the so-called

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"Mendelian sampling" in the formula.

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The effect of Mendelian sampling will be introduced here. Consider two mating individuals.

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Both individuals produce two types of gametes.

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Suppose four full-sibs are born, for example, in one litter. According to the classical approach,

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we expect the average relatedness of these offspring to be equal to the value 0.5.

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However, if we look at the picture, we will find that offspring 1 and 2 have identical genetic merit, 

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while individuals 1 and 4, on the other hand, are genetically unrelated.

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If we averaged the relatedness across all full-sibs, we would get an expected value of 0.5, as noted.

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Mendelian sampling, therefore, represents the randomness of which type of gametes will receive a new offspring.

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Therefore, we cannot determine one offspring's expected performance thanks to Mendelian sampling.

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But for a large group of offspring, the effect of Mendelian sampling cancels out because, on average, the offspring match the expected values.

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Therefore, we can predict the performance with relatively high reliability for a large group of progeny .

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Breeding value is always only an estimate or a prediction.

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It is because we are not yet able to determine the exact genetic merit of an individual and the effect of all genes of an individual.

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And this estimate is expressed as the individual's deviation from the population average -  directly as the individual's deviation by own performance

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or as twice the deviation of the average progeny performance during random mating, the so-called test mating.

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This test mating was mainly used for performance that we cannot directly measure for individuals - for example,

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the prediction of the genetic merit for the milk yield of sires in dairy cattle.

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The only way to obtain exact values of an individual's genetic merit would be if the monitored trait has a coefficient of heritability equal to 1

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or if the individual testing was based on an infinitely large group of progeny.

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Unfortunately, both conditions for quantitative traits are unrealistic in practical breeding.


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Estimation of breeding value is possible based on these sources of information and their mutual combination:

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performance of the ancestor, own performance, performance of full-sibs or half-sibs, and progeny performance.

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An estimate of breeding value is obtained using the following formula.

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The breeding value is expressed as an individual's deviation from the population mean.

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It is a regressed relationship, represented by the value of the regression coefficient "b".

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This regression coefficient takes on a value based on the performance source, with which we estimate the individual's genetic merit.

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The table also shows the relationships for obtaining individual values of the regression coefficient „b“.


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Since the breeding value is an estimate, it is necessary to quantify the accuracy or reliability of this breeding value.

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The accuracy of the breeding value, is presented by "r", represents the relationship (correlation) between the estimated breeding value

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and the true genetic value of the individual.

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The reliability of the breeding value, which is presented as "r2", is expressed by the coefficient of determination.

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The reliability describes how many per cent of the true genetic value of the individual is explained by the estimated breeding value.


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We will show the explanation of the term accuracy in the following figures.

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Let's have a group of, for example, 1000 individuals. Every individual is presented as a point in the graph.

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On the y-axis, we plotted the true genetic merit of the individual.

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On the x-axis we have the predicted breeding value.

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Let's assume the accuracy of the estimation of the breeding value for the given population is one per cent, which is a value of 0.01.

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If we were to select the top 10% of individuals based on breeding value, we would choose only the four individuals with the best genetic merit.

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In this graph, these individuals are marked in green.

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Individuals marked in black are individuals that have been estimated to have a high breeding value, but their actual genetic merit is average or low.

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On the contrary, individuals marked in red are individuals with the best genetic merit but with an estimated average or low breeding value.

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The graph shows that if the accuracy value of the breeding value is low, the predicted breeding value does not correspond very well to the genetic merit of the individual.


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If the accuracy of the breeding value is equal to 0.5, we would already have selected a more significant proportion of individuals with the best genetic merit.


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And with an accuracy value equal of 0.8, we are already selecting most of the correct individuals based on the breeding value prediction.

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These graphs, therefore, show a significant influence of the breeding value accuracy parameter on the selection response or genetic gain.

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If, based on breeding value, we wrongly select individuals with below-average genetic makeup, the response to selection cannot reach high values.


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This lecture presented the concept of breeding value and its influence on breeding programs.

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Thank you for your attention, and I look forward to seeing you in the following video. Bay.