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1) Hello, and welcome to another video from the Animal Breeding module,

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where we will be looking at practical examples for the Selection Effect, or Genetic Gain.

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2) We have to estimate the level of selection effect for two different breeding strategies

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when we have a dairy cattle population of 30,000 heifers available each year.

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From these cows we select for further breeding: 18 000 cows as cow mother or 1 500 cows as bull mother.

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We know the following population parameters for milk production σ P = 600 kg, h2 = 0,25.

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We have to estimate the level of the estimated selection effect for both strategies and compare them.

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3) To predict the selection effect, we use the formula given here.

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The only information we don't have at the moment is the value of the selection intensity.

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The other two parameters heritability coefficient and phenotypic standard deviation were specified in the example.

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In order to estimate the selection intensity we need to know the value of the proportion of selection.

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And since we are selecting 18000 individuals out of 30000 individuals, the sekection proportion takes the value of 0.6.

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The tabulated value of the selection intensity corresponds to 0.6439.

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4) If the value of the selection intensity is added to the formula,

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we obtain the value of the expected selection effect in such a selected population,

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which is equal to 96.59 kg of milk per lactation.

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6)In the second example, when we select bull mothers,

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it is obvious that the number of bull mothers should be lower because due to artificial insemination,

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and lower number of sires and therefore their mothers are needed to ensure reproduction.

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In the case of bull mothers, the selection poportion is only 5%.

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The value of the selection intensity found in the tables is 2.0628. 

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6) When all values are included into the above formula,

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the expected selection effect is 309.42 kg of milk per lactation.

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Because we select a smaller number of better individuals,

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the selection intensity reaches higher values than in the previous case

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and therefore the selection effect has a higher value.

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7) We have to estimate the level of selection effect for a planned strategi,

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when breeders are considering whether to set up a performance test station for selection of bulls mothers.

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In this station test, it would be possible to increase the coefficient of heritability

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for milk production to h2 = 0.49 by standardizing environmental conditions.

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Genetic variability would be the same in both the field and station tests (σA = 300 kg).

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The breeders will select 3000 individuals for the test each year.

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Also in the station test, 1500 bulls mother would need to be selected each year for further breeding.

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8) In this case, we use the following formulas to estimate the level of the selection effect.

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When data on genetic variance and breeding value accuracy were provided in the example.

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To estimate the selection effect, we still need to find the value of the selection intensity.

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9) The intensity of selection is again obtained using the tables

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and the value of the proportion of selection.

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The breeders include 3000 cows in the test and select 1500 future bulls mothers.

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The proportion of selections is therefore 50%. This corresponds to a selection intensity value of 0.7979.

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When all the values are added to the relationship, we obtain a selection effect value of 167.56 kg.

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10) The table here shows all estimates of selection effects.

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The highest selection effect is obtained from the field test when selecting bull mothers.

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Due to highest level of selection intensity

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The second highest selection effect is estimated for the test station,

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where we obtain the highest value of the coefficient of heritability,

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but we do not obtain a high value of selection intensity.

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The lowest expected selection effect would be estimated for the selection of cow mothers,

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which showed the lowest value of selection intensity and a lower value of heritability coefficient.


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11) Thank you for your attention and I look forward to seeing you again at the next video.