Nr. 3 / 2007

Any breeding program should focus on maximizing the genetic gain. In our last generation of Atlantic salmon, Aqua Gen has implemented several improvements in the breeding program. These improvements give an annual increase in genetic gain of more than 33%, and will provide the customer with a better genetic material and a more uniform product from year to year.

In 2004, Aqua Gen merged its four breeding populations of Atlantic salmon into one. This new single breeding population will be reproduced during the autumn of 2007. The following changes were implemented in the breeding program in order to maximize genetic gain:

• Improved data quality
• Increased number of traits recorded
• Improved breeding structure
• Inclusion of data from several generations in the breeding value estimation
• Weighting of the different traits using industry based economic values
• Selection based on individual breeding values, instead of family breeding values
• Implementation of tools that help us to minimize inbreeding
• Reduction of the generation interval from four to three years

The factors that affect the rate of genetic change resulting from selection can be summarized in what is often called the key equation for genetic change (ΔG). In short, the key equation states that the rate of genetic change is directly proportional to three factors: accuracy of selection, selection intensity and genetic variation, and is inversely proportional to a fourth factor; the generation interval. Aqua Gen's new breeding program implemented on the new single breeding population of Atlantic salmon has focused on all four factors, and has resulted in an increased rate of genetic change.

Increased accuracy of selection

The accuracy of selection depends on both the data quality and how much information from relatives is available for the estimation of breeding values. For the last generation, the data quality has been improved by several means. These include a more concentrated and focused data harvest on all levels of production. This data harvest includes registrations of all families in all tests, the optimization of number of sibs tested, shorter data harvest periods and implementation of new technology (e.g. Q-Vision fillet scanner at slaughter test and ultrasound determination of sex). In addition, potential new traits for possible inclusion in the breeding program have been registered. For example;

• Resistance to piscirickettsiosis
• Fillet thickness
• Fillet weight
• Swimming performance as an indicator of cardiac fitness
• Vaccine side-effects
• Heart size and shape

In total, 17 traits that have been found to be heritable have been registered on the new breeding nucleus.

From this generation on, Aqua Gen has included phenotypes registered on halfsibs, parents and grandparents in the breeding value estimation. An improved breeding structure (partial factorial mating) has given us the opportunity to use information from maternal half-sibs in addition to paternal half-sibs in the estimation of breeding values. This additional information increases the accuracy of selection. Breeding values are estimated by multivariate analyses, meaning that the genetic correlations between the traits are accounted for.

In addition, ultrasound sexing of candidates increases the heritability and the precision of breeding values, because a fixed effect can be corrected for. The effect of sex is significant in most of the traits recorded.

Aqua Gen has always used full pedigree information back to the original wild Atlantic salmon in their breeding value calculations.

Increased intensity of selection

The selection intensity can be increased by either i) selecting a reduced number of individuals from a constant number of candidates, or by ii) selecting a constant number of individuals from an increased number of candidates. In our new breeding program, Aqua Gen has gone from family selection to individual selection. This means that we are not only selecting random fish from the best families, but also selecting the best candidates within the best families. In order to accomplish this, ultrasound sexing of juvenile breeding candidates took place after one year in sea. The sex of the selection candidate is needed for individual selection of fish at brood fish selection. Aqua Gen has further increased the selection intensity by increasing the number of families and the number of breeding candidates from each family available for selection.

Increased genetic variance

Aqua Gen‘s new breeding population has an increased genetic variance, attained by crossing four separate populations. Implementation of new software that helps us to maximise the genetic gain and at the same time control the rate of inbreeding, is an effective tool to prevent reduction of the genetic variance in the future. To avoid an unwanted rate of inbreeding Aqua Gen now selects the breeding candidates based on both breeding values and co ancestry coefficients. Aqua Gen is aiming to minimise the increase of inbreeding to <0.5 % per generation.

Reduced generation interval

The generation interval in the breeding nucleus has been reduced from four to three years. Reduction of the generation interval is a highly efficient measure to increase the genetic gain, and has increased the annual genetic gain in our population by 33%.

Economic weights

Aqua Gen has implemented economic value as a tool to weight the aggregated breeding value. The economic values are based on profit equations where changes in profit are due to genetic changes, not due to environmental changes or rescaling of the production. The model is based on an average salmon farm and inputs to it are provided by companies and official statistics.

 

PDF of the Information Letter is found here