The dissemination of genetic improvement in salmon production

• Selecting specialized stocks for specific markets increased profit substantially.
• Most of the potential gain of selection was achieved by one step of selection.
• This strategy also adds flexibility to produce more specialized products.

A simulation study was conducted to investigate the potential advantage of two-step selection for dissemination of genetic gains in salmon production through a system with a nucleus breeding population, a multiplier tier and a grow-out tier. Results demonstrated that profit (measured in the grow-out tier in generation 8) can be substantially increased through production and dissemination of specialised stocks suited for e.g. specific production environments or markets. Truncation selection alternatives in two steps with varying selection proportions were compared to random sampling of parents in both dissemination steps: from the nucleus to the multiplier and from the multiplier to the grow-out tier. Strategies where truncation selection was used in one step and random sampling of parents in the other step were also tested. The selection alternatives with truncation selection in both steps gave on average between 31% and 26% higher profit than random selection. The selection alternative with an extremely low truncation selection proportion in two steps would on average give 2% higher profit than the selection alternative with extremely low truncation selection proportion from the nucleus to the multiplier (1st step), and a normally low truncation selection proportion from the multiplier to the grow-out (2nd step). However, the former alternative yielded five times fewer eggs. The study also showed that one step of truncation selection and one of random sampling of parents, irrespective of the order, would give on average about 19% higher profit compared to random selection in two steps. The effect of the correlation between the nucleus/multiplier breeding goal and the breeding objective of the grow-out was that profit was highest when the correlation was high. With a negative genetic correlation between the traits, profit was still high if the trait with the highest heritability (i.e. the trait measured on candidate itself) had the highest economic value. It was concluded that selection of specialised stocks for specific breeding objectives in two steps from the nucleus via the multiplier and to the grow-out could increase profit by 24%. Specific breeding objectives would also give more flexibility for a final product when the grow-out producers could ask for unique trait-combinations for their fish.