Economic accounting of numbers of expressions and delays in sheep genetic improvement

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Abstract
Formulae were developed which use discounted gene‐flow principles to help quantify the economic value of genetic superiority in individual rams or ewes. Modifications allow discrimination among situations with terminal versus self‐replacing ewes and rams and among traits expressed in ewes or lambs at different ages. Results are presented in terms of discounted genetic expressions. These can be multiplied by the economic value of a change in a specific trait when weighting selection indexes or conducting cost‐benefit analyses of breeding strategies. In the base situation, numbers of discounted genetic expressions were 182 and 232 for lamb slaughter traits from a terminal sire ram, and from a ram breeding self‐replacing ewes, respectively. For annual ewe traits such as number of lambs born and wool production, numbers of discounted genetic expressions were 167 and 239 from rams breeding terminal and self‐replacing ewes, respectively. Results of calculations were also shown for breeding females and for lamb traits at birth and traits expressed by ewe hoggets and by ewes at culling. The effects of alternative values for variables used in the formulae were tested using sensitivity analysis.