Consensus and debate in the definition of breeding objectives.

The breeding objective is usually to increase the profit of the firm, industry, or society that is investing in a breeding program. This objective should include long-term genetic gain and nonadditive genetic changes such as inbreeding depression and possibly a weighting against the variability of outcome. The breeding objective is described by a profit function that takes genetic values as input and produces profit as outcome. This profit function may be a bioeconomic model of the farm. The traits in the profit function should relate as directly as possible to all sources of income and costs. The profit function can include variables controlled by management decisions if these interact with genetic merit. The differences between genotypes should be evaluated when management variables are optimized for each genotype. In the long term, mean profit is expected to be close to zero, and all costs are assumed to be variable costs. Under these conditions, the relative economic weights are the same, regardless of how the farm is constrained how the unit for which profit is calculated, whether the perspective is that of individual producers, an industry, or consumers. However, if price signals are not passed along the chain from consumers to seed-stock breeders, the economic weights become distorted. The use to which breeding objectives are put, the perspective from which they are calculated, the rescaling and biological versus economic objectives, and the special problems associated with the inclusion of length of herdlife in the objective are discussed.