Genetic Correlations
Genetic correlations for longevity traits expressed in organic and conventional dairy production systems in Sweden are close to unity, except for fertility determined survival in the Swedish Red breed which is significantly different from unity. The reason for this low correlation is not clear. Genotype by environment interactions do not exist for fertility traits in this breed (Sundberg et al., 2010), indicating that the same genes are important for fertility in both production systems. Still, the G×E found in this study indicates that different genes are important for fertility-determined survival,which may indicate differences in farmers’ culling criteria. Whether correlations of this magnitude (0.80) are low enough to justify development of a separate breeding program for organic production depends on population size, the structure of the breeding program and its cost (Nauta, 2009).