The organic share of Swedish dairy production is steadily increasing and represented almost 6% of the market in 2007 (Swedish Ecological Farmers Association,2008). However, organic farmers in Sweden, as in most other countries, are dependent on conventional breeding programs. Longevity is considered in the Swedish breeding goal and the genetic trend is positive,in contrast to the international trend (Mark et al.,2005). Nevertheless, genetic progress may be limited in organic production if genotype by environment interaction (G×E) exists between organic and conventional production environments; that is, if different genes are important in the different production systems. The main differences between organic and conventional dairy production, which may generate G×E, are related to feeding regimens and medical treatments. These differences are described in detail by Sundberg et al.(2010). Genotype by environment interactions can result in different scaling between the environments (i.e.,the difference between animals varies) or in reranking of bulls between the environments. Occurrence of G×E is often analyzed as a genetic correlation different from unity, between 1 trait expressed in 2 different environments (Falconer and Mackay, 1996).