Stiffness, used for grading logs, is positively correlated with growth strain with a correlation of 0.61, an unfavourable correlation requiring a trade-off between the two traits.
A strong, unfavourable correlation between growth strain and stiffness indicates that tree selection will have to deal with a trade-off between those traits when breeding for overall wood quality in E. bosistoana.
These QTLs, along with those specific for seed content identified on LGs 2, 6, 10, 13 and 15, might allow to dissociate the unfavourable correlation between berry size and seedlessness in breeding programs.
However, current breeding objectives are indirectly affecting adaptation given the unfavourable correlations between resilience and production traits (e.g. West, 2003).
Because of unfavourable correlations between androstenone and other sex steroids [ 4], a direct selection against high levels of androstenone would result in decreased production of testosterone and estrogens, with associated negative effects on performance and sexual maturation.
However, it is difficult to make appreciable genetic progress by traditional breeding methods because the heritability of the trait is low (Heringstad et al. 2000; Hansen et al. 2002; Carlén et al. 2004) and there is unfavourable genetic correlation with production traits (Lund et al. 1999; Carlén et al. 2004).
If answering this question would provide information concerning the underlying mechanisms controlling the traits, it would also provide information about whether an unfavourable genetic correlation between two characters can be broken (in the case of linkage) or whether this is impossible (in the case of pleiotropism).
Nevertheless, based on to the unfavourable genetic correlation between direct and maternal effects that we have evidenced in this study for A, B and P, it will be difficult to select sires that will both contribute to improving the FE of the mares mated with them and the FE of their daughters.
However, a serious breeding concern is that estimates from a number of studies present unfavourable genetic correlations, on average near 0.3, between various fertility measures and production [ 8].
Low heritabilities of linear and quadratic regression coefficients and their unfavourable genetic correlations with other performance traits reveal that altering the shape of the feed intake curve by direct or indirect selection is difficult.
The ATLAS Score - known for its ability to predict the unfavourable outcome correlated directly, statistically significant, with the Charlson comorbidity index (weak correlation) (r = 0.356, p <0.001) and with the age-adjusted comorbidity index (medium correlation) (r = 0.505, p <0.001).
