A heritability of 0.5 indicates that one-half the phenotypic variance is attributable to genotypic variance, thus selective breeding has the potential to provide significant improvement the production trait. Note that 'Egg Quality' characters are often highly heritable, whereas 'Egg Production' traits under mass rearing are not. Likewise, 'Viability' characters show very low heritability: this indicates a large environmental influence, and for example that respiratory diseases are best approached as questions for sanitation or antibiotic treatment.