Heritability, repeatability, and genetic correlation of disease-resistance traits

Any successful genetic improvement program depends on the genetic parameters of heritability, genetic correlation, and repeatability. Heritability gives an indication for the variance of inheritance that is transmitted from one generation to the next. Heritability is usually low for disease-resistance traits, but indicator traits with high genetic correlation with disease traits have better heritability, which leads to better genetic gain. Somatic cell score for mastitis and fecal egg count for helminthiasis have high heritability with high genetic correlation with the disease trait and are effective for genetic improvement for respective traits. Different methods for heritability estimation have been discussed as offspring–parent regression, sib analysis, general linear model, and REML. The importance of estimated breeding value and repeatability are discussed. Examples with ketosis, mastitis, breech strike, and helminthiasis are discussed.