If the number of individuals per experimental unit varies, then we replace n in the equation above (which refers to a constant number of individuals per unit), with the harmonic mean of the number of individuals per experimental unit (nh) (Holland et al., 2003b; Nyquist, 1991).
Heritability of half-sib family means is simply a ratio of the variance component due to GCA and the phenotypic variance of half-sib family means: