Zoran LUKOVIÆ1,2

A random regression model (RRM) was applied to estimate dispersion parameters for number of piglets born alive (NBA) from first to tenth parity. Random regressions on Legendre polynomials of standardized parity were included for common litter environmental, permanent environmental and additive genetic effects. Estimated phenotypic variance and variance components (ratios) for NBA changed over parities and differed between farms. Eigenvalues for additive genetic effect were calculated in order to detect the proportion of additive genetic variability explained with individual production curves of animals. Existence of the 10-20 % genetic variability in the shape of the curves confirms a possibility for selection on persistency in litter size