It was evaluateddata set of 19,303 weight records of Santa Inês sheep in order to evaluatedistinct polynomial functions with different order for better adjustements offixed and random regressions of growth trajectory and to estimate (co)variancescomponents and genetic parameters of this trajectory. Fixed effects used inanalysis were contemporary group, sex and birth type. Ordinary and Legendrepolynomials, ranging from two to four orders, were evaluated for fixed regressionof average growth trajectory. Legendre and quadratic b-spline functions, rangingfrom three to four orders, were evaluated for random regressions. Legendre polynomialsof order fourth were suitable to fit random regression, while ordinary polynomialsof third order were the best for fixed trajectory. Direct heritabilities ondays 1, 50, 150, 250 and 411 were 0.24, 0.12, 0.44, 0.84, and 0.96, respectively,while maternal heritabilities for the same ages were 0.24, 0.19, 0.09, 0.02,and 0.01, respectively. Genetic correlations among weights in subsequent ageswere high, tending to unity, and there were negative correlations between weightsat early ages and weights at late ages. It is possible to modify the growthtrajectory by selection with the observed genetic variability. Genetic controlof weights at initial ages is not the same in late ages. So, selection of animalsfor slaughter in early age must be different from that of replacement animals.
