Polynomial functionsof age of different orders were evaluated in the modeling of the average growthtrajectory in Santa Ines sheep in random regression models. Initially, the analyseswere performed not considering the animal effect. Subsequently, the random regressionanalyses were performed including the random effects of the animal and its mother(genetic and permanent environment). The linear fit was lower, and the otherorders were similar until near 100 days of age. The cubic function providedthe closest fit of the observed averages, mainly at the end of the curve. Orderssuperior to this one tended to present incoherent behavior with the observedweights. The estimated direct heritabilities, considering the linear fit, werehigher to those estimated by considering other functions. The changes in animalranking based on predicted breeding values using linear fit and superior orderswere small; however, the difference in magnitude of the predicted breeding valueswas higher, reaching values 77% higher than those obtained with the cubic function.The cubic polynomial function is efficient in describing the average growthcurve.
