Data set of 17.767 weight records of 4.210 Santa Inês lambs were used aiming to evaluate the importance of the inclusion of the maternal effect in the model to estimate components of (Co) variance and resulting genetic parameters for the growth curve through random regression models. The fixed and random regressions were fitted using Legendre Polynomials of order three, being fit four models that differed in relation to the inclusion of the additive genetic and permanent environmental maternal effects. Considerable increase was observed in Log L and decrease in the criteria AIC and BIC when the maternal effect was included (genetic or permanent environmental), evidencing its importance. The maternal genetic effect explained larger proportion of the phenotypic variance than the maternal permanent environmental along the growth curve. The direct additive genetic variance was inflated by maternal effect, when this last one was not considered in the analysis model, reflecting the same behavior in the heritabilities. The maternal permanent environmental effect contributed to maternal variance, as well as, it inflated maternal genetic variance, when it was not considered in the model. Similar behavior was verified with maternal heritability. The correlation estimated for the four models hardly differed in function of maternal effect. The maternal effect should be considered in the genetic studies of the growth curve of Santa Inês sheep.Utilizaram-se 17.767 registros de pesos de 4.210 cordeiros da raça Santa Inês com o objetivo de avaliar a importância da inclusão do efeito materno nos modelos de estimação de componentes de (Co)variância e parâmetros genéticos resultantes para a curva de crescimento, por meio de modelos de regressão aleatória. As regressões fixas e aleatórias foram ajustadas por meio de polinômios de Legendre de ordem três, testando-se quatro modelos que diferiram quanto à inclusão dos efeitos genético aditivo materno e ambiente permanente materno. Observou-se considerável aumento no Log L e diminuição nos critérios AIC e BIC quando se adicionou o efeito materno (genético ou ambiente permanente), evidenciando sua importância. O efeito genético materno explicou maior proporção da variância fenotípica que o ambiente permanente materno ao longo da curva de crescimento. A variância genética aditiva direta estimada foi inflacionada pelo efeito materno, quando este não foi incluído no modelo de análise, refletindo o mesmo comportamento nas herdabilidades. O efeito de ambiente permanente materno contribuiu para a variância materna, como também, inflacionou variância genética materna, quando não foi considerado no modelo. Comportamento semelhantemente foi verificado com a herdabilidade materna. As correlações entre pesos nas diferentes idades estimadas pelos quatro modelos praticamente não diferiram em função da modelagem do efeito materno. O efeito materno deve ser considerado nos estudos genéticos da curva de crescimento da população em estudo.Maternal effect or growth curve of Santa Inês sheep by random regressionmodelsAbstractData set of 17.767 weight records of 4.210 Santa Inês lambs were used aiming to evaluate theimportance of the inclusion of the maternal effect in the model to estimate components of (Co)variance and resulting genetic parameters for the growth curve through random regression models.The fixed and random regressions were fitted using Legendre Polynomials of order three, being fit fourmodels that differed in relation to the inclusion of the additive genetic and permanent environmentalmaternal effects. Considerable increase was observed in Log L and decrease in the criteria AIC andBIC when the maternal effect was included (genetic or permanent environmental), evidencing itsimportance. The maternal genetic effect explained larger proportion of the phenotypic variancethan the maternal permanent environmental along the growth curve. The direct additive geneticvariance was inflated by maternal effect, when this last one was not considered in the analysismodel, reflecting the same behavior in the heritabilities. The maternal permanent environmentaleffect contributed to maternal variance, as well as, it inflated maternal genetic variance, whenit was not considered in the model. Similar behavior was verified with maternal heritability. Thecorrelation estimated for the four models hardly differed in function of maternal effect. The maternaleffect should be considered in the genetic studies of the growth curve of Santa Inês sheep.