Classical nonlinear models to describe the growth curve for Murrah buffalo breed/Modelos nao-lineares classicos para descrever a curva de crescimento de bufalos da raca Murrah

With the objective of to adjust nonlinear models for the growth curves for a buffaloes herd raised in floodable lands in Rio Grande do Sul state, monthly records measured from birth to two years-old of 64 males and 63 females born between 1982 and 1989 were used. The models used were: Von Bertalanffy, Brody, Gompertz and Logistic. The parameters were estimated by NLIN procedure and the criteria used to evaluate the adjustment given by the models were: asymptotic standard deviation; coefficient of determination; average absolute deviation of residues and asymptotic index. Von Bertalanffy and Brody models overestimated the male asymptotic weight (A) in 15.9 and 171.3kg, respectively, and the Gompertz and Logistic models underestimated it in 4.5 and 13.4kg, respectively. For females, the Logistic model underestimated the asymptotic weight (-2.09kg), and Gompertz, Von Bertalanffy and Brody overestimated this parameter in 8.04, 17.7, and 280.33kg, respectively. The biggest average deviation was estimated by Brody model for both sexes, characterizing the biggest index. Considering the criteria, it is recommended the Gompertz and Logistic models for adjust females and males Murrah buffaloes breed growth curves. Key words: asymptotic weight, buffalo, maturation rate. Com o objetivo de ajustar modelos nao-lineares ao crescimento ponderal para bufalos criados em terras baixas no Estado do Rio Grande do Sul, foram utilizados registros mensais mensurados do nascimento aos dois anos de idade de 64 machos e 63 femeas, nascidos no periodo de 1982 a 1989. Utilizaram-se os modelos: Von Bertalanffy, Brody, Gompertz e Logistico. Os parametros foram estimados usando o procedimento NLIN e os criterios utilizados para verificar o ajuste dos modelos foram: desvio padrao assintotico; coeficiente de determinacao; desvio medio absoluto dos residuos e o indice assintotico. Os modelos Von Bertalanffy e Brody superestimaram o peso assintotico (A) para os machos em 15,9 e 171,3kg, respectivamente, e os modelos Gompertz e Logistico, subestimaram em 4,5 e 13,4kg, respectivamente. Para as femeas, o modelo Logistico subestimou o peso assintotico (-2,09kg) e os modelos Gompertz, Von Bertalanffy e Brody superestimaram esse parametro em: 8,04; 17,7 e 280,33kg, respectivamente. O maior desvio medio absoluto foi estimado pelo modelo Brody para ambos os sexos, caracterizando o melhor indice. Considerando os criterios, recomenda-se o modelo Gompertz e o modelo Logistico para ajustar a curva de cr