Comparação de alguns modelos matemáticos para ajuste à curva de lactação média de um rebanho da raça Caracu
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Data
1999-01-01
Autores
El Faro, Lenira
Albuquerque, Lucia Galvão de [UNESP]
Fries, Luiz Alberto
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Brasileira de Zootecnia
Resumo
No presente estudo foi estimada a curva de lactação média de 7239 lactações de vacas da raça Caracu, com base em 299.949 controles semanais. As funções ajustadas aos dados médios da curva de lactação foram Linear Hiperbólica e Quadrática Logarítmica, como lineares, e Gama Incompleta e Polinomial Inversa, como não-lineares. Os parâmetros foram estimados por meio de processos iterativos, método de Gauss-Newton. O Coeficiente de Determinação ajustado (R²A), o Teste de Durbin-Watson (DW) e os desvios (%) entre as produções totais (PTL) observadas e estimadas foram usados como medida da qualidade do ajuste. Os resíduos estimados, apesar de pequenos, apresentaram correlação serial positiva, pois o teste DW foi significativo para as quatro funções estudadas, indicando violação da pressuposição de independência entre estes resíduos. Os R²A foram superiores a 97% e os desvios entre as PTL observadas e estimadas, mínimos, indicando que, de acordo com estes critérios, qualquer função poderia ser usada para ajustar a curva de lactação média desse rebanho. Quanto aos componentes da curva, a melhor aproximação foi obtida pela função Polinomial Inversa, para produção inicial, tempo e produção no pico. As funções Gama Incompleta e Quadrática Logarítmica apresentaram ajustes semelhantes, porém a primeira apresentou melhor definição dos parâmetros e componentes da curva de lactação.
The present study was carried out to estimate the average lactation curve of 7239 lactations of Caracu cows based on 299,949 weekly records. The functions fitted to the mean data of the lactation curve were: Linear Hyperbolic and Logarithmic Quadratic as linear and Incomplete Gamma and Inverse Polynomial function as non-linear. The parameters were estimated by iterative methods, Gauss-Newton method. The adjusted Coefficient of Determination (R²A), the Durbin-Watson test (DW) and the deviations (%) from actual and predicted total milk yield were used as measurement of goodness of fit. The estimated residues, even though small, presented a positive serially correlation because the DW test was significant for the four studied functions, indicating violation of the assumption of the independence among the residues. The R²A were higher than 97%, and the deviations between actual and predicted milk yields were small, indicating that, in accordance with this criterion, any function could be used to fit the average lactation curve of the herd. Regarding to the components of the lactation curve the best approach was obtained by the Inverse Polynomial function for initial production, time and production on peak. The Incomplete Gamma and Logarithmic Quadratic functions presented similar adjustment, however, the first one presented better definition of parameters and components of the lactation curve.
The present study was carried out to estimate the average lactation curve of 7239 lactations of Caracu cows based on 299,949 weekly records. The functions fitted to the mean data of the lactation curve were: Linear Hyperbolic and Logarithmic Quadratic as linear and Incomplete Gamma and Inverse Polynomial function as non-linear. The parameters were estimated by iterative methods, Gauss-Newton method. The adjusted Coefficient of Determination (R²A), the Durbin-Watson test (DW) and the deviations (%) from actual and predicted total milk yield were used as measurement of goodness of fit. The estimated residues, even though small, presented a positive serially correlation because the DW test was significant for the four studied functions, indicating violation of the assumption of the independence among the residues. The R²A were higher than 97%, and the deviations between actual and predicted milk yields were small, indicating that, in accordance with this criterion, any function could be used to fit the average lactation curve of the herd. Regarding to the components of the lactation curve the best approach was obtained by the Inverse Polynomial function for initial production, time and production on peak. The Incomplete Gamma and Logarithmic Quadratic functions presented similar adjustment, however, the first one presented better definition of parameters and components of the lactation curve.
Descrição
Palavras-chave
lactation curve, persistency, Milk production, Curva de lactação, Persistencia, Leite - Produção
Como citar
Revista Brasileira de Zootecnia. Sociedade Brasileira de Zootecnia, v. 28, n. 5, p. 987-992, 1999.