Isotonic regression analysis of Guzerá cattle growth curves

Abstract

The objective of this study was to apply data transformation via isotonic regression in growth curves studies of Guzerá cattle whose data presented disturbances characterized by decreased body weight in certain age groups. Weight-age data were collected on newly weaned Guzerá males according to the methodology of weight gain tests (WGT) defined by the Brazilian Association of Zebu Breeders (ABCZ). The Logistic, Von Bertalanffy and Gompertz models were fitted to weight-age data using the generalized least squares method for non-linear regression models through the Gauss-Newton algorithm. The proposed transformation based on isotonic regression theory proved to be efficient; and the Logistic model was the best to describe the growth of animals, with a high percentage of convergence (100%) and goodness of fit assessed by the mean squared error (MSE) and the coefficient of determination (R2).

Growth curves of meat-producing mammals by von Bertalanffy’s model

“…This fact evidenced that for the description of growth characteristics of the group of animals under study, the parameterization and the value of m = 3/4 of great importance to obtain better fits. In practice, it is common to neglect the models with a practical or biological interpretation for parameter b, as in the studies of , Silveira et al (2011), Cassiano & Sáfadi (2015), Jacob et al (2015), and Rodrigues et al (2018). Nevertheless, if the parameterization of Model 3 is used, considering the correct allometry, a better fit can be achieved in these studies.…”

“…Curves of animal mass growth over time are shaped in S, which is also known as sigmoid or sigmoidal curves (von Bertalanffy, 1957). Several authors have reaffirmed that the body growth of most animal species can be described by a sigmoid curve and, therefore, fit by nonlinear models which are widely used for a large number of regression applications (Freitas, 2005;Carneiro et al, 2014;Teleken et al, 2017;Rodrigues et al, 2018).…”