R. Bras. Zootec.13/Aug/2026;55:e20250022.
FiT: A software for adjusting the growth curve of animals
Ewerton Costa Sousa
, Leiliane Alves Soares da Silva
, Jonathan Lavor da Costa
, Lifranc Laurent
, José Lindenberg Rocha Sarmento
ABSTRACT
This paper aims to describe and evaluate FiT, a software that streamlines the process of analysing animal growth curves. It is characterized as a web-based software, developed using the Python and R languages, that adjusts the parameters of the classical nonlinear models Brody, Von Bertalanffy, Logistic and Gompertz. These parameters are estimated using the nlsLM function from the minpack.lm package of R. For model comparison, FiT calculates the mean square of the residuals, coefficient of determination, Akaike information criterion, and Bayesian information criterion. In addition, FiT determines the weights and ages at the inflection point (IP) and asymptotic point (AP), and displays graphs of the growth curve and its derivatives, highlighting the IP and AP. It is also possible to compare growth patterns considering different types of groupings. To evaluate the tool, the models were adjusted using growth data from Santa Inês sheep, and the estimated parameters and metrics were compared to those reported in other studies that used the same dataset. The results demonstrate its efficiency in performing animal growth curve studies, with emphasis on ease of use and the information generated from the estimated parameters. The FiT software is efficient for growth curve studies, easy to use, and provides additional information about the growth patterns in a short time and without the need for programming in statistical software.
