Comparison of two non-linear functions describing the growth of Popielno White and New Zealand White rabbits

The objective of this study was to compare growth curves of Popielno White and New Zealand White rabbits modelled by the von Bertalanffy and Gompertz functions. There were 37 Popielno White (21 males and 16 females) and 55 New Zealand White (28 males and 27 females) rabbits used. The nonlinear regression procedure (NLIN) in the SAS 9.4 software (SAS, 2014) was used for modelling rabbits growth curves from birth to 12th week of age. To see how the process of rabbit growth might run in next weeks, we extrapolated weights of rabbits up to 30th week of age. Six criteria: the mean error, mean squared error, mean absolute error, quotient between the error sum of squares and the observed sum of squares, corrected Akaike Information Criterion and Bayesian Information Criterion were used to compare models. The shape of all curves was sigmoid and both models well fitted to data from birth to 12th week of age, i.e. during interpolation process. The problem with the fit occurred later, during extrapolation process, i.e. when models were used to predict the course of the growth of animals in the next weeks of age. When body weight was extrapolated in later weeks of rabbits life, we noticed slightly worse fitting of von Bertalanffy model and overestimation of the asymptotic body weight of animals. To predict the further course of rabbit growth in practice, the Gompertz function would be a better choice. Additionally the Gompertz model could be a helpful tool for breeders to describe growth process of rabbits and to select a more economically profitable breed.

