Investigating growth curve of Najdi cattle using various non-linear equations

Abstract

Introduction: Traits related to growth are important economic traits in livestock, which are of
great importance in terms of economy and carcass performance. In order to describe the growth
curve in domestic animals, growth models are used, which provide a series of mathematical
functions consisting of a summary of animal growth information in the form of several
biological parameters.
Materials & methods: In this study, in order to investigate the growth curve of Najdi calves
in Khuzestan province, 7492 weight records from birth to two years of age of male calves and
7062 weight records of female calves in the same ages, collected until 2017 at the Najdi cattle
breeding station in this province, were used. The studied functions were Gompertz, Logestic,
Brody, VanBertalanfy and Richards. Regression models were fitted by an NLIN procedure in
the SAS software (ver. 9.1). The best fitted models were selected based on some criteria such
as the adjusted coefficient of determination, the mean squared error, the absolute mean residual
deviation and the bias corrected Akaike Information.
Results: Because the values of the examined criteria for the three models of Richards, Brody
and Vanbertalanffy were obtained the same in both male and female groups, approximately,
the Vanbertalanffy model (with fewer parameters) was proposed as a suitable function to
describe the growth curve from birth to one year old of age in male calves and from birth to 14
months old of age in female calves. Based on the appropriate model, the maturity weight and
the maturity rate were obtained as 330.2 and 380.8 kg, and 0.058 and 0.062 kg per month for
female and male calves, respectively. The ages and weights of female and male Najdi calves
were predicted as 9.7 and 11.7 month, and 94.28 and 104.57 kg, respectively. Also, the
estimated degree of maturity of studied female and male Najdi calves were obtained as 5.3%
and 5% of maturity weight at birth, 12.65% and 11.78% of maturity weight at 3 months of age,
and 18.97% and 17.91% of maturity weight at 6 months of age.
Conclusion: In conclusion, the proposed model can be applied to estimate the Najdi calves
growth and in feeding, fattening and breeding management.