Nigerian Fulani ecotype chickens - II – Estimation of growth curve parameters

In the study, growth curves of Nigerian Fulani ecotype chickens (NFEC) were modelled under two production systems with four non-linear  growth functions with a view to establishing growth descriptors for NFEC. Two hundred, day-old chicks of NFEC were  obtained from an established  population of NFEC. The chickens were separated randomly to intensive and pastured poultry production systems at 12 weeks of age. Data on body  weight were taken weekly over a period of 20 weeks. Four non-linear growth functions including Gompertz, Logistic, Bertalanffy and Richard's models were fitted using the NLIN procedure of SAS® while the best fit model was selected using the goodness-of-fit tests. For all the models, parameter (A), the asymptotic weight, ranged between 1800g and 2417g for male and 1208g and 1550g for female chickens respectively. Parameter  (B), the scaling parameter ranged from 0.77 and 19.79. Parameter K, which is the maturity index, ranged between 0.16 and 3.97 for both sexes. The R2 values ranged between 0.9689 and 0.9987 for all the models fitted. Gompertz and Bertalanffy models emerged as the best fit functions. Age and  body weight at inflection of NFEC were also predicted by the study. Growth curve parameters of NFEC in the pastured poultry system were not significantly different from those in the intensive system. The growth curve parameters estimated indicates that NFEC growth performance can be improved through effective breeding strategies and improved management practices. Keywords: Growth curves; modelling; descriptors; parameter