Non-linear mixed models in the study of growth of naturalized chickens

Vicente Ibiapina,Firmino José Vieira Barbosa,José Elivalto Guimarães Campelo,José Lindenberg Rocha Sarmento

doi:10.37496/rbz4920190201

Abstract

ABSTRACT This study was conducted to examine the inclusion of random effects in non-linear models, identify the most suitable models, and describe the growth of naturalized chickens. Live-weight records of 166 birds of the Grauna Dourada, Nordestina, and Teresina ecotypes were estimated. The asymptotic weight (A), integration constant, related to animal initial weight (B), and the maturing rate (k) parameters of the non-linear Gompertz, Logistic, and von Bertalanffy models were estimated and adjusted using the Gauss-Newton method. Residual variance decreased [...]

Highlights

Chickens were introduced in Brazil at the time of its discovery and colonization
The best fits in the estimate of the growth curve of females were obtained by associating the random effects with the three parameters of the Gompertz and Logistic models
The Gompertz model with random effects associated with the A and k parameters estimated similar asymptotic weights between the two sexes

Summary

Introduction

Chickens were introduced in Brazil at the time of its discovery and colonization. The chicken groups that were not subjected to any breeding method and that adapted to the rearing conditions and to the environment in which they were managed were named “naturalized” chickens.Several ecotypes of the species were extinguished after the introduction of genetically improved breeds and lines from other countries. The chicken groups that were not subjected to any breeding method and that adapted to the rearing conditions and to the environment in which they were managed were named “naturalized” chickens. Non-linear models allow for a comparison of the growth curve of different genetic groups, making it possible to evaluate differences in animal growth caused by sex, management, and rearing environment. They provide essential information to guide the sustainable preservation of animals at risk of extinction, such as the estimate of nutritional requirements and growth (Hruby et al, 1994; Selvaggi et al, 2015)

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