Autores

Ênio Contini, Elisa Junqueira Oliveira, Ricardo Lopes Dias Costa, Gabriela Geraldi Mendonça, Aníbal Eugênio Vercesi Filho , Flavia Fernanda Simili, Lenira El Faro, Claudia Cristina Paro de Paz

Adjustment of non-linear models for growth in Morada Nova sheep breed

Resumo

Performance evaluation of adapted animals to local conditions for economic traits is essential
for the preservation of species and
their genetic resources. The size of Morada Nova breed herds have decreased over time,
becoming restricted to a few regions.
Other races have been used with higher frequency because of their production
and adaptation, and are important as a
source of food and income for
local communities. The objective of this research
was to evaluate the application of nonlinear models to describe the growth
curve of Morada Nova sheep. Records of 1604 weights of 250 lambs from Nova
Odessa municipality, being 934 repeated measurements of female and 670 repeated
measurements of male, obtained between 2012-2013 were used. The
average birth weight observed was 2.50 ± 0.690 kg. The nonlinear models used to adjust the data were Brody Yt = A (1 - be^{-kt});
Von Bertalanffy Yt = A (1 - be^{-kt})^{3}; Richards Yt = A (1 -
be^{-kt})^{m}; Logistic Yt = A (1 + e^{-kt})^{-m}
and Gompertz Yt = Ae ^{-be(-kt)}. The models were
fitted by Gauss-Newton using the NLIN procedure of SAS (SAS Inst., Inc., Cary, NC).
The parameters that make up the
functions are Y = body weight at the age t; A = asymptotic weight that represents the average adulthood weight; K = Maturation rate, an indicator of the speed with which the animal approaches its adult size, maturity of
the individual in relation to age is the fraction of mature weight attained by the individual at this age; B = Integration constant which is
related to the initial weights of
the animals and reflects the degree of maturation at birth (t = 0); m = Curve shape definition and
thus determines at what
proportion of the asymptotic
value (A) the inflection point
of the curve occurs. Only the
model of Richards did not reach convergence. The quality of fit of the models
was verified by the predicted mean error (PME - lower, better the fit,
indicating a smaller difference between the observed and estimated weights);
the predicted mean error of the models was: Bertalanffy -18.997 ± 1.97, Brody
-48.209 ± 2.09, Gompertz -15.787 ± 1.31, Logistic 13.623 ± 1.23. Despite the
logistic model have shown the lowest average predicted error, this model
underestimated the weight for the entire curve. The use of the Gompertz model
can be indicated to adjust the growth curve of the Morada Nova breed animals
because model only overestimated the birth weight the birth, which can be
explained by the smaller number of data in the first days of animals life of
the animals.

Ajuste de modelos não lineares para o crescimento em ovinos da raça Morada Nova

Abstract

Íntegra (PDF)