Crescimento ponderal e biométrico de poedeiras leves por meio do modelo de Gompertz : modelagem das variâncias e densidades de criação

Abstract

The objective was to predict the ponderal and biometric growth of lightweight laying hens through the Gompertz model and modeling of the variances. For this, two experiments were conducted. In the first experiment, with lasting 112 days, for start phase (1 to 14 days of age), 2500 one-day-old female chicks (Hyline W-36) were weighed individually and distributed, in a completely randomized experimental design, in five densities of 100.00; 105.66; 112.00; 119.15 and 127.27 cm2 /bird, with ten repetitions each. For the rearing phase (15 to 112 days old), 750 pullets (Hyline W-36) were weighed individually and distributed in a completely randomized design in five densities of 294.74; 329.41; 373.33; 430.77 and 509.09 cm2 /bird, with ten repetitions each. The birds were given rations formulated to meet the nutritional requirements of each phase, with ration and water provided ad libitum. The Body mass and age data of lightweight laying hens reared at different population densities were obtained at 1, 7, 14, 21, 28, 42, 56, 70, 84, 98, and 112 days of age. The statistical analyses were performed in the SAS (Statistical Analysis System, University Edition) software, through the procedure for mixed nonlinear models, with the level of significance established at p<0.01, in all analyses. In the second trial, 280 one-day-old female chicks (Hyline W-36) were distributed in metal cages and accompanied until 140 days old. For the adjusted rearing density, the experimental period was divided into three stages from 1 to 14; 15 to 112 and 113 to 140 days of age. The rations were formulated to meet the requirements of the birds. The ration and the water were made available ad libitum. Weekly, all the birds in the cages were weighed. From these, five birds with average weight were selected and employed in the analyses. The birds were sacrificed by cervical dislocation and then samples of feathers were collected. The collection of feathers followed evisceration directed at organ biometry. The data observed from 1 to 140 days of the age of lightweight laying hens were used in the analysis. In experiment 1, from the results of the evaluations of the multi models obtained by the combination of Gompertz and functions of variance, it is concluded that to describe the growth of lightweight laying hens in different densities, the model of Gompertz and function of staggered variance, common for the densities of rearing, better explain the behavior of the variance for body mass the birds. In the significance check analysis of the parameters in the different densities, the estimates of the averages of the parameters of asymptotic mass, growth rate, and time (days) were not interfered with by the different densities rearing of lightweight laying hens. Growth curves of lightweight laying hens in different densities, adjusted and graphically illustrated through the unanimous model, have a sigmoid aspect and those adjusted through the derivative, detail the increases in mass gains. In experiment 2, in the evaluations of multi models obtained by combining the Gompertz model and the association of functions of variance, for more than half of the dependent variables, the unanimous model was Gompertz and function of stepped variance. Thus, it is concluded that to describe the growth of body, feather, and organs of lightweight laying hens, the Gompertz model and function of staggered variance better explain the behavior of variance of the variables body mass with or without feathers, feather mass, liver mass, proventriculus mass, heart mass, and total large intestine, while the function of exponential variance better elucidates the behavior of variance of the variables gizzard, total small intestine, and pancreas of birds. Body growth curves, of feather and organs of lightweight laying hens, adjusted and graphically illustrated through the respective unanimous model, present sigmoid aspect and those adjusted through the derivative, detail the mass gains for each variable.