EVALUATION OF FOUR NONLINEAR MODELS DESCRIBING EGG PRODUCTION CURVE OF FAYOUMI LAYERS

Abstract

Egg production data used in this work were obtained from records of Fayoumi chickens flock belongs to El-Takamoly poultry project at Al-Azab, Fayoum Governorate. Egg production records over a 52-wk egg laying period related to 1900 hens. All data was summarized on a weekly basis as eggs per hen per week on hen-day (survivor) basis. Regarding Wood and McNally models, (a) stands for initial egg production, (a) parameter value was very low (0.001) for both models. The increasing rate to the egg production peak (parameter b) was 2.90 for the Wood model and 2.19 for the McNally model. Similarly, parameter c, the decreasing rate of egg production from the peak, was estimated to be 0.08 for the Wood model and 0.06 for the McNally model. Depending on compartmental function m, n, p and q represent scale parameter, measure of persistency of egg production, sexual maturity rate, and age at first egg, respectively and estimated values for these parameters were 86.47, 0.01, 0.23 and 21.61 wks of age, respectively, Concerning the modified compartmental model the parameters A, B, C and D represent a scale parameter, the rate of decrease in laying ability, the reciprocal indicator of the variation in sexual maturity and the mean age of sexual maturity of the hens, respectively. In this work the estimated values of the abovementioned parameters were 75.26, 0.006, 1.14 wks and 24.96 wks of age for A, B, C and D respectively. According to goodness of fit criteria, modified compartmental model was the best model for describing the egg-laying pattern of Fayoumi layers which had the lowest Akaike information criterion and Bayesian information criterion values and the highest coefficient of determination. Moreover, the modified compartmental model showed correspondence with the actual hen day of egg production (age and percentage at peak were 29.44 weeks of age and 64.16%, respectively).