Determination of Phosphorus Requirement for Post Molted Laying Hens using Nonlinear and Multivariate Nonlinear Mixed Effects Models

An experiment was conducted to determine the available phosphorus (AP) requirement for post molted laying hens by using the broken line models, logistic model, saturation kinetics model and multivariate nonlinear mixed effects models. The experiment was conducted as a randomized complete block design with 5 dietary treatments (1, 1.5, 2, 2.5 and 3 g/kg of diet AP) and 6 replicates in each (72 hens per treatment). Hens were fed the experimental diets from 85 to 102 wk of age. Feed consumption and egg production were recorded daily, whereas body weight was obtained at the start of 85 and at the end of 102 wk of age and BW changes were calculated. Weekly, 1-d egg production weight was measured and egg mass was calculated. Egg qualities were measured at the end of 102 wk of age. According to the results, the optimal AP requirement from 85 to 102 wk of age for egg production, feed efficiency, egg mass, egg weight, average daily feed intake, shell breaking strength, shell thickness, egg shell percentage and BW changes were 2.1, 2.4, 2.1, 2.5, 1.8, 2.3, 2.1, 2.4 and 2.2 g/kg, respectively. The logistic model only was fitted to egg mass data and the AP requirement was 1.7 g/kg and was computed at 95% of the asymptotic response. AP requirement for maximizing the egg production and egg mass was 2.8 g/kg of diet, when multiple responses (egg production and egg mass) were analyzed simultaneously by using the multivariate nonlinear mixed effects models. The results of this study revealed that the broken line models fitted the data better than other models. According to the broken line models, the range of optimal AP requirement of post molted laying hens for various responses were 1.8 to 2.5 g/kg of diet.