Empirical modelling the quality of pelleted feed for broilers and pigs

Abstract This study was developed to model the pellet quality to identify influential factors in an industrial pelleting process of feeds for broilers and pigs. Two independent databases were used to calibrate and to validate the models. Each column of the spreadsheet represented a descriptive variable of the manufacturing process (yield, amperage, pressure in the conditioner, and temperatures of the environment, the conditioner, and the cooler), feed characteristics (inclusion of the ingredients in the feed formula and bromatological composition of the main ingredients), and pellet quality (percentage of fines and pellet durability index - PDI). Each row of the spreadsheet represented one observation, or the equivalent of a lot of feed produced. The data were submitted to graphical analysis, descriptive statistics, and regression analysis by step-wise procedure. Three models were developed for each variable (yield, percentage of fines, and PDI): Model I, characteristics of the manufacturing process and inclusion of the ingredients in the formula; Model II, characteristics of the manufacturing process and weighted bromatological composition; and Model III, characteristics of the manufacturing process, inclusion of the ingredients in the formula, and weighted bromatological composition. The accuracy of the models (validation) was evaluated by the mean square of the predicted error (MSPE). The models obtained in this study differed from each other in the number of predictors selected in the statistical procedure. However, the main factors have been found repeatedly in the models. The amperage represented at least 22.84 % of the total variance, the cooling temperature responded by at least 2.93 %, and the inclusion of soybean oil in the feed formula accounted for at least 4.21 %. The models that considered characteristics of the manufacturing process and the inclusion of the ingredients in the formula (Models I) were the most accurate (lower MSPE) in relation to the Models II and III of each response. The pelletizing process requires constant monitoring in the feed factories and the models generated in this study are useful in the quality assurance sectors, providing a better definition of the monitoring parameters.